Q-switched regime of 3-um erbium lasers
Author(s):
Serban Georgescu;
Voicu Lupei;
Claudiu Hapenciuc
Show Abstract
A mathematical model, based exclusively on spectroscopic data concerning radiative, non-radiative, and energy transfer processes, is proposed and used to simulate the Q-switch regime of three-micron Er:YAG laser. The connection between the main energy transfer mechanisms that make possible generation on the self-saturated transition 4I11/2 yields 4I13/2 (up- conversion from 4I13/2 and 4I11/2, cross- relaxation from 4S3/2) and the giant pulse characteristics is discussed. The radiative as well as non- radiative losses during optical pumping and giant pulse generation are defined and evaluated. A particular attention is given to FTIR Q-switch which demonstrated real qualities for 3- micrometers Erbium lasers. The reasons responsible for experimental performances of Q-switched Er:YAG lasers inferior to those predicted by the mathematical modeling are analyzed.
Stabilization of unstable states in a modulated noisy CO2 laser
Author(s):
Valerica Ninulescu;
Paul E. Sterian;
Mihaela A. Ghelmez;
Mihai C. Piscureanu
Show Abstract
The work addresses the problem of a CO2 laser dynamics control in the presence of Gaussian white noise in the cavity losses. We improve the delayed continuous feedback method by introducing memory of the previous states. The method proves a powerful one that works for otherwise chaotic dynamics and regular dynamics equally well and it is robust with respect to noise.
Beam optimization of a TEA-CO2 laser
Author(s):
Tobias Gross;
Detlev Ristau;
Gordon Wallas;
Gabriel Dumitru;
Dan G. Sporea;
Clementina A. Timus
Show Abstract
The paper describes the methods used to adapt an industrial TEA- CO2 laser to the requirements of the ISO standard 11 254-2 for a laser induced damage threshold experimental facility. The goals were to improve the pulse energy stability and the laser beam spatial profile and the methods were: (1) finding the best discharge voltage; (2) adapting the laser cavity, (3) using suitable apertures. There is also presented the experimental set- up for beam characterization, which included a laser beam profiler (a line of 60 pyroelectric detectors), an energy-meter to monitor the pulse energies and KCl optical components for beam splitting and beam guiding. Every beam distribution was regarded as a linear combination of normalized Gauss-Hermite functions and the fitting algorithm allows the calculation of the coefficients of this combination.
Modeling optical amplification in Er3+-doped LiNbO3 waveguides
Author(s):
Niculae N. Puscas;
R. Girardi;
Danilo Scarano;
Ivo Montrosset
Show Abstract
Based on the small gain approximation in the unsaturated regime in this paper we present the derivation and the evaluation of the spectral optical gain, spectral noise figure and spectral quality factor on single and double pass configuration Er3+-doped LiNbO3 waveguide amplifier pumped near 1484 nm. The simulations show the evolution of the above mentioned parameters under various pumping regimes. In the present work we demonstrated that high gains and low noise figures are achievable in high pump regimes and double pass configuration. The obtained results can be used to theoretically model the optical amplification around 1500 nm in Er3+-doped LiNbO3 waveguides are function of various parameters.
Output beam characteristics of a Nd:YVO4 miniature laser
Author(s):
Nicolaie A. Pavel;
Takunori Taira;
M. Furuhata;
Takao Kobayashi
Show Abstract
The output beam characteristics of a CW diode end-pumped miniature Nd:YVO4 laser (1.1 at.%, 1 X 3 X 3 mm3) operating in fundamental and SHG regime are presented. Using M2 factor to describe the multimode pump beam's propagation from the broad-emission-area diode-laser the coupling optics was designed to obtain a high value for the mode-matching efficiency. A maximum slope efficiency of (eta) s equals 58.6%, with (eta) 0 equals 53.8% optically efficiency at maximum pump power, characterized a laser resonator of 50 mm length in transversal TEM00 mode. In the SHG experiments using a KTP crystal a maximum power of 100 mW was reach in a circular laser beam of 4.2 mrad half-angle divergence.
Bound-state excitation in ion-ion collision as related to the modeling of x-ray lasers with Li-like ions
Author(s):
V. Stancalie;
Alain Sureau;
V. M. Burke
Show Abstract
Within the framework of x-ray laser research using the recombination of heliumlike ions with free electrons to produce lithiumlike ions in expanding and cooling hot plasmas, we present a set of spectroscopic data required to improve the gain modeling. We estimate the cross section and rate for ion-impact excitation in aluminum Li-like lasing medium using the two-state approximation for transitions caused by a multipole interaction. The approximation used for atomic data calculation is presented.
Nd:YAG linear resonator using an external stimulated Brillouin scattering Q-switching mirror
Author(s):
Anca Mocofanescu;
Vasile D. Babin;
Sorin Miclos;
Ana-Florica Farcas
Show Abstract
We report Q-switching of a Nd:YAG laser with a phase-conjugating mirror based on external stimulated Brillouin scattering in carbon disulfide using a linear resonator. Q-switching is provided by a nonlinear LiF:F2- crystal before the stimulated Brillouin scattering takes place. Employing proper mode selectors pulses with 6 mJ minimum energy and duration of 20 ns were generated, the beam divergence being 1.5 the diffraction limit. A new theoretical model of the Q-switching regime has been proposed and good agreement between experimental and theoretical data has been obtained.
Excitation upconversion by sensitized photon avalanche
Author(s):
Voicu Lupei;
Eugen Osiac;
T. Sandrock;
Ernst Heumann;
Guenter Huber
Show Abstract
The features of a new upconversion mechanism of excitation, the sensitized photon avalanche, are discussed on the basis of a rate equation modeling. In this process the excited state absorption (ESA) from a metastable level (reservoir) of the active ion is enhanced by a cross-relaxation between the emitting level of this ion and the sensitizer ion which is able to transfer subsequently the accepted excitation back into the reservoir level of the activator; the donor act of the cross-relaxation ends on this reservoir level too. When the efficiencies of these two energy transfer processes are larger than specific threshold values related to the intrinsic de-excitation rates of the emitting level of activator and of the excited level of sensitizer, a process of population of the reservoir level with a quantum efficiency larger than the unit for each act of de-excitation of the emitting level takes place. Further on, if the ESA rate exceeds a threshold value determined by the intrinsic de- excitation of the reservoir and by the efficiencies of the energy transfers an avalanche population of these levels could take place. This process could be used for infrared pumping of visible solid state lasers. The theory is illustrated for Yb3+- sensitized visible emission of Pr3+ under infrared pump (835 nm).
Medium-power stabilized laser diode
Author(s):
Emil Smeu;
Niculae N. Puscas;
Ion M. Popescu;
Grigore I. Suruceanu;
Radu G. Ispasoiu
Show Abstract
Power stabilized DL's represent today convenient sources for radiometric applications, as transfer laboratory standards. Stability measurements were carried out and reported by other authors for different time intervals, but only for low optical power levels (max. 16 mW). For calibrating usual optical radiometers, such low emitted power DL's are useless. This paper reports stability measurements carried out on several collimated DL's with (lambda) around 980 nm and emitted power up to 265 mW in near-field/150 mW in far-field. Stabilities of the order 1e-4 for short-time intervals (tens of seconds) and 1e-3 for medium-time intervals (1 hour) were found for a non-thermostated structure, having the control photodiode (PD) in the same enclosure with the DL (at the rear of the structure). The corresponding stabilities for an external control PD resulted of the order 1e-5 for both short and medium time intervals. The schematic of the optical power stabilizer is presented.
High-resolution spectral analysis of a pulsed CuBr laser
Author(s):
Eugen Nicolae Scarlat;
Liliana Preda;
Constantin P. Cristescu;
Alexandru M. Preda
Show Abstract
A simple and inexpensive method to perform high resolution spectral studies of the green-yellow pulse shapes of a CuBr laser is presented. The radio-frequency (RF) spectrum of the temporal shape of the detected signal is called `pulse-shape spectrum (PSS). The individual 510.6 nm (green) and 578.2 nm (yellow) PSS are studied in the range 20 - 500 MHz with 1 MHz resolution. The RF spectral analyses of the compound signal (the weighted sum of the two pulses, one of them being delayed with respect to the other one) reveals that the coherence properties of the spectral components are dependent both on the pulsed mode excitation and the optical modes supported by the optical cavity.
Influence of active-medium properties on high-power solid state laser beam characteristics
Author(s):
Nicolaie A. Pavel;
Takunori Taira;
Traian Dascalu;
Voicu Lupei
Show Abstract
In order to describe the transversal mode construction in a real laser resonator, a mathematical model was investigated. The analysis use Kirchhoff-Fresnel diffraction equation and amplification processes in the active medium, that was supposed as sum of thin discs with gain and losses constants on every disc's length. Influence of additional phenomenon on laser beam characteristics, as phase-shift caused by active medium thermal induced refractive power and curvature of the resonator mirrors were considered.
Degradation effects in pulsed AlGaAs large optical cavity (LOC) structure laser diodes
Author(s):
Rodica V. Ghita;
Eugen Vasile;
Valerica Cimpoca;
N. Baltateanu
Show Abstract
High power pulsed laser diodes are of interest due to their potential use in medicine and peculiar applications. This paper presents failure analysis for catastrophic damage in GaAs/AlGaAs LOC pulsed laser devices. There is presented failure decrease of optical power as 1 g (P/P0) equals f(t) where P0 is initial power, P actual power, t-operating time. The damaged devices were investigated by optical and scanning electron microscopy and there was performed a electron dispersion spectroscopy analysis. These experiments advanced the idea of dividing catastrophic degradation in three types, respectively: 1-catastrophic optical mirror damage, 2-catastrophic damage due to major mechanic defects, 3-catastrophic damage due to metal migration (e.g. Au). There was established an experimental criterion to characterize catastrophic damage.
Performance of a pump system for diode-pumped lasers
Author(s):
Aurel Stratan;
Constantin G. Fenic;
Razvan V. Dabu;
Nicolae A. Herisanu;
C. Luculescu;
Dan G. Sporea;
Gabriel Dumitru;
Gheorghe Iordache
Show Abstract
We have developed a laser-diode pump system for continuous-wave end-pumping of Nd:YAG lasers. The pump system includes a pair of 1 W diode-arrays mounted in coaxial enclosures, a driver unit and the pump optics. The array wavelength was temperature tuned to achieve the maximum absorption of the pump radiation in the Nd:YAG crystal. The characteristics of the pump system are presented and the pump-beam profile is investigated.
Medium-power cw He-Se laser
Author(s):
Marin Ristici;
Iosefina Ristici;
Victor Rares Medianu
Show Abstract
We have developed a simple, all Pyrex, 60 cm active length laser tube in a self-heating geometry. For a He pressure of 20 Torr and a current of 120 mA, the laser power was 28 mW on seven lines in the blue-green region. By spectroscopic measurements we have determined the influence of metal vapor presence on the intensity of a helium line. Some modifications of the vapor clouds generated by a magnetic field are reported.
Pump distribution effects on photon avalanche in fiber lasers
Author(s):
Voicu Lupei;
Eugen Osiac
Show Abstract
The paper discusses the effect of pump intensity variations caused by absorption in a fiber system with upconversion avalanche fluorescence or laser emission. The numerical modeling shows that in given pump conditions the initial part of the fiber (up to a distance zth) is pumped above the avalanche threshold while the remaining part lies below it. This induces a strong variation of populations of the excited levels along the fiber. The characteristics of the avalanche emission are connected to the spectroscopic parameters of the system and to the conditions of pump. It is also shown that the features of the global luminescence emission at the end of fiber depend strongly on the fiber length for the short fibers (L <EQ zth) but for the long ones this dependence diminishes; thus the avalanche emission of a long fiber could be different from that predicted by a constant rate modeling. The effect of distribution of local pump intensities on laser emission in avalanche-driven upconversion fiber lasers is also discussed.
High-quality beam transversal gas transport cw CO2 laser
Author(s):
Iulian Gutu;
Victor Rares Medianu;
Petre Cristian
Show Abstract
A new optical resonator configuration for transverse flow CO2 laser was developed. A high value of the matching coefficient (the cross section of the laser beam/the cross section of the electrical discharge)-(eta) m, is obtained for laser beams with TEM00/01 intensity distribution (that corresponds to the low values of the Fresnel number-NF of the optical resonator). Simultaneously, both types of the gain and refractive index asymmetries of the active medium (parallel and perpendicular on the flow direction) are compensated. A 90 degree(s) deflection device is the main constructive element (this is built by two mirrors at 45 degree(s) relative angle and offers the pentaprism properties). This deflection device reverses the wavefront in one of the two discharge channel and in addition improved the resonator stability. The main results are (eta) m is congruent to 0.83 for NF is congruent to 1.9 and the beam pattern is independent of the power level in the range of 300 W to 1800 W.
Comparison between method of lines and time domain method in evaluating the large signal responses of Fabry-Perot semiconductor lasers
Author(s):
Ada Livia Braverman
Show Abstract
An extensive comparison between two modeling methods: Method of Lines and Time Domain Method in analyzing the large signal responses of Fabry-Perot semiconductor lasers is presented. The methods are implemented in two numerical codes written in FORTRAN and using DIGITAL ALPHA workstations under VAX/VMS and UNIX operating systems. The comparison shows good agreement between the simulation results under specific conditions. A special accent is placed on the advantages and drawbacks of both methods by taking into account their numerical problems and the computational effort implied by simulations.
Generalized model for cw three-micron emission in concentrated Er systems
Author(s):
Voicu Lupei;
Serban Georgescu
Show Abstract
A generalized model of the cw three-micron emission in concentrated Er systems, which takes into account the whole variety of de-excitation processes is presented. The analytical equation for the flux of light enables a direct correlation of the parameters of emission (threshold, slope efficiency) with the spectroscopic parameters and pump conditions. The effect of excited state absorption is, also, put in evidence.
Synthesis, characterization, and mechanical properties of carbides and nitrides films prepared by pulsed-laser-deposition method
Author(s):
Ashock Kumar;
H. L. Chan;
Rodica Alexandrescu
Show Abstract
Carbides and nitrides of metal have a large number of applications in modern technology owing to their interesting, and in some ways unique, physical and chemical properties. Thin film coatings of titanium carbide and aluminum nitride were deposited on Si (100) substrates using pulsed laser deposition method. The structural and microstructural properties of these films have been characterized using x-ray diffraction, and Fourier transform infrared spectroscopic techniques. The mechanical properties of the films were evaluated to measure the hardness and modulus values. It has been shown that the films deposited at higher temperature have the best crystalline quality structure and also have higher hardness values compared to the film deposited at lower temperatures.
Deposition of CN thin films by reactive pulsed laser ablation
Author(s):
Alessio Perrone
Show Abstract
The effects of laser fluence on the structure and properties of the reactive pulsed laser deposited carbon nitride (CNx) thin films prepared at different gas pressures of N2 and NH3 were investigated. The structure, the morphology and the chemical composition of the films were characterized by X-ray photoelectron spectroscopy, X-ray diffraction, transmission electron microscopy, scanning electron microscopy, Rutherford backscattering and Fourier transform infrared. The films were plane, adhesive and relatively hard, with a low droplet density. The deposition rate decreases with increasing gas pressure and laser fluence, while the N/C atomic ratio increases. The nitrogen concentration in the deposited films drops when the substrate temperature is increased, indicating a desorption process of the CN radicals. Spectroscopic studies of the plasma plume indicates an interesting correlation between the CN band emission intensity and the nitrogen concentration in the samples.
Laser diagnostics in flame deposition of diamond
Author(s):
R. J. H. Klein-Douwel;
J. J. ter Meulen
Show Abstract
Combustion diagnostics by means of 2D Laser Induced Fluorescence (2D-LIF) is applied to a diamond depositing oxyacetylene flame. The method and results of diamond growth are discussed, as well as the 2D-LIF technique. The distributions of atomic hydrogen, CN, and C2 in the flame are presented together with their relations to diamond growth.
Synthesis of nanosize powders by pulsed laser ablation and related plasma diagnostics
Author(s):
Kiyoshi Yatsui;
Weihua Jiang;
K. Nishiura;
T. Yukawa;
Constantin Grigoriu;
Ioan Chis;
Aurelian Marcu;
Dana Miu
Show Abstract
Nanosize powders of AlN was successfully synthesized by pulsed laser ablation. The target can be either Al or AlN, with ambient gas nitrogen. With Al targets, typical powder diameters were in the range of 2.5 divided by 25 nm. In order to study the process of powder formation, we have used a high-speed camera and a time-resolved spectrum analyzing system to investigate the behavior of the ablation plasma and the ion species in the plasma. For the diagnostic experiments, the target was Al and the ambient gas was oxygen.
X-ray micromachining with a laser-plasma source at 1-nm wavelength
Author(s):
I. C. Edmond Turcu;
Chris M. Mann;
Sung W. Moon;
B. J. Maddison;
Ric M. Allott;
Nicola Lisi;
Syed Ejazu Huq;
Nam Seong Kim
Show Abstract
A picosecond excimer laser-plasma source has been constructed which generates an x-ray average power of 2.2 Watt and 1.4 Watt at the wavelengths required for proximity x-ray lithography: 1.4 nm (steel target) and 1 nm (copper target), respectively. The plasma source could be scaled to the 50 - 75 W x-ray average power required for industrial lithographic production by scaling the total average power of the commercial excimer laser system up to 1 kW. The 1 nm x-ray source is used to micromachine a 2.5 THz microwave waveguide-cavity package with a 48 micrometers deep, 3D structure, using the LIGA technique.
Preparation of metal oxides by laser versus thermal processes
Author(s):
Rodica Alexandrescu;
Ion G. Morjan;
C. R. Popescu;
Ion N. Voicu
Show Abstract
The study of producing metal based oxides has become increasingly interesting because of several specific features which make them extremely attractive for various uses, e.g.: catalysts, pigments, magnetic records, sensors, etc. In the present paper we report the synthesis of various iron, copper and nickel oxides by the IR laser processing of different salts. X ray diffraction technique was used in order to characterize the reaction problems. An analysis of the differences between these oxides and those obtained from the same salt by thermal means is presented. It was found that the oxides obtained by laser processing show specific characters concerning the crystallinity and chemical composition.
New studies of reactive pulsed laser deposition
Author(s):
Ion N. Mihailescu;
Eniko Gyorgy;
Valentin S. Teodorescu;
Gheorghe Marin;
D. Pantelica;
A. Andrei;
Johny Neamtu
Show Abstract
We report the synthesis and deposition of TiC films by reactive pulsed laser deposition. Ti targets have been submitted to multipulse UV laser action in low pressure CH4. The thin films were grown on a collector placed parallel to the target. The films were characterized by electron microscopy, electron spectroscopy and nuclear techniques.
Discharge-aided reactive laser ablation for ultrafine powder production
Author(s):
Ioan Chis;
Aurelian Marcu;
T. Yukawa;
Dumitru Dragulinescu;
Constantin Grigoriu;
Dana Miu;
Weihua Jiang;
Kiyoshi Yatsui
Show Abstract
Ultrafine alumina powder was produced by aluminum target ablation with a Nd:YAG laser beam (1064 nm wavelength; 340 mJ/pulse energy; 7 ns pulse duration; 10 pps repetition rate), in a 120 Torr O2 atmosphere. A theoretical approach for the ablation process, based on laser energy absorption and energy balance in the target, is used for comparison with the experimental production rate. Three experimental irradiation conditions were chosen: (1) energy density of 5 J/cm2, considered reference (RDE), (2) lower energy density of 2.5 J/cm2 (LDE) and (3) RDE with auxiliary discharge between an auxiliary electrode and target, triggered by the ablation plume (RDA). Calculated and experimental data of target weight loss show good agreement (135 ng/pulse, calculated, and 100, 110, 120 ng/pulse, experimentally, for RDE, LDE, RDA conditions, respectively). The X-Ray Diffraction spectra of alumina show formation of (gamma) -alumina particles only, especially in LDE and RDA conditions. From Scanning Electron Microscopy size analysis, a decrease of particle size, in LDE and RDA irradiating conditions, is observed. The decrease of laser beam fluence or aiding of ablation using an auxiliary discharge is both favorable for the production of high quality powder, without diminishing the production rate. This can be a good basis for future improvement of the ultrafine powder production process.
Deposition of carbon nitride thin films by IR-laser-induced reactions in carbon-nitrogen gas-phase compounds
Author(s):
Aurelian Crunteanu;
Rodica Alexandrescu;
Raluca Cireasa;
S. Cojocaru;
Ion G. Morjan;
A. Andrei;
Ashock Kumar
Show Abstract
Since the theoretical studies of Liu and Cohen who predicted the existence of a superhard phase of carbon nitride, a great deal of effort was underdone in order to synthesize this hypothetical material with a nitrogen content as high as the 57% present in a (beta) -C3N4 structure. This study presents an attempt to produce CNx thin films using the laser-induced CVD technique. CW CO2 laser was used for irradiating various carbon-nitrogen containing mixtures such as C2H4/N2O/NH3. The CNx films were grown alternatively on bare alumina ((alpha) - Al2O3) substrates and on pre-deposited Ti films. A comparative analysis of nitrogen incorporation in the films obtained in different experimental conditions was performed by means of the X-ray photoelectron spectroscopy. The same method was used to identify the chemical states of the CN system.
Influence of thermal annealing on optical properties of porous silicon films
Author(s):
I. Baltog;
M. L. Ciurea;
Gabriela Pavelescu;
E. Pentia;
G. Galeata;
Jean Paul Roger
Show Abstract
The influence of the thermal annealing on the optical properties of the porous silicon films was revealed by photoluminescence (PL) and spectroellipsometric measurements. As result of 200 degree(s)C annealing small changes of the dielectric functions could be understood by desorption process of some molecules from Si skeleton surface. Strong changes of PL and dielectric function spectra after the thermal annealing at high temperatures (up to 800 degree(s)C) were explained by the change of the passivation from hydrogen to oxygen and then the beginning of the oxidation process. This oxidation process produces the disappearance of the PL slow component, an important enhancement of PL (2-3 orders of magnitude) and a shift of maximum position to higher energies, corresponding to the thinning of the nanocrystallites from the Si skeleton.
Optical devices with silica-gel small spheres
Author(s):
Alexandru M. Preda;
Eugen Nicolae Scarlat;
Liliana Preda;
Ion M. Popescu
Show Abstract
Some inexpensive optical devices using small silica-gel spheres are presented. The silica-gel spheres of good quality are investigated under the microscope. These sphere presents some particularities which make them very useful in applications like interferometry, hygrometry and optical microscopy. Such small spheres may be doped with microcrystals or dye solution in order to study a large range of nonlinear phenomena. Experimental studies have been performed on the silica spheres as alternative media for laser action using a pulsed CuBr laser as excitation source.
Growth of polycrystalline hydroxyapatite thin films by pulsed laser deposition and subsequent heat treatment in air
Author(s):
V. D. Nelea;
Cornel Ghica;
C. Martin;
Alexandru Hening;
Ion N. Mihailescu;
Leona C. Nistor;
Valentin S. Teodorescu;
Rodica Alexandrescu;
J. Werckmann;
Eniko Gyorgy;
Gheorghe Marin
Show Abstract
Hydroxyapatite (HA), Ca10(PO4)6(OH)2, is the primary constituent of the human bone and one of the best biocompatible materials. In this work we developed a simple method for the deposition of polycrystalline HA thin films onto various collectors including substrates of medical interest (e.g. Ti). We proceeded by the pulsed laser deposition of HA targets onto parallel collectors placed at (2-5) cm in vacuum. After deposition the films were heated in air at 500 degree(s)C for 30 minutes. The heated film has a structure which appears in electron diffraction as identical to the structure of the base material. The obtained films are uniform and very adherent to the substrate. The P/Ca atomic ratio, determined by energy dispersive X-ray analysis, was found to be close to that characteristic to HA, for the post-depositing heated films.
Mechanisms of droplet formation in pulsed laser growth of thin oxide films
Author(s):
Valentin Craciun;
Doina Craciun;
M. C. Bunescu;
Eugen Vasile;
A. Ioncea;
Razvan V. Dabu;
Ian W. Boyd
Show Abstract
The role of the sub-surface explosive boiling mechanism for droplet formation during the pulsed laser deposition of thin films has been examined. For photons with an energy lower than the target optical band-gap, hv<Eg, a highly perturbed target surface morphology exhibiting micrometer sized round- shaped cavities always formed, whereas for hv>Eg the surface was much less perturbed. Depth-profile estimations of the temperature profiles inside the laser irradiated targets were also quite different for these two cases. For low optical absorption coefficient (OAC) values, (alpha) < 5 X 104 cm-1, a thick layer of liquid formed whose maximum temperature was located at some point below the surface. Simultaneous to the cavity formation, the droplet density on the surface of the grown films was found to increase by orders of magnitude, indicating a clear connection between the target OAC, the temperature profile, the presence of the cavities and a high droplet density. The decrease of the OAC value during prolonged laser ablation could also explain the gradual increase of the droplet density observed when growing La0.5Sr0.5CoO3 films. Based on these results, we suggest that an important fraction of the droplets on the surface of films grown under laser irradiation conditions where the OAC is smaller than 5 X 104 cm-1 is caused by an explosive sub-surface boiling mechanism.
Nd:YAG laser surface texturing
Author(s):
Marian Poterasu;
Traian Dascalu;
A. Marian;
Dan Mihhi Buca
Show Abstract
Obtaining sharp and sometimes special patterns on hard materials surfaces (texturing) is rather difficult by conventional procedures, which made the laser an attractive choice in this matter. Absorption of Nd:YAG's 1.06 micrometers radiation in most steels and ceramics, which are the common materials for textured surfaces, is good such that average power lasers can be used. In this paper we are concerned with the principal phenomena involved in the texturing process and with the sought of a simple mathematical model that will allow to choose right working regime, and make estimations about the system performances (speed, power consumption, etc.). Experimental data were obtained by using both a Electro-Optically Q-switched CW laser with an average power of up to 100 W and a pulsed free running laser with an average power of up to 100 W and pulse energy of up to 10 J. The experimental set-up includes an X-Y stage and two gold deflectors used to cover the entire surface.
Investigation of HgBrxI2-x using confocal laser scanning microscopy and x-ray diffraction
Author(s):
George A. Stanciu;
J. L. Oud;
E. K. Polychronyadis;
Maria Daviti;
Angelia Stanciu;
Catalin Miu
Show Abstract
The compound Mercuric Bromoiodide (HgBrxI2-x) belongs to the HgI2-HgBr2 system. It is promising for the same applications as HgI2, that is as solid state X and (gamma) detector, operating at room temperature since it exhibits a number of properties which are necessary for such applications, i.e. large atomic number, large band gap (2.4 - 3.4 eV) and high resistivity. Using a Confocal Laser Scanning Microscope we made some investigations regarding topographical distribution of impurities or related defects. Analysis of chemical composition of HgBrxI2-x crystals were performed on a SEM model Phillips 515 equipped with Energy Dispersive X-ray Analysis.
Lasers for material processing
Author(s):
Alexandru Nichici;
Ion David;
Eugen F. Cicala
Show Abstract
The selection of the best laser for a given application is a common problem of laser users. However, a direct relationship between laser intrinsic characteristics and a potential application, risks to make the laser source selection process unilateral and partially mistaken. In fact, the best processing technology for a given application must be chosen. Therefore, the present paper proposes an indirect, more realistic selection process. This process starts from a general laser application definition. Then, it passes through the analysis of the needed laser beam--workpiece material interaction and of the necessary laser technological system. Finally, the selection process ends with the laser processing technology definition, where the choice of the most suitable laser source becomes in fact possible.
Effects of UV laser radiation on the surface defects of NiO catalysts
Author(s):
Eugenia Ivana;
Veronica Lacatusu;
Mariana Chelu;
Mariana Craiu;
Constantin G. Fenic;
Aurel Stratan;
Leona C. Nistor;
Cornel Ghica;
P. Marginean
Show Abstract
NiO is a metal-deficient p-type semiconductor with surface defects which are correlated with the non-stoichiometry. The dissociative H2 adsorption on the NiO surface takes place on oxygen-excess sites (over equilibrium). The H2 TPD spectra vary significantly with calcination temperature (stoichiometry) and chemical treatment UV laser radiation enhances H2 adsorption on the defective surfaces (non-stoichiometric) as compared with the stoichiometric ones, even chemically treated. The fourth harmonic of a Q-switched Nd:YAG laser is used for the NiO samples irradiation. The wavelength of the UV laser radiation is 266 nm, under the band-gap of the semiconductor.
Modeling of chalcogenide glass structures before and after laser illumination, based on mass spectroscopy data
Author(s):
Andrei M. Andriesh;
Arthur I. Buzdugan;
Valentin Dolghier;
Mihai S. Iovu
Show Abstract
In this communication we present the results of computational modeling of molecular units as AsmSn registered by mass spectrometry in the As2S3:Snx glasses before and after laser illumination. Using HyperChem Computational Chemistry program we obtained 3D structures, with global minimum energy conformation for following molecules: As4 (3.47); S8 (4.44); As4S3 (11.87); As2S5 (14.36); As2S4 (17.62); As2S6 (19.11); As4S4 (21.88); As4S5 (24.98); As2S3 (25.81); As4S6 (43.13). The model of the As2S3:Sn0.1 glasses, using 200 As atoms, 300 S atoms and 10 Sn atoms for computational modeling, is presented too. Such model shows that a tin atom may be bonded in two ways: when the tin atoms are common for two rings with 12 atoms and when the tin atom are bonded between the layer of the glassy network. When the tin atom are insert in the network rings for 12 atoms the structural model shows the more compact packing of the atoms.
Ionic space-charge-limited currents in natural quartz crystal
Author(s):
Ionut Enculescu;
Brandusa Iliescu
Show Abstract
Arrhenius plots and current-voltage characteristics were studied for natural quartz samples, in different conditions of air- sweeping time, of temperature, of electrodes (with or without any source of positive ions). Some observations about the influence of the ionic space charge limited current are made. Some dependencies of ionic current versus voltage were found.
Compacting of metallic powder by using Nd:YAG laser
Author(s):
A. Marian;
Dan Mihhi Buca;
Traian Dascalu;
Marian Poterasu
Show Abstract
The processes involved in the melting and solidification of powders have been studied, in order to obtain 3D pieces. The experiments have been performed with a CW Nd:YAG laser, but the Q-switched regime has been also used. Measurements about compacting rate for different parameters (scanning speed, thickness of layer) and a comparison between the two regimes have been made.
Microstructure of hydroxyapatite thin layers grown by pulsed laser deposition
Author(s):
Doina Craciun;
Valentin Craciun;
C. Martin;
Ion N. Mihailescu;
M. C. Bunescu;
Eugen Vasile;
A. Ioncea;
Ian W. Boyd
Show Abstract
Thin films of hydroxyapatite (HAp) have been grown on Si, quartz, Ti, and Ge substrates by the pulsed laser deposition (PLD) method employing a KrF excimer laser (wavelength (lambda) equals 248 nm, pulsed duration (tau) FWHM equals 20 ns). The influence of the laser deposition parameters on the properties of the grown layers was investigated in order to optimize the Ca/P ratio and the crystalline structure. It was found that the optimum conditions for preserving the Ca/P ratio i.e. high oxygen pressures and low substrate temperatures do not coincide with those for obtaining adherent and crystalline layers i.e. low oxygen pressures and high substrate temperatures. For films deposited onto Ti substrates it was also found that high substrate temperatures promote the diffusion of Ti through the depositing film up to the surface where it gets oxidized. Further investigations are required before high quality HAp-coated Ti implants by PLD can be obtained.
Computing coupling coefficients in transmission systems
Author(s):
Violeta Calian;
Marcela Ursache;
Cristian Sarpe-Tudoran;
Margareta Socaciu
Show Abstract
A numerical method for simulating realistic problems of mode coupling in optical transmission systems is described. The conclusion concerning waveguided propagation of the electromagnetic field in complex structures, selective mode excitation and the power transfer may become an important factor in designing and connecting devices used in optical signal processing. The numerical method is based on an extension of the `Orthogonal Collocation Method' to the case of coupled systems of differential equations with an infinite range of independent variables.
Effect of pulsed-laser deposition parameters on plasma expansion studied by fast-framing photography
Author(s):
Dana Miu;
Aurelian Marcu;
T. Yukawa;
Constantin Grigoriu;
Ioan Chis;
Kiyoshi Yatsui
Show Abstract
Fast-framing photography was used to study the effect of various parameters on the expansion of the visible plasma plume produced by KrF laser irradiation of a YBa2Cu3O7-x target. The ambient gas pressure has a considerable effect on the evolution and structure of the plasma. In vacuum, the visible emission is strongly forward-directed and has a relatively short duration. In the presence of an oxygen atmosphere, a long-lived, highly luminous front is formed, whose expansion may be well described by a drag model or a shock model (spherical or plane shock). Ahead of the luminous front there is weak emission, which for pressures over about 700 mTorr evolves into a highly emissive `tip'. The decrease of energy density on the target by increase of the laser spot (defocusing) leads to a more forward-directed motion of the visible species. Larger energy densities obtained by increasing the energy/pulse lead to a sharper, `V' shaped front. The effect of a biased ring electrode placed 0.5 cm to 2 cm in front of the target was also studied. The emission characteristics in the electrode's presence change greatly. The effect of ring-target distance, voltage magnitude and polarity, and pressure were observed.
Synthesis of europium-activated calcium tungstate phosphor
Author(s):
Elisabeth-Jeanne Popovici;
Flavia Forgaciu;
Miloslava Nemes;
Veronica Ursu
Show Abstract
The purpose of this study is to establish the way in which different synthesis conditions influence on the structural and luminescent characteristics of europium activated calcium tungstate powder phosphor. CaWO4:Eu3+ samples were prepared by thermal synthesis from mixtures consisting of precipitated-CaWO4, equivalent amounts of Eu2O3 and WO3 (activating system) and CaCl2 or Na2WO4 as flux. Calcination was performed at 800 - 1000 degree(s)C for 2 h, in air. The crystalline structure (XRD-patterns) and luminescent characteristics (emission and excitation spectra of phosphor samples were determined and interpreted.
Off-line multiresponse optimization of gas-jet-assisted CO2 laser cutting of polymettacrylate
Author(s):
Eugen F. Cicala;
Delia Zsivanov;
Alexandru Nichici
Show Abstract
From the phenomenological point of view, laser cutting processes are complex, weakly organized and diffuse systems. Off line optimization of such processes demands relative simple, but accurate enough models, which could be obtained by experimental way. The article presents the results of a large factorial designed experiment, having three main objectives: to identify which factors are statistically important, to build a quantitative model relating the important factors to the response functions, to optimize these response functions and particularly the material removal rate, the kerf walls parallelism deviation and the specific energy consumption. The obtained results allow the choice of laser cutting optimal parameters.
Establishing the regression polynomials for the objective function that defines dimensional accuracy in the case of laser drilling
Author(s):
Ion David;
Eugen F. Cicala
Show Abstract
The aim of the paper is to optimize the microholes machining, in the case of laser drilling. The laser used for experiments was a Neodim-15 laser. The material used for drilling was 41MoCr11 austenitic stainless steel with a 1,5 mm thickness. As parameters of the laser drilling process were considered: diaphragm diameter, focal point position, focal length of the lens and laser pulse power. The objective functions were the diameter of the microhole in the area of the laser beam entrance of material (Di), the diameter of the microhole in the area where the laser beam exit the material (De), respective their tolerances (Ti and Te). It was used on complete factorial experiment 24. The established mathematical models are useful in finding the optimum values of the parameters in various combinations, such as the hole diameter to be closer to the required diameter.
Theoretical model for the reactive pulsed deposition process: application to the case of ablation of a Ti target in low-pressure N2
Author(s):
Johny Neamtu;
Ion N. Mihailescu
Show Abstract
We introduce a theoretical model to describe all the phenomena implied in the interaction process between the high intensity UV laser radiation and a solid target in the ambience of a low- pressure chemically active gas. The action of the laser radiation upon the solid surface is simulated by solving the 1D heat equation. A hydrodynamical 1D model was further applied to describe the interaction between the laser radiation and the plasma expanding in front of the target. The absorption of the laser radiation in the vapor plasma could be considered with the aid of a multifluid model. The transit of the ablated atoms and/or of the new formed chemical compound was approached with a Monte-Carlo method. We could compute time and space distribution of the main plasma parameters (e.g. the plasma density and temperature). We could finally predict the thickness distribution of a film deposited on a collector placed parallel to the target at a distance of (1.5 - 3) cm range. The calculus was conducted for the case of a Ti target in low pressure nitrogen.
Pulsed-laser and alpha particle irradiation effects in Fe-based glassy ferromagnets
Author(s):
M. I. Toacsan;
D. Barb;
M. Sorescu;
B. Constantinescu;
L. Jeloaica
Show Abstract
A comparatively study of pulsed-laser and alpha particle irradiation effects in metallic glasses has been performed in order to understand the relationship between magnetic behavior and select variations in the structural characteristics of alloy phases. Samples of Fe78B13Si9 and Fe66Co18B15Si metallic glasses were irradiated with a pulsed excimer laser ((lambda) equals 308 nm, (tau) equals 10 ns) and alpha particle beams (W equals 2.8 MeV) using radiation doses of 1016 and 1017 cm-2. Irradiation-driven changes in the magnetic anisotropy and phase equilibrium of alloy samples were studied by Mossbauer Spectroscopy and scanning electron microscopy. The evolution of phases and microstructure during the radiation- induced amorphous-to-crystalline transformations or revitrification depend on the specific irradiation and sample composition.
Quantum optics of a single atom
Author(s):
Herbert Walther
Show Abstract
In this paper recent experiments performed in our laboratory are reviewed dealing with the investigation of quantum phenomena in the radiation interaction of single atoms. The first part describes experiments in single mode cavities using the one-atom maser or micromaser and in the second part experiments with ion traps are summarized. The latter experiments concentrate on the investigation of resonance fluorescence. In addition new experimental proposals using ultracold atoms in cavities and traps are discussed. In those future experiments the interplay between atomic waves and light waves is important and leads to new phenomena in radiation-atom interaction.
Novel femtosecond optical solitons in weakly excited semiconductors
Author(s):
Dumitru Mihalache;
Igor V. Mel'nikov;
Nicolae-Coriolan Panoiu
Show Abstract
We apply the quasiadiabatic approximation for the femtosecond pulse propagation in a collection of excitons in the case of weak interaction between the optical pulse and the semiconductor medium. Using the semiconductor Maxwell-Bloch equations beyond the slowly varying envelope approximation we show that the dynamics of femtosecond pulse propagation is described by the modified Korteweg-de Vries equation. Bright solitons superimposed on a continuous wave background are found and their stability against low amplitude perturbations is investigated. Possible experiments in semiconductor systems such as GaAs/AlGaAs are discussed.
Various approaches for optical implementation of the wavelet transform
Author(s):
Emanuel Marom;
David Mendlovic;
Zeev Zalevsky
Show Abstract
The wavelet transform is a very common and useful tool for image processing and compression, however, it requires heavy computations. Optics is useful for rapid computation of parallel information channels. In this paper various important approaches for the optical implementation of 2D wavelet transform as well as the optical wavelet processor are presented and discussed.
Radiation spectrum and the thermodynamics of quantum cubic cavities
Author(s):
Valentin I. Vlad;
Nicholas Ionescu-Pallas
Show Abstract
In this paper, the density of modes in quantum cubic cavities is calculated taking into account the small number of modes. Then the `spatial quantization' fluctuations, which appear as a correction factor in the mode density, are introduced in the Planck law. The discrete form of the Planck radiation spectrum is demonstrated and the limits of this double-quantum regime of the cubic cavity are set for the product of cavity size by temperature. LT(epsilon) (0.1, 1). A reciprocity rule for the cavity size and the temperature is shown. Calculating the total energy in the quantum cubic cavities (QCC), we found out a `corrected' Stefan-Boltzmann law for the double-quantum regime. Furthermore, the corrections for all thermodynamic functions of the photon gas in QCC are given.
Photoinduced phenomena in chalcogenide glasses and their application in optoelectronics
Author(s):
Andrei M. Andriesh
Show Abstract
The interaction of radiation with vitreous materials provokes irreversible and reversible changes of atomic and electronic structures. These changes in their turn manifest themselves in the experiment through changes of mechanical, thermal, optical, photoelectrical and other characteristics. Under the radiation influence the structure of vitreous materials changes, new defects appears, film crystallization or amorphization takes place, phase transition or transition from one unstable state to another. It is evident that such changes radically influence the optical and photoelectrical properties of the material: the refraction index and other optical material constants change; reflection and absorption of light as well as photoelectric parameters. Of no less importance is the appearance of new possibilities for application of vitreous materials as optical and photoelectrical recording media, fibers and planar waveguides, active and passive elements of optoelectronics, including nonlinear elements and sensors of different physical quantities. This paper covers a survey of works dedicated to the research of various photoinduced phenomena in bulk, thin-film and fiber samples of chalcogenide glassy semiconductors.
Thermo-optic dispersion formula of AgGaSe2 and its applications to thermal lensing effects
Author(s):
Eiko Tanaka;
Kiyoshi Kato
Show Abstract
The thermooptic constants of AgGaSe2 have been measured at 2.052, 3.3913, 5.2955, and 10.5910 micrometers . These results combined with the literature values were used to construct the thermooptic dispersion formula which correctly reproduces the temperature dependent phase-matching conditions for second-harmonic generation and sum-frequency generation of a CO2 laser as well as the thermally induced lensing effects for the 2.05 micrometers pumped parametric oscillators.
Possibility of two-photon superradiance in microcavities
Author(s):
Mihai Macovei;
Nicolae A. Enaki
Show Abstract
We analyze the two-photon cooperative emission of excited atoms in microcavities with dimensions of the order of the emission wavelength. Here the two-photon dipole-forbidden transitions between the upper and the ground states of the three-level system are possible through the intermediate level that is off resonance with microcavity modes. In this situation one obtains the powerful pulse of two-photon highly correlated light. The superbunching phenomenon in radiated field is also discussed.
Nonlinear excitonic susceptibilities of semiconductors at high levels of excitation
Author(s):
P. I. Khadzhi;
D. V. Tkachenko
Show Abstract
The hysteretical behavior of imaginary and real parts of the semiconductor susceptibility in the exciton range of spectrum taking into account the exciton-photon and elastic exciton- exciton interaction in the pump-probe regime depending on the intensity and frequency of the strong pump laser pulse and on the frequency of the test pulse is studied. The conditions of the emergence of the damping suppression and test pulse gain are determined. The abrupt red and blue shifts of the spectral position of the exciton absorption band depending on the intensity of the pump pulse are predicted.
Appearance and suppression of stochastic self-pulsations of coherent excitons and biexcitons in condensed matter
Author(s):
V. Z. Tronciu;
A. H. Rotaru
Show Abstract
The theory of regular and chaotic self-pulsations in a CuCl crystal with the participation of coherent excitons and biexcitons is elaborated. The method of chaotic self-pulsation suppression in the system of coherent excitons and biexcitons is proposed. This method consists in action of external periodical turbulence upon a stochastic system. The range of amplitude values and frequencies of external harmonic pump were found at which the chaotic oscillation regime becomes nonlinear periodic by transformation of strange attractor into a limit cycle. The feasibility of observing the predicted effects in experiment is discussed.
Novel approaches in morphological correlations
Author(s):
David Mendlovic;
Amir Shemer;
Zeev Zalevsky;
Emanuel Marom;
Gal Shabtay
Show Abstract
Morphological correlation is a novel method for obtaining high discrimination ability in pattern recognition applications. It provides also important abilities for image compression and image analysis. The concept is based on slicing the input image and the reference filter into many binary slices, e.g. 255, and correlating them. The morphological correlation is defined as the summation of these correlations. The morphological correlation is characterized by a sharp correlation peak narrower than that exhibited by matched filter. The disadvantages are the requirements of performing many correlations and its very high sensitivity to noise added to the reference image. In this presentation we suggest two methods to solve both drawbacks. First, instead of 255 correlations we suggest to utilize only 8, by representing the grey level of each pixel by its 8 bit binary representation. Then, 8 binary masks are constructed according to the binary representation. In order to address the problem of severe sensitivity to noise, we suggest to sum the 255 correlations of the morphology slices while each slice is multiplied by a weighting factor which equals the correlation peak of that specific slice with noise divided by its correlation peak value when no noise is added. The solutions suggested here were examined by computer simulations demonstrating considerable improvements in the performance of the morphological correlator.
Rotation-invariant pattern recognition using circular harmonics and synthetic discriminant functions
Author(s):
Dan Cojoc
Show Abstract
The use of circular harmonics to design correlation filters represents one of the most powerful approach in one-target recognition with in-plane rotation invariance. Recognition of more than one target can be achieved, on the other hand, using synthetic discriminant functions. In this paper we describe how can be combined these two techniques to design a filter which ensures rotation invariant recognition of multiple targets in parallel. The usefulness of the filter is demonstrated, for the case of two targets, by experimental results obtained from computer simulations.
Surface study of laser-induced charge gratings in Bi12SiO20 with an atomic force microscope
Author(s):
E. Soergel;
W. Krieger;
Valentin I. Vlad
Show Abstract
Light-induced charge gratings at the surface of a photorefractive Bi12SiO20 crystal are investigated using electrostatic force detection with an atomic force microscope. The gratings with periods of 2.7 micrometers and 0.22 micrometers are generated by two intersecting Ar+-laser beams at 514 nm. The dark decay times of the stored gratings are determined. Saturation processes are directly observed by a change of the profile of the charge gratings. The polarity of the charge carriers in the material is obtained using a simultaneous measurement of the light-intensity grating.
Optical bistability in short-external-cavity DBR semiconductor lasers
Author(s):
Victor B. Guja;
Ivo Montrosset;
Ovidiu D. Iancu
Show Abstract
The bistability that we are describing results from designing properly the cavity of a Distributed Bragg Reflector laser realized with an external fiber grating and is based on longitudinal mode competition. The analysis of the output power bistability is done with a simulation of the static behavior of the laser. An accurate and fast computing algorithm has been implemented to solve the steady state rate equations for photon and carrier density. The used model is based on multimode analysis and includes gain saturation.
Nonlinear optical properties of noncrystalline semiconductors
Author(s):
Valentin N. Ciumash
Show Abstract
The paper summarizes the peculiarities of the nonlinear interaction of short laser pulses with the noncrystalline semiconductors (chalcogenide glasses, a-Si:H), showing that noncrystalline semiconductors (NS) are an interesting material for high speed optoelectronics. The physical mechanisms, which can contribute to the nonlinear light absorption in NS under pulsed excitation, are reviewed.
LBO optical parametric oscillator pumped by second harmonic of a Nd:YAG laser
Author(s):
Razvan V. Dabu;
Constantin G. Fenic;
Aurel Stratan;
C. Luculescu;
G. L. Muscalu
Show Abstract
We describe a pulsed doubly resonant LiB3O5 (LBO) optical parametric oscillator (OPO) pumped with a frequency doubled Q- switched Nd:YAG laser amplifier. The threshold power density near degeneracy was found to be 29 MW/cm2. The OPO was continuously tuned from 970 nm to 1175 nm by rotation of the LBO crystal. The linewidth of the signal radiation at 998 nm, and idler radiation at 1136 nm wavelength, were found to be 10 nm, and 13 nm respectively. The OPO output pulse energy of signal and idler near degeneracy was 1.51 mJ for 18 mJ pump energy.
Resonatorless optical bistability in a thin semiconductor film
Author(s):
S. L. Gaivan;
P. I. Khadzhi
Show Abstract
A theoretical investigation is reported of steady-state nonlinear transmission of resonant laser radiation by a thin semiconductor film under the conditions of two-pulse generation of excitons and biexcitons. The equations of state are derived for the description of bistable behavior of the amplitudes of the transmitted pulses and of the quasiparticle concentration, depending on the parameters of the exciting fields. The criteria of existence of an optical bistability are determined.
Nonlinear transmission of ultrashort light pulses by a thin semiconductor film in the exciton range of the spectrum
Author(s):
P. I. Khadzhi;
S. L. Gaivan
Show Abstract
A study is reported of the influence of the saturation of the dipole momentum of an exciton transition on transient transmission of ultrashort laser pulses by a thin semiconductor film in the exciton range of spectrum. It is shown that when rectangular pulses of resonant laser radiation are incident on the film, a threshold-type qualitative change in the transmission by the film takes place from almost total reflection at low level of excitation to complete bleaching at high values of the incident pulse amplitude. An analog of the McCall-Hahn area theorem is derived for ultrashort pulses interacting with the film. When the nonlinear parameter is large, the dependence of the area of a pulse transmitted by the film on the area of an incident pulse becomes multivalued.
Cryptographic mixing transformations for image applications
Author(s):
Adriana Vlad;
Mihai Petru Mitrea
Show Abstract
Several image encryption methods have been recently considered. This paper presents a new image enciphering method starting from the mixing transformations suggested by C.E. Shannon for natural language. There are two ways in which images are involved here: first, as a means of visual perception of the mixing transformation features (the very sophisticated diffusion and confusion); secondly, as the application field itself. Both the theoretical and experimental aspects pointed out here show the high quality of this method of image enciphering. The method illustrates were made either for simulated images with different probability laws and autocorrelation functions, or for natural images.
Characterization of the silicon guided-wave optical couplers and Mach-Zehnder interferometers
Author(s):
Niculae N. Puscas;
Gabriel Nitulescu;
Valentin V. Gherman;
Adrian N. Ducariu
Show Abstract
In this paper we report some experimental results concerning the characterization of the silicon guided-wave optical directional couplers and asymmetrical Mach-Zehnder interferometers from the transmitted spectrum in the 1480 - 1620 nm wavelength region. The experimental results were used for the evaluation of several parameters which define the above mentioned devices, like: the power coupling ratio, the perfect coupling length, the effective interaction length increment and the effective refractive indices, respectively. First, the experimental data were smoothed and fitted by a fourth order function in the case of waveguide directional couplers and a cosine type function in the case of asymmetrical Mach-Zehnder interferometers, respectively. Then, the evaluation of the above mentioned parameters was performed using the least-square method.
Holographic interferometry study of interphase mass transfer
Author(s):
Levai Stefan;
Anicuta Guzun-Stoica;
Mona Kurzeluk
Show Abstract
Interfacial turbulence is investigated experimentally by microscope observations and holographic interferometry with double exposure for the system glycerol-acetic acid-n-butyl- acetate. This system exhibits organized interfacial activity upon transfer of acetic acid from glycerol phase to acetate phase. This behavior was confirmed by the microscope observations in transmitted light. For the holograms obtained the deviation of the fringes between the two exposure times can be related with the changes in the concentration profiles near the interface. Because of the complexity of the phenomenon investigated, the present study is only qualitatively.
Nonlinear processes in laser radiation absorption on metallic surfaces
Author(s):
Marcela Ursache;
Violeta Calian;
Margareta Socaciu;
Cristian Sarpe-Tudoran
Show Abstract
We performed both experimental and theoretical studies on the laser radiation absorption coefficient of a copper surface. A theoretical model for the computation of the absorption coefficient was elaborated for two-layer case (metal-oxide), taking into account the nonlinear processes which govern the dynamics of the temperature and of the widths of the layers. The experimental data and the simulation results proved to be in a very good agreement.
Construction of the first-order stochastic nonlinear differential equations in the modeling of stimulated scattering of optical fields
Author(s):
Vasile D. Babin;
Maria Grigore;
Laurentiu Cojocaru;
Simion Ersen;
Adrian Moldovan
Show Abstract
In this work we use a technique inspired by the inverse problem in the scattering theory, that is, the calculation of partial derivatives along the characteristic directions of the D'Alembert solution of the wave equation (Maxwell and Euler). In this way, we construct a system of stochastic non-linear differential equations. The analysis of this system, using algebraic invariants, gives more information in comparison with that given by Ghelfand-Levitan-Marcenko, in the inverse problem in the scattering theory.
Fidelity evaluation of the conjugated wavefront in photorefractive crystals using direct spatial phase demodulation of optical interferograms
Author(s):
Valentin I. Vlad;
Adrian Petris;
Angela Jianu
Show Abstract
Conjugated wavefront fidelity has been evaluated using an interferometer with a phase conjugate mirror and fringe pattern computer processing. The quantitative interpretation of the fringe patterns is performed using direct spatial phase reconstruction methods (in the space and Fourier domain). A set of algorithms for fast and accurate phase evaluation, by fringe pattern processing, were derived. The result of optical interferograms evaluation appears in terms of different phase representations. These methods have been verified by studies of the optical phase conjugation fidelity in photorefractive crystals.
Talbot moire deflectrometry with direct spatial reconstruction of optical phase
Author(s):
Angela Jianu;
Adrian Petris;
Carmen Popa;
Dragos Popa;
Valentin I. Vlad
Show Abstract
Improvements in Talbot-moire deflectometry are presented. A Talbot-moire interferometer, using a laser diode as light source, a single grating and a CCD camera, placed in one of the Talbot planes, was set-up. The computer yields a moire pattern by mixing the acquired Talbot image of the first grating with the reference generated by computer or stored as an undisturbed external grating Talbot image. For moire pattern processing, direct spatial reconstruction of optical phase, in spatial and Fourier domains, implemented in a high-level image processing language (IDLTM), was employed. The theoretical limit of the relative error of Talbot-moire deflectometry was verified by measuring the focal length of a lenticular system with controlled-focal- length.
Competitive processes in a nonisothermal plasma by deconvolution of low-intensity spectral lines
Author(s):
Iancu Iova;
Gheorghe Ilie;
M. Bazavan;
Costel Biloiu;
Ion Gruia;
Ionel Chera;
M. Cristea;
T. Constantinescu
Show Abstract
The paper presents a data processing algorithm, based on a deconvolution technique that enables the recovery of the low intensity spectral lines, in connection with the analysis of the radiative mechanisms from the non isothermal plasma of a hollow cathode discharge. This method represents a useful tool in the study of the radiative competitive processes involved in the selective excitation mechanisms for UV and visible spectral line's emission. It permits the evaluation of the second kind collision's weight in conjunction with the concentration of the plasma ions for different discharge parameters.
Formation of nonlinear optical MQD (metal quantum dot) in waveguides and modification by high-power laser irradiation
Author(s):
Giancarlo Battaglin;
E. Borsella;
Giovanna De Marchi;
Francesco Gonella;
G. Mattei;
Paolo Mazzoldi;
Alberto Quaranta
Show Abstract
Light waveguides were obtained by ion-exchange process in soda- lime glasses. Metal nanoclusters were subsequently formed in waveguides by either low-mass ion irradiation, at energies of 20 - 2000 keV, or by heating in hydrogen atmosphere at temperatures varying in the range 100 - 250 degree(s)C. Nanoclusters modification induced by pulsed laser irradiation were investigated. The materials were characterized by secondary ion mass spectrometry and nuclear techniques, such as Rutherford backscattering spectrometry, to determine concentration depth-profiles, and by transmission electron microscopy for the nanoclusters detection and size evaluation. Optical analyses were performed to evidence linear and nonlinear properties.
Optical pumping via a velocity-selective state
Author(s):
Norbert Leinfellner;
Laurentius Windholz;
Igor E. Mazets
Show Abstract
We present a new scheme of sub-Doppler laser cooling for atoms used in atomic frequency standards, particularly for 40Ca. We perform calculations concerning optical pumping via a velocity- selective state based upon velocity-selective coherent population trapping. Optical pumping on the Raman transition 41S0- 41P1-31D2 leads to population of the metastable singlet state followed by a decay into the metastable triplet state 4P1. The momentum distribution of atoms in that state (with a half-maximum width of about one corresponding photon recoil momentum) is a direct replica of the distribution of atoms in the 3D2 state.
Linear and nonsaturating effects in atomic multiplets subjected to three strong electromagnetic fields of resonance
Author(s):
F. F. Popescu;
F. Marica;
G. Radu
Show Abstract
Analytic steady-state solutions of the density-matrix equation are discussed for multilevel spin systems in dilute paramagnetic solids at high temperature and subjected to three frequency- correlated fields at resonance. Unlike the double resonance, in the case of triple resonance, when the three microwave fields are sufficiently strong and the spectroscopic bridge conditions are satisfied, important linear and nonsaturating effects are predicted.
Spectroscopy of Yb3+ codoped Pr3+:YAG laser crystals
Author(s):
Aurelia Lupei;
Voicu Lupei;
A. Petraru
Show Abstract
The sensitization with Yb3+ of other rare earth ions emission is intensively used in the last years for increasing excitation efficiency of infrared (diode laser) pumped solid state lasers. It proved as a good sensitizer for Pr3+ emission in various matrices. The spectral investigations for the elucidation of the nature of multisite structure of Pr3+ in YAG and of the Yb3+ co-doping on Pr3+:YAG are presented in this paper. In Pr3+:YAG two types of multisites have been observed: perturbed Pr3+ sites by nonstoichiometric defects and strongly coupled Pr3+ - Pr3+ near neighbor pairs. Pr3+ spectra in Yb3+, Pr3+:YAG show new lines assigned to near neighbor Pr3+ - Yb3+ pairs and Pr3+ - Yb3+ - Yb3+ triads.
Effects of resonant electron-phonon interactions for RE3+ ions in laser crystals
Author(s):
V. N. Enaki;
Aurelia Lupei;
Voicu Lupei;
C. Presura;
V. E. Ciobu
Show Abstract
This paper presents a theoretical treatment of electron-phonon interaction problem in the case of quasi resonant interaction for rare earths ions in laser crystals. Expressions for the absorption or emission lineshapes (asymmetries or splittings of zero-phonon lines) are obtained. The theory is applied to explain some spectral features of Yb3+ transitions in YAG; it allows also the estimation of the vibronic coupling strengths, phonon energies and the `unsplit' electronic levels. A new electronic energy level scheme of Yb3+ in YAG is proposed.
Laser photoacoustic detection of the essential oil vapors of thyme, mint, and anise
Author(s):
A. M. El-Kahlout;
M. M. Al-Jourani;
M. I. Abu-Taha;
Derek C. Laine
Show Abstract
Photoacoustic studies of the vapors of the essential oils of thyme, mint and anise have been made using a line-tunable waveguide CO2 laser in conjunction with a heat-pipe type of photoacoustic vapor sample cell operated over the temperature range 20 - 180 degree(s)C. Identifying spectral fingerprint features are found in the 9 - 10 micrometers spectral region for each of the three essential oils investigated. The principal features of the photoacoustic spectrum of each essential oil are associated with the dominant chemicals present i.e. thymol in thyme oil, menthol in mint and anethole in anise.
Coherent Raman scattering on light-induced optical gratings prepared by adiabatic population transfer
Author(s):
Norbert Leinfellner;
Laurentius Windholz;
Igor E. Mazets
Show Abstract
We investigate theoretically a process of coherent Raman scattering in a medium where the coherence between two low- energetic levels is presented by adiabatic population transfer. In the present case the light induced moving optical grating can be formed by a periodical sequence of solitary-type waves (adiabatons). The parameters of this grating (propagation velocity, coefficients of spatial Fourier decomposition) are controlled completely by the amplitudes and phases of the two coupling fields at the medium entrance.
Energy transfer processes in Cr3+, Nd3+:YAG
Author(s):
Aurelia Lupei;
Voicu Lupei;
A. Petraru;
M. Petrache
Show Abstract
The effects of co-doping with Cr3+ on the absorption and emission characteristics of double doped Cr3+, Nd3+:YAG (yttrium aluminum garnet) are analyzed. The multisite structure due to co-doping (samples with a large range of Cr3+ content were used) is separated from that in single doped crystals. At least seven new lines have been separated in high resolution spectra and a tentative assignment in terms of structural data is proposed. These data suggest that the energy transfer data should be analyzed in terms of inhomogeneous system. However, the measurements indicate strong migration effects. The global donor and acceptor data at 300 K show a linear dependence on donor concentration, but the decays cannot be described in terms of published theoretical models.
Infrared photochemistry of trichloroethylene in the presence of oxygen
Author(s):
Costica Ungureanu;
M. Ungureanu
Show Abstract
Trichloroethylene with added molecular oxygen was photolyzed with a TEA CO2 laser radiation, at v4 (933 cm-1) fundamental vibrational band for C2HCl3 and at v3 (1020 cm-1) fundamental vibrational band for C2DCl3. The stable final products in the infrared multiphoton dissociation of trichloroethylene were determined by mass spectrometry in the 0.5 - 10 Torr pressure range of the gas. After the photodissociation process, the following final products appeared: HCl (or DCl), C2Cl2, C2Cl4, C2Cl4O, CO, Co2 and C2O3. Experimental measurements were also performed to obtain information about the dependence of the specific dissociation rate versus laser pulse energy, for both isotopic species of trichloroethylene.
Excited xenon(1s4) atom detection by modulation laser absorption spectroscopy
Author(s):
Yosuke Sakai;
M. A. Bratescu;
Geavid Musa;
Kenji Miyamoto;
M. Miclea
Show Abstract
A study on the space distribution of the excited xenon atoms on level 1s4 in a d.c. discharge in neon-xenon mixture is presented in this paper. The relative density of the excited xenon atoms was measured using diode laser absorption at 828.239 nm, corresponding to the xenon transition between 1s4 and 2p5 levels. A comparative analysis of the laser absorption signal and corresponding optogalvanic signal, permitted us to define a new parameter, namely optogalvanic effect efficiency, EffOG, as the size of the optogalvanic signal corresponding to an atom optically pumped by laser.
Multiphonon transitions and heating effects in Er:YAG laser rods
Author(s):
Serban Georgescu;
Voicu Lupei
Show Abstract
In this paper we discuss the heat produced by the non-radiative (multiphonon) transitions in Er:YAG laser rods, during the optical pumping, using the mathematical modeling. Three energy transfer processes (up-conversion from 4I15/2, up- conversion from 4I13/2, and cross-relaxation from 4S3/2) are included in the rate equations. The main result of our simulation is that for usual optical pump conditions (Xenon flash-lamp, pumping pulse duration 200 - 300 microsecond(s) ) more than 50% of the absorbed energy is lost as heat in the active medium and only a small fraction (approximately 1%) is lost as fluorescent emission.
Determination of phase transitions in liquid crystals by optical absorption spectroscopy
Author(s):
Cristian Sarpe-Tudoran;
Margareta Socaciu;
Marcela Ursache;
Johny Neamtu;
G. Bratulescu;
S. Radu
Show Abstract
Some interesting experimental results involving new synthesized liquid crystals, derivatives of 4,4'-dihidroxyazobenzene and 4,4'-dihidroxy-azoxybenzene inferred by means of optical absorption spectroscopy are exposed. The absorption spectra dependence on the sample temperature in both heating and cooling processes is investigated. At the same time, the optical density is recorded at a fixed wavelength and it presents significant variations at phase transition temperatures. These data complete the results correlated with mesomorphism, obtained by classical techniques (DTA and microstructural analysis in polarized light).
Photoluminescence decay in porous silicon films
Author(s):
I. Baltog;
M. L. Ciurea;
Gabriela Pavelescu;
L. Mihut;
M. Baibarac
Show Abstract
The photoluminescence (PL) decay measurements were performed on porous silicon films. It was observed that the two components of PL, one of them fast (ns) and the other slow (microsecond(s) or ms sometimes) have different contributions to PL signal, depending on the wavelength of the excitation light. The slow component of PL was in details investigated. Time decay cures for different excitation (337.1 nm, 470 nm, and 550 nm) and emission (550, 650, 700, 800 and 860 nm) wavelengths and also for different excitation intensities were taken. All decay curves were fitted with a stretched exponential. The slow component of PL was proposed to be attributed to the radiative recombination on surfaces.
Photoacoustic detection of ethylene released by biological samples under stress conditions
Author(s):
Simona M. Cristescu;
Dan C. Dumitras;
Doru C. A. Dutu
Show Abstract
A high sensitive photoacoustic system has been developed to monitor the ethylene released by mature tomatoes and wheat seeds during germination as a response of fast effects of mechanical and thermal stress. Under normal conditions of temperature and pressure, the coronet removal yielded a significant increase of ethylene emission as compared to the local wounding of tomato tissues. To determine the temperature influence on ethylene emission rates, both tomatoes and germinating wheat seeds were investigated at cold treatment (4 degree(s)C) and at room temperature (22 degree(s)C). Early changes in ethylene released after imbibition in connection with the physiological results of germination were also monitored.
Luminescence properties of some double-activated zinc-sulphide-type phosphors
Author(s):
Elisabeth-Jeanne Popovici;
Maria Aneculaese;
Veronica Ursu
Show Abstract
Silver and copper double activated phosphor samples were synthesized from zinc sulphide prepared by thiosulphate method and with a NaCl-MgCl2 mixture as flux. The thermal treatment was performed in a protective atmosphere at 900 - 1100 degree(s)C. The samples were characterized by crystalline structure (XRD patterns) and luminescent properties (emission spectra, decay curves). An intensification effect of the copper green fluorescence by silver ions was put in evidence. Conditions for a good green emitting phosphor were established.
Correlation of some radiative processes resulting from electronic and vibrational spectra of a CN molecule excited in an electric arc discharge
Author(s):
Iancu Iova;
M. Bazavan;
Costel Biloiu;
Gheorghe Ilie;
M. Bulinski
Show Abstract
The molecular vibration temperature of the plasma from an interrupt arc discharge in air at atmospheric pressure and at current intensities in the range of 2 divided by 8 Amperes, using electronic and vibration bands of violet [B2(Sigma) + - X2(Sigma) +] and red [A2(Pi) - X2(Sigma) +] systems of the CN molecule was determined. At the equilibrium temperature of 6400 K, 27 lines of Ti, contained as impurity in coal electrode were found. These spectral lines were found in the 247 divided by 340 nm spectral range, having the upper levels of the excitation energies in the 3.60 divided by 5.69 eV range, in the neighborhood of the energy of dissociation of the CN molecule on the fundamental electronic state. Some considerations about the vibrational states populations are also made.
Laser-based assessment of lipid peroxidation in humans
Author(s):
Gianfranco Giubileo
Show Abstract
Infrared absorption spectroscopy can be performed at very high resolution by tunable diode laser (TDL) based optical systems for any gas with well resolved absorption spectra. In a double beam setup atmospheric trace gas concentration can be measured down to ppb levels. The analysis of trace gases may have useful applications in detecting chemicals in the human breath for non invasive medical diagnostic. The capability of TDL based breath analysis was well demonstrated by monitoring ammonia and methane. In the human body the formation of free radicals does induce oxidative degradation of polyunsaturated fatty acids (lipid peroxidation) which is a damage for cells and organs in the organism. Specific volatile hydrocarbons generated as end product by lipid peroxidation (LP) can be found inside circulating blood and expired breath. TDL based analysis of those specific hydrocarbons (ethane and pentane) in the expired breath can allow a non invasive assessment of the LP extent.
CO2 laser ablation of biological tissue
Author(s):
Dan C. Dumitras;
Doru C. A. Dutu;
Consuela-Elena Matei
Show Abstract
This paper presents a comprehensive review of the CO2 laser ablation of biological tissue. Based on energy balance for modeling laser ablation, the thermal relaxation time and the ablation threshold are determined. Laser ablation of biological tissue is related to the spatial coherence of laser beams, so that the propagation of laser beams, the beam quality and the focusability of laser beams are taken into consideration. To achieve the ablation threshold, the laser irradiance in the focal zone is computed as a function of laser parameters. The advantages of pulsed operation of the CO2 laser for minimum residual thermal damage of the tissue are stressed. The strengths and the weaknesses of the CO2 laser ablation are finally discussed.
Laser method for corneal structure investigation
Author(s):
Mihail-Lucian Pascu;
Benone D. Carstocea;
Gheorghe Popescu;
Otilia L. Gafencu;
Silvia Apostol;
N. Moise;
Miruna Roman;
C. M. Ticos
Show Abstract
This paper reports a laser method for corneal structure investigation which allows to obtain images of corneal layers as well as information about dimensions of the endothelium and basal epithelium cells. The method's principle is based on the laser radiation reflection at the interface between ocular media having different refractive indices. So, the laser incident beam on the cornea is multiply reflected and refracted within it, since the cornea is a superposition of several transparent layers with different refractive indices. If observed on a screen, the radiation reflected by a certain corneal layer forms on it the image of corneal cell structure. Because of cornea curvature, the reflected beam which contains information about corneal structure--becomes strongly divergent; therefore the experimental set-up forms the cell images big enough to be seen directly by eye.
Electronic-beam analysis of excimer lasers used for photorefractive keratotomy
Author(s):
Carlos B. Roundy
Show Abstract
Excimer lasers are an excellent instrument for performing photorefractive keratotomy, PRK. The UV light from the laser causes an ablation of the cornea in proportion to the intensity of the light. The primary characteristic essential to successful PRK is the uniformity of the Top Hat, or working portion of the laser beam. In order for this intensity profile to be sufficiently uniform for PRK, it is essential to periodically measure the equality of the laser beam profile. This ensures that the laser continues to operate properly and provide the expected performance.
UV laser radiosensitivity of normal and tumoral chromatin
Author(s):
Liliana Radu;
Ion N. Mihailescu;
V. Preoteasa;
Irina Radulescu;
Doina Gostian;
Alexandru Hening;
S. Radu
Show Abstract
A normal and a tumoral chromatin radiosensitivity to an UV laser radiation was determined. The characteristics of these chromatin samples were established by the analysis of the absorption and emission spectra of chromatin complexes with a specific DNA ligand-ethidium bromide, by Scatchard representations of ligand binding to chromatin and by the Forster energy transfer efficiency determination between two fluorescent ligands coupled at chromatin: dansyl chloride and acridine orange. The effects of excimer laser beam with (lambda) equals 248 nm on chromatin structure were analyzed by the above methods and also by the establishment of the intrinsic chromatin fluorescence and of the excited state lifetimes of a specific DNA ligand.
Influence of the laser beam wavelength on the gonoarthrosis treatment: a preliminary comparative study
Author(s):
Gabriela Brojbeanu;
S. Suteanu;
Mircea V. Udrea;
Virgil V. Vasiliu
Show Abstract
A comparative study on four groups of patients which have been exposed to laser radiation was performed. Three wavelength were used (633, 670 and 830 nm). The fourth group received only laser placebo. Every group is composed by 20 people homogeneously selected from the point of view of age, sex and clinical and paraclinical parameters. The irradiation dose was kept almost the same, i.e. 15 J/cm2. The dependence of subjective and objective indicators on the laser wavelength were put into evidence.
Value of low-power lasers in the treatment of symptomatic spondilosis
Author(s):
Ciprian Antipa;
Vladimir Moldoveanu;
Nicolae Rusca;
Ion I. Bruckner;
Mihaela Vlaiculescu;
Elena Ionescu;
Virgil V. Vasiliu
Show Abstract
Low power laser (LPL) use in the treatment of arthrosic rheumatism is well known. From a total number of 280 patients with symptomatic spondylosis we finally selected 66, with changes of the EEG color mapping. These investigation was done before and after treatment in order to obtain an objective method to appreciate these results. The patients were splitted in laser group (36 patients treated with HeNe and IR diode LPL) and control group (30 patients treated with placebo laser). The results indicate a significant improvement of the symptoms at 77% of the patients from laser group as compared with 33% favorable results at the placebo laser. The EEG mapping improved at 58% patients from laser group as compared with 20% at the control group.
Comparison of the effect of UV laser radiation and of a radiomimetic substance on chromatin
Author(s):
Irina Radulescu;
Liliana Radu;
Ruxandra Serbanescu;
V. D. Nelea;
C. Martin;
Ion N. Mihailescu
Show Abstract
The damages of the complex of deoxyribonucleic acid (DNA) and proteins from chromatin, produced by the UV laser radiation and/or by treatment with a radiomimetic substance, bleomycin, were compared. The laser radiation and bleomycin effects on chromatin structure were determined by the static and dynamic fluorimetry of chromatin complexes with the DNA specific ligand-- proflavine and by the analysis of tryptophan chromatin intrinsic fluorescence. Time resolved spectroscopy is a sensitive technique which allows to determine the excited state lifetimes of chromatin--proflavine complexes. Also, the percentage contributions to the fluorescence of proflavine, bound and unbound to chromatin DNA, were evaluated. The damages produced by the UV laser radiation on chromatin are similar with those of radiomimetic substance action and consists in DNA and proteins destruction. The DNA damage degree has been determined. The obtained results may constitute some indications in the laser utilization in radiochimiotherapy.
Laser therapy in ocular tumors
Author(s):
Benone D. Carstocea;
Otilia L. Gafencu;
Silvia Apostol;
Marcel A. Ionita;
A. Moroseanu;
Traian Dascalu;
Voicu Lupei;
V. Ionita-Manzatu
Show Abstract
The medical laser equipments made at NILPRP have been exploited intensively for more than 10 years at CMH. The availability and reliability of the first like-on equipment have increased, following improvements in optical delivery system and cooling circuit. This paper shows the impact of technical advances on the development of ophthalmologic laser therapy. Intraocular tumors pose special problems of diagnosis and treatment. Diagnostic methods include addition to systemic and ophthalmologic examinations, ancillary examinations, such as transillumination, fluorescence angiography, ultrasonography, radioactive phosphorus uptake tests, radiology, computerized tomography and fine-needle aspiration biopsy with cytological analyses. The enucleation of the involved eye used to be a generally accepted management of malignant tumors. Improved therapeutic methods such as photocoagulation and better surgical techniques now provide a variety of therapeutic alternatives. This study covers 31 cases of intraocular tumors that were managed either by Argon Laser photocoagulation and/or by Nd:YAG laser surgical treatment. Four cases were intraocular metastasse and 17 cases were primitive intraocular tumors. Argon laser therapy proved to be totally ineffective for intraocular metastasse but very adequate therapy for primitive tumors. Tumor extirpations (choroidal, cillary body or iris tumors) using Nd:YAG laser lancet proved to be more suitable than classic surgery.
Laser-induced fluorescence of atherosclerotic plaques
Author(s):
N. Moise;
Mihail-Lucian Pascu;
C. Carp;
C. Volvoreanu
Show Abstract
In vitro laser-induced fluorescence (LIF) spectra and lifetimes of normal and atherosclerotic tissues are reported. The experimental arrangement conceived to measure LIF contained a 700 ps nitrogen pulsed laser (337.1 nm) and two quartz optical fibers to induce and respectively collect the fluorescence of normal and diseased samples. With UV laser excitation we found proeminent differences both in spectral and temporal range between normal artery and atherosclerotic plaques which was standard pathological classified in five types such as: normal artery, fibrous plaque, atherosclerotic plaque, calcified plaque and ulcerated plaque. As for statistics, the total number of measurements performed on each of the five mentioned types of tissues was 25.
Determination of size-shape distribution of biological particles from light scattering measurements
Author(s):
Niculae E. Mincu;
Maria-Ana Popovici;
Mara Dobre
Show Abstract
We present static light scattering measurements of size-shape distributions of biological particles in suspension. Results are compared to the Rayleigh-Debye-Gans theory predictions. They are inverted to retrieve the geometrical parameters of the suspended particles and their size-distribution function. The inversion of data is performed by a combined method using normalized cubic B spline functions and linear programming, which is firstly applied to different sets of simulated data, to study its efficiency and stability in the presence of experimental noise.
Photodynamic therapy using hematoporphyrin derivative and He-Ne laser irradiation in Erlich tumor: an experimental study on mice
Author(s):
Mihaela Radu;
D. Ciotaru;
Mihaela A. Calin;
G. Savi;
M. Bota;
Carmen Stroila
Show Abstract
In vitro (absorption spectroscopy) and in vivo (fluorescence microscopy) studies before and after the uptake of intraperitoneal injected Hematoporphyrin Derivative (HpD) were made in mice. The absorption spectrum of HpD is characterized by four bands in the visible region with decreasing absorption towards longer wavelengths (510 nm, 540 nm, 568 nm and 621 nm). These spectra were obtained only at low concentration (10-5 M). After (15 - 30) minutes postirradiation (He-Ne laser, 1 mW) the features of curves were the same with those of nonirradiated samples but with a deplacement of wavelengths. The presence of laser emitting products was pointed out by fluorescence microscopy (cryostat section in fluorescence microscopy).
Comparative study of the thermal effects generated by laser irradiation for medical applications
Author(s):
Mihaela A. Calin;
M. Tomescu;
Roxana N. Radvan;
Mihaela Radu;
Teodor Necsoiu
Show Abstract
The medical laser applications use the thermal effects of laser irradiation. The present work contains applications of the thermovision. This method offers the following advantages recording and processing of the thermal distribution on the irradiated zone. The study has in view the development of an algorithm of work for an useful data base regarding the laser application in medicine. The experiments used Ar laser, laser diode and some kinds of biological tissues. The paper presents some thermal distributions before, during and after laser irradiation and the images processing.
Low-power laser efficacy in peripheral nerve lesion treatment
Author(s):
Ciprian Antipa;
Mihaela Nacu;
Ion I. Bruckner;
Daniela Bunila;
Mihaela Vlaiculescu;
Mihail-Lucian Pascu;
Elena Ionescu
Show Abstract
In order to establish the low energy laser (LEL) effects on nervous tissue regeneration in clinical practice, we evaluated in double blind, placebo controlled study, the efficacy of LEL in the functional recovery of 46 patients with distal forearm post- traumatic nerve lesion, after surgical suture. The patients were divided into two groups: A-26 patients were treated with LEL; B- 20 patients, as control, were treated with placebo lasers and classical medical and physical therapy. Lasers used were: HeNe, 632.5 nm wavelength, 2 mW power, and GaAlAs diode laser, 880 nm wavelength, pulsed emission with an output power about 3 mW. Before, during and after the treatment, electromyography (EMG) and electroneurography (ENG) were done in order to measure objectively the efficacy of the treatment. We obtained good results after 4 - 5 months at 80.7% patients from group A and about the same results at 70% patients from group B, but after at least 8 months. The good results were noticed concerning the improvement of EMG and ENG registrations and on the involution of pain, inflammations, movements and force of the fingers. Finally we can say that the favorable results were obtained in at least half the time with LEL treatment faster than with classical therapy.
Low-power laser use in the treatment of alopecia and crural ulcers
Author(s):
Tavi Ciuchita;
Mircea Usurelu;
Ciprian Antipa;
Mihaela Vlaiculescu;
Elena Ionescu
Show Abstract
The authors tried to verify the efficacy of Low Power Laser (LPL) in scalp alopecia and crural ulcers of different causes. Laser used was (red diode, continuous emission, 8 mW power, wave length 670 nm spot size about 5 mm diameter on some points 1 - 2 minutes per point. We also use as control classical therapy. Before, during and after treatment, histological samples were done for alopecia. For laser groups (alopecia and ulcers) the results were rather superior and in a three or twice time shorter than control group. We conclude that LPL therapy is a very useful complementary method for the treatment of scalp alopecia and crural ulcers.
Applications of infrared heterodyne detection systems
Author(s):
Marek Strzelec;
Zbigniew Puzewicz;
Miroslaw Kopica
Show Abstract
This paper presents the theoretical and practical solutions of infrared, heterodyne detection systems applied in the pollution monitoring, methane detection, industry as well as laser spectroscopy. The utilization of stabilized laser diodes, coherent pumped solid state lasers as well as CO2 lasers with conversion of generation frequency covers the broad band of infrared region especially interesting for detection of different atmosphere pollutants or gas contaminants. Low cost heterodyne vibrometers, velocimeters or rangefinders can find wide industrial or metrological applications.
Characterization of integrated optical waveguides based on oxidized porous silicon
Author(s):
M. Balucani;
V. Bondarenko;
N. Kasuchits;
G. Lamedica;
N. Vorozov;
A. Ferrari
Show Abstract
Integrated optical waveguides based on oxidized porous silicon were fabricated by means of traditional silicon technology. Near- field pattern and out-of-plane scattering losses were measured to characterize optical properties of the waveguides. Strong confinement of light within the core of the waveguides as well as optical losses of about 5 dB/cm have been demonstrated in the visible range. The achieved results make the waveguides promising in optoelectronics use.
Electronic laser beam profile measurement
Author(s):
Carlos B. Roundy
Show Abstract
Because the spatial beam structure is the most critical element of a laser, measurement of this beam structure is indispensable in laser design, development, and manufacture. Since measurement of the beam structure inside the cavity is impractical, if not impossible, the beam profile structure outside the laser provides the only real insight into cavity structure. It is critical that profile measurements outside the cavity be as precise and illuminating as possible. Electronic measurement of the output beam profile is the only method that gives sufficiently accurate and illuminating beam structure analysis.
Satellite remote sensing data applied for seismic risk assessment of the Vrancea region
Author(s):
Maria Zoran;
Cora Lucia Braescu;
Cristina Aiftimiei
Show Abstract
The aim of this study is to present the results of the application of remote sensing techniques for seismic risk analysis, which estimates the geographic distribution, frequency, and intensity of seismic activity, without attempting to predict specific events. This method is based on the recognition of the active faults, which are defined as breaks along which movement has occurred in Holocene time (past 11,000 years). Remote sensing analysis and field studies of active faults can provide a geologic history that overcomes many of the shortcomings of instrumental and historic records.
Amorphous silicon photodetectors for optical integrated circuits
Author(s):
M. Balucani;
V. Bondarenko;
G. Lamedica;
A. Ricciardelli;
A. Ferrari
Show Abstract
The first successful attempt to integrate on-chip optical waveguides based on oxidized porous silicon and amorphous silicon photodetectors have been demonstrated. Buried channel waveguides were performed by thermal oxidation of porous silicon. Amorphous silicon photodetectors were fabricated on the waveguides. Different device structures as well as their performance attributes are exhibited. The devices were demonstrated to have photocurrent characteristics promising for optoelectronic applications.
Properties of polymer compositions for recording and copying optical images
Author(s):
Valeriu V. Bivol;
N. A. Barba;
Stephan V. Robu;
B. M. Ishimov;
Lyudmila A. Vlad;
A. M. Prisacari;
G. M. Triduh;
Elen A. Akimova
Show Abstract
In this paper we present the experimental results of the investigation of relief recording of the information with application of the media based on thermoplastic materials and synthesized organic photopolymers. We present also the results concerning the possibilities of strengthening of polymer media with the scope to improve mechanical properties of the relief image (hardness, strength, adhesive stability) and the possibilities to make copies by stamping method. Also we examine the possibility to increase the sensitivity of photothermoplastic media by addition of the injector chalcogenide layers.
Electro-optic response of some chiral liquid crystals with high spontaneous polarization
Author(s):
Constanta Dascalu;
Cornelia Motoc;
Emil Petrescu;
Constantin Rosu;
H. D. Koswig;
U. Labes
Show Abstract
The electrooptical properties of some SSFLC devices with high spontaneous polarization liquid crystals are presented. The switching time was determined as function of electric field strength and a.c. frequency. Using the switching time the rotational viscosity (gamma) $curly phi was determined. The results are explained by considering the spectacular molecular relaxation, known as Goldstone mode. The surface stabilized ferroelectric liquid crystal (SSFLC) devices offer memory (bistable) capability, fast response speed and sharp threshold and have a variety of applications in electronics.
Fluid optical components and their applications in optoelectronics
Author(s):
Roxana N. Radvan;
Mihaela A. Calin;
Roxana Savastru;
Maria Robu;
Mihaela Radu
Show Abstract
This work presents some contribution in the non-conventional optical components field. The idea is concerning to fluid optical components, having in view to elaborate a documentation--like a catalogue of optical fluids--for optical system design. The using of optical fluids represents a new method of attaining apochromatic color correction in refractive optical systems.
Optical fiber multiplexed image transmission system
Author(s):
Sorin Miclos;
Tudor Zisu;
Bogdan Robea
Show Abstract
An optical fiber multiplexed image transmission system can be used in dangerous and low accessible environments, such as in nuclear or high explosion risk environments because the optical fiber cable is insensitive to the electromagnetic disturbances and, when an appropriate optical fiber is used, it withstands the gamma radiation. The system has the capability to simultaneously transmit, by using the video signals switch, the image from four CCD cameras placed in the dangerous environment to a remote surveillance center, at 2 km distance.
Cylindrical piezoceramic transducer for a remote optoelectronic system
Author(s):
Irinela Chilibon;
Maria Robu
Show Abstract
This paper presents an experimental study on the behavior of cylindrical piezoceramic transducers exposed to dynamic mechanical shocks. The piezoceramic materials under study are solid solutions of Pb(ZrxTi1-x)O3 and present direct piezoelectric effect. In the laboratory were made experiments with cylinders of BaTiO3 and PZT ceramics, for determination of their behavior at mechanical shocks. The shocks resistance of piezoceramic materials is essential in those applications that involve dynamic stress. The tests on ceramics have sought to establish the capacity of a piezoceramic element to resist at recurrent hits and to absorb energy.
Optical systems for night vision devices
Author(s):
George Copot;
Rodica Copot
Show Abstract
The paper is the result of the studies made to establish criteria for the designing and the assessment of the optical systems for the night vision devices so that the ratio between the performances and the manufacture costs is best. These criteria were used to check optical systems of the existing night vision devices and to design new optical systems.
Optical beacon for pointing and tracking systems for free-space communications
Author(s):
Paul E. Sterian;
Petre P. Digulescu;
R. V. Ivan
Show Abstract
A bi-directional pointing and tracking system is needed in order to establish the optical link between two optical transceivers located in two separated points at the ground or on satellites. That usually suppose the presence of a separate laser transmitter an optical beacon used for pointing and tracking purposes. The major stages of the pointing and tracking process were analyzed based on a mathematical model presented in references. In order to increase the reliability of optical links a new optical beacon is purposed and, consequently a new pointing and tracking method is developed. This method requires only communication laser transmitters and uses their optical beams for pointing and tracking process, additionally giving the possibility to increase the signal to noise ratio at the communication receiver. A mathematical model of such a system is developed and an analysis of the method is performed.
Laser treatment of a-SiC:H thin films for optoelectronic applications
Author(s):
D. Ghica;
Niculae E. Mincu;
Catrinel A. Stanciu;
Gheorghe H. Dinescu;
E. Aldea;
Viorel Sandu;
A. Andrei;
Maria Dinescu;
A. Ferrari;
M. Balucani;
G. Lamedica
Show Abstract
Amorphous and hydrogenated (a-SiC:H) as well as crystalline silicon carbide are widespread materials for optoelectronic applications. In this paper, we studied the effect of laser/RF plasma jet treatment of a-SiC:H thin films deposited by Plasma Enhanced Chemical Vapor Deposition, on Si wafers. A Nd:YAG laser ((lambda) equals 1.06 micrometers , tFWHM equals 14 ns, E0 equals 0.015 J/pulse) was used with a fluence of 4 mJ/cm2 incident on the sample, the number of pulses being varied. Plasma treatments were performed in a plasma jet generated by a capacity coupled RF discharge in N2. Different analysis techniques were used to investigate the films, before and after the irradiation: X-ray diffraction, X-ray photoelectron spectroscopy and transmission electron microscopy. We followed the modification of their structure and composition as an effect of the laser/plasma treatment. A comparison with the excimer and also with the RF treatments was performed.
Gamma-induced transparency loss of thick quartz fibers
Author(s):
Eldar M. Gasanov;
E. M. Ibragimova;
Bekzad S. Yuldashev;
Mukhsin Kh. Ashurov;
Igor R. Rustamov
Show Abstract
Radiation response of thick multimode Ge, P, F-doped quartz fiber has been examined after exposure to 60Co gamma-source within a dose interval of 10 - 107 Gy at a dose power of 2.3 and 24 Gy/s at 300 K. The induced transparency losses A at the wave length of 1.06 micrometers do not exceed 0.2 after a dose of 106 Gy and reach a saturation, while the fibers are closed for visible light after a smaller dose. Varying focus and an angle of leading a probe light beam in fiber, the core modes were found to close at a dose of 104 Gy due to radiation induced color centers of Ge and non-bridging oxygen O-, and the clad modes were suppressed at 500 Gy by the expense of Al impurity color centers.
Electrical and optical characterization of PbTiO3/Si heterostructures for applications in optoelectronics
Author(s):
V. Dragoi;
Lucian Pintilie;
Ioana Pintilie;
D. Petre;
I. Boerasu;
M. Alexe
Show Abstract
The ferroelectric/semiconductor heterostructures were fabricated by sol-gel deposition of lead titanate (PT) thin films on a single-crystalline p-type Si wafers. The PT films were crystallized by a conventional thermal annealing for 30 min at temperatures ranging from 575 degree(s)C to 675 degree(s)C. Current-voltage and capacitance-voltage characteristics show a hysteresis which can be due to the spontaneous polarization of PbTiO3. The current-voltage characteristics exhibit a diode behavior while the capacitance-voltage exhibits a large memory window, up to 3.5 V, for the films annealed at 600 - 650 degree(s)C. At the illumination with modulated light, a.c. photovoltage was detected on a broad range of wavelengths (0.35 divided by 4 micrometers ) for all samples. The spectral distribution of the photoelectric signal in the UV-Vis- IR domain shows two local maxima. A model is proposed to explain the observed experimental results.
Optical integrated circuits
Author(s):
Ovidiu D. Iancu;
Daniel Pircalaboiu
Show Abstract
The notorious implication of integrated optics in the nowadays communication systems makes more interesting the development of optical integrated devices and circuits. The evolution of the communication systems was sustained by the integrated optics and it is obvious that the actual interests in the optical communications are also transferred and adapted to integrated optics. The presentation of actual state-of-the-art in this field is a good opportunity both for an evaluation on the above mentioned evolution and for discerning the actual trends and their perspectives. These trends, guided by applicative goals, have to be discussed not only from the theoretical point of view but also from a practical one.
Optical properties of polycrystalline InxGa1-xSb (x=0.20) from 15 to 30 um
Author(s):
Cristiana E. A. Grigorescu;
Stefan A. Manea;
Michaela F. Logofatu;
Ion I. Munteanu;
B. Logofatu;
Mihaela A. Calin;
Mihaela Radu;
Mihail F. Lazarescu
Show Abstract
This paper reports on the optical properties of polycrystalline p-type InxGa1-xSb (x equals 0.20) over the wavelength range 15 - 30 micrometers , at room temperature. The material was obtained by direct synthesis from the elements and rapidly crystallized following a particular temperature regime. Transmittance and reflectance measurements were performed at room temperature by using a SPECORD M80 spectrophotometer. From the resulted values we calculated the absorption coefficient (alpha) as a function of the photon energy. Considerations are made concerning the peculiarities involved by the polycrystalline structure and the surface imperfections on the absorption phenomena over the mentioned wavelength range.
Verifying model for statistical hypothesis in detection of noncoherent radiation
Author(s):
Vasile D. Babin;
Simion Ersen;
Adrian Moldovan;
Nicusor Iftimia
Show Abstract
A mode of quantic detection for noncoherent optical radiation as noise limit is presented. Using the representation on coherent state of density matrix operators ((rho) ) and of detection operators ((pi) ), the detection probability (Qd), false alarm probability (Qo) and signal-noise ratio (S/Z), are estimated, as function of the number of freedom degrees of temporal oscillation modes (Mt) and of the spatial oscillation modes (Ms). A validation algorithm of statistical hypotheses, resulted from noncoherent optical field analysis, is made using Newman-Pearson criterion.
Characterization of ion-exchanged waveguides from near-field measurements
Author(s):
Daniel Pircalaboiu;
Gabriella Motta;
Guido Perrone;
Ivo Montrosset
Show Abstract
The refractive index distribution is a key parameter not only to characterize the technological process but also for any integrated optical simulator. In this paper we propose a new algorithm to reconstruct the refractive index profile from the near-field measurements. The technique is based on the matching of the measured intensity profile with a computed one, varying the maximum index change and the diffusion depth.
Non-Markovian effects in dissipative systems
Author(s):
Eliade N. Stefanescu;
Paul E. Sterian
Show Abstract
In a unitary approach generally used in quantum optics, we consider Lindblad's Markovian master equation and the non- Markovian master equation of Ford, Lewis and O'Connell. We show that the second-order master equation in the hierarchy obtained from a Krylov-Bogoliubov expansion corresponds to the Born approximation. By time averaging, and neglecting the rapidly varying terms, Lindblad's master equation is obtained. With these two equations, we calculate the decay spectrum. We find that for rather low dissipated energies, only the non-Markovian master equation provides correct results. Based on the independent oscillator model of the dissipative coupling, explicit expressions of the dissipative coefficients are obtained.
Optoelectronic micropositioning device with a piezoceramic transducer
Author(s):
Irinela Chilibon;
Maria Robu
Show Abstract
This paper presents an experimental study on the behavior of piezoceramics type PZT, having a high compliance, and their application for an optoelectronic micropositioner device with piezoceramic transducer. The piezoelectric ceramics are crystallite conglomerate ferroelectrics materials with random orienting. In the laboratory we have realized PZT ceramics with various additions (Ni, Bi, Mn), presenting high compliance, for optoelectronic micropositioning device in micrometry displacements. The experimental transducers, realized like stacks of 30 divided by 35 pieces of PZT thin disks, supplied with 0 divided by 1000 V voltages, have produced 0 divided by 15 micrometers displacements.
Spectroellipsometric characterization of multilayer systems containing Ni and Bi
Author(s):
V. Hutsanu;
Mariuca Gartner;
Constantin Ghita;
Voicu Dolocan
Show Abstract
In this paper an optical evaluation of the system Ni,Bi/Cu,ITO/glass system, prepared by electrochimical method is presented. Among various factors that affect the optical and structural properties of the multistructure systems we focus on the influence of the substrate and the interfacial oxidic layers. To this end we used the Spectroellipsometric (SE) method in VIS- NIR spectral range. The SE results show that the electrochemical deposited films (Ni,Bi) are porous and their refractive index depends strongly on the substrate.
Orthorectification of radar (SAR) data: synergism and complementariness with optical (Landsat TM) data
Author(s):
Cora Lucia Braescu;
Maria Zoran;
Cristina Aiftimiei;
Axente D. Stoica;
Dan Raducanu
Show Abstract
The integration of digital remote sensing data from either airborne or spaceborne platforms and normal line or thematic maps has become increasingly significant to a varied field of applications, from geology to municipal mapping. To take full advantage of this data source, it must be overlayed to existing map data. The geometry and projection information must be equivalent, in other words they must be an orthogonal projection or correlation between the point on the ground and some reference surface. This process is referred to as rectification. The output satellite or airphoto images are referred to as orthorectified images or ortho images. The particular data we have used--SAR (Synthetic Aperture Radar) have several characteristics which we had to take into account in order to produce the orthorectified images. The main problem is the geometric distortion (layover, shadowing effects) due to the oblique viewing of the antenna. Another problem met was the `speckle' type perturbation, due to the coherence of the radar signal. An orthorectification procedure for radar data (SAR-ERS-1) over a mountainous zone in Romania (Buzau) is presented, also a registration procedure with optical (Landsat TM) data and a complementarity study.
Al2O3 single-crystalline substrates for optoelectronic applications
Author(s):
C. Logofatu;
Brandusa Iliescu;
Ionut Enculescu;
Cristiana E. A. Grigorescu;
Stefan A. Manea
Show Abstract
This paper reports on controlled electric and optical properties of single crystalline sapphire for substrates use. The crystals were grown by the Czochralski method from a graphite crucible by using an original non-conventional crystal growth assembly. We paid a special attention to the homogeneity of the crystal. A new model for the electric conduction mechanisms is considered, the validity of which was confirmed by experimental measurements.
Optical light modulation in planar As2Se3Snx waveguides
Author(s):
Aurelian A. Popescu;
Alexandru I. Albu;
A. Tsaranu
Show Abstract
The modulation of infrared radiation ((lambda) equals 1150 nm) in waveguides of glassy semiconductors As2Se3 and As2Se3Sn0.175 has for the first time been investigated experimentally. The measurement of frequency-response characteristic shows that there are two relaxation constans-fast and slow. The rise time of optical modulator with arsenic selenide waveguides having tin additions is nearly 10-3s. The origin of additional absorption can be explained in the framework of two-steps transition models. The first one is the excitation of excess carriers into the conducting band by highly absorbed pump beam and theirs partial capturing on localized states. The second is the re-excitation of trapped carriers and restoration of optical absorption by signal waveguided beam.
Approximate solutions of the eigenvalue equation near cutoff for TE0m and TM0m modes for a step index fiber optic: new forms and considerations
Author(s):
Carmen Liliana Schiopu;
Paul Schiopu
Show Abstract
In this work the authors intend to present a new approximate technique of solving the characteristic (eigenvalue) equation for a step index fiber optic near cut-off. To illustrate this new method, there are presented (and demonstrated) two particular forms, corresponding to the case v equals 0 (TE0m and TM0m modes). Solutions of these equations are compared with other solutions suggested by Marcuse and--also--it is analyzed the accuracy of our results compared with the general solution of the characteristic equation.
Concept of WDM-HD: WDM for increasing the information capacity of fiber optic communication systems
Author(s):
Paul Schiopu;
Laurentiu Dragnea
Show Abstract
In fiber optic communications the technique of wavelength division multiplexing (WDM) constitutes a means of increasing the information capacity of fiber optics in communication systems and allows the optimal usage of the capacity of optic fiber. This paper presents the concepts of WDM and high density WDM from the point of view of developing a unitary theoretical analysis of necessary parameters for the design of optic integrated circuits with functions for optic signals multiplexing and demultiplexing, with planar diffraction gratings.
Modeling passive and active LiNbO3 optical waveguides
Author(s):
Niculae N. Puscas;
Ion M. Popescu
Show Abstract
Based on several experimental measurements performed on Er3+-doped Ti:LiNbO3 optical waveguides, this paper presents some theoretical and experimental results concerning the refractive-index profile and the absorption spectra corresponding to the transition 4I15/2 yields 4I13/2. The refractive-index profile of the above mentioned waveguide has been determined from near field intensity measurement using an optical fiber. A deconvolution algorithm for the original mode field of the waveguide reconstruction has been expanded and optimized for 2D applications. By using the reported model it is possible to evaluate some parameters which characterize the optical waveguides like: the refractive-index difference (Delta) n and the penetration depth d. The homogeneous absorption and emission cross sections have been calculated from the transmitted spectrum around 1531 nm of the Er3+-doped Ti:LiNbO3 waveguide using the density matrix formalism.
Effective index method for the computation of the propagation constant and electromagnetic field distribution in z-uniform dielectric or semiconductor waveguides
Author(s):
Mihail M. Dumitrescu;
Mircea D. Guina
Show Abstract
The paper presents a numerical implementation of the Effective Index Method (EIM) for the determination of the propagation constants and field distributions in dielectric or semiconductor guiding structures that are uniform on the direction of propagation. The implementation proved to be applicable to a wide range of guiding structures (ridge, buried and diffused guides) and was tested against analytical solutions and against other methods' results proving good accuracy. The advantages and limitations of the EIM are discussed and a common waveguide problem result is presented as an example. From the practical applications of the method, the optical analysis of the ridge geometry and QW positioning of a 3W continuous wave GRIN SCH SQW laser diode in the 670 nm band is briefly discussed and the measured performances of the devices are presented.
Real performance of image intensifier systems for night vision
Author(s):
Marinica Mirzu;
Liviu Cosereanu;
Mihai Jurba;
George Copot;
Daniel Ralea;
Raluca-Maria Marginean
Show Abstract
The detection model based on the fluctuation theory can determine only the upper limit in the performance of image intensifier systems for night vision. Our laboratory and field experiments show that the signal to noise ratio of the final image is influenced by the fluctuations in the number of incident photons on the image intensifier photocathode, the quantum efficiency of the photocathode, the value of noise generated in the amplification process and the modulation transfer function for the atmosphere and optical components.
Control of laser spiking in Nd:YAG lasers with saturable absorbers
Author(s):
Mihai Jurba;
Vasile D. Babin;
N. Baltateanu;
Ion Gherghina;
V. Jipa;
E. Popescu;
Liviu Cosereanu;
Marinica Mirzu
Show Abstract
Spiking behavior can be analytically described using laser rate equations. Control or suppress of spiking behavior can be obtained by placing suitable absorbers in the laser cavity. LiF:F2- saturable absorbers obtained by electron irradiation of LiF crystals were employed in control of laser spiking of pulsed Nd:YAG lasers. Experimental results are in good concordance with theoretical values.
Optical transmission of ZnO thin films
Author(s):
Ioan I. Rusu;
Ionel V. Bursuc;
Ioan Vascan
Show Abstract
ZnO films were prepared by d.c. reactive cathodic sputtering in a planar magnetron. The structural properties of d.c. planar magnetron sputtered ZnO films are studied as a function of deposition parameters: substrate type, substrate temperature, sputter gas pressure, growth rate and sputtering power. ZnO films growth has been carried out in an oxygen and argon atmosphere. In dependence on the O2 partial pressure in the argon sputtering gas there exists a narrow process window around a po/(pAr+po) ratio of 5 - 10% which yields transparent, low- resistance layers. The discharge voltage dependence on the oxygen partial pressure is a sensitive indicator for the oxidation state of the target surface and can be used for the regulation of the deposition process. Lower O2 partial pressures yield metallic-like, opaque, but highly resistant layers. Higher oxygen partial pressures lead to transparent but highly resistant ZnO layers. Layers of lowest resistivity (5 X 10-4 (Omega) cm) and highest optical transmission (90%) have a stoichiometric ratio Zn:O of 1.0 and exhibit the largest grains. These films are applied as piezoelectric transducers in micromechanical sensors and actuators.
Magneto-optical behavior of ferronematics
Author(s):
Cornelia Motoc;
Emil Petrescu;
Constanta Dascalu
Show Abstract
The behavior under magnetic fields of new types of ferronematics is examined. First, by using both optical and electrical method, an increase in the critical field for Freedericksz transition was noticed in cells containing ferronematics. Second we give an explanation of the relaxation processes occurring in ferronematics when the magnetic field was suddenly varied. When ferronematics are involved, the relaxation phenomena are described by lower time constants when compared to those of pure nematics.
Optical bistability using nematic liquid crystals and polymer-dispersed liquid crystals
Author(s):
Doina Manaila-Maximean;
Constantin Rosu;
Rodica Bena;
Alexandru I. Albu;
Ion M. Popescu
Show Abstract
We present the experimental results concerning hybrid optical bistable devices without resonant cavity using as electro-optic modulators a nematic liquid crystal cell and a polymer dispersed liquid crystal film. Bistable operation was studied for different control voltages and multistable behavior was studied for the polymer dispersed liquid crystal film as a function of the control voltage frequency.
IR absorption of TiO2 thin films
Author(s):
Marius D. Stamate;
G. I. Rusu;
Ioan Vascan
Show Abstract
The titanium oxide films were deposited on glass by reactive sputtering system, in different oxygen partial pressure. In this paper we present the IR absorption of TiOx thin films, deposited through a d.c. circular magnetron system. We found several common peaks of absorption located around 500 cm-1, 530 cm-1, 582 cm-1, 638 cm-1 and 800 cm-1 that are corresponding to Ti- Ox links energy.
Computerized lateral-shear interferometer
Author(s):
Sorin A. Hasegan;
Angela Jianu;
Valentin I. Vlad
Show Abstract
A lateral-shear interferometer, coupled with a computer for laser wavefront analysis, is described. A CCD camera is used to transfer the fringe images through a frame-grabber into a PC. 3D phase maps are obtained by fringe pattern processing using a new algorithm for direct spatial reconstruction of the optical phase. The program describes phase maps by Zernike polynomials yielding an analytical description of the wavefront aberration. A compact lateral-shear interferometer has been built using a laser diode as light source, a CCD camera and a rechargeable battery supply, which allows measurements in-situ, if necessary.
Amorphous Se/CdSe and SiOx/CdSe multilayers
Author(s):
Mihai A. Popescu;
F. Sava;
A. Lorinczi;
Elena Vateva;
D. Nesheva;
G. Tchaushev;
Ion N. Mihailescu;
P.-J. Koch;
S. Obst;
H. Bradaczek
Show Abstract
Amorphous multilayers based on Se and CdSe alternated sublayers were successfully prepared by thermal vacuum evaporation and laser ablation with the periodicity of 22 nm. The multilayer structure is stable up to approximately 70 degree(s)C. In the samples prepared by laser ablation a large contraction of the multilayer stacking occurs by annealing. Amorphous SiOx/CdSe multilayers with the periodicity of approximately 15 nm were successfully prepared by thermal vacuum evaporation. The structure is stable up to 400 degree(s)C annealing temperature. Pulse excimer laser irradiation of the SiOx based multilayer produces an expansion of the interlayer distance with approximately 0.33%.
Aluminophosphate glass with CdSxSe1-x microcrystallite for optoelectronics
Author(s):
Rodica Rogojan;
Mihai Elisa;
Paul E. Sterian
Show Abstract
Until now, all studies were done over the semiconductor glasses doped with CdSxSe1-x, in which the microcrystallite phase was grown into a vitreous silica matrix. Our study was made as for growing microcrystallites of CdSxSe1-x into a vitreous aluminophosphate matrix. In the first step, the samples of semiconductor glass were obtained by melting the raw materials batch and then by adding sulphur selenium and cadmium into the molten glass. In the second step, the resulted glass was annealed in order to bring about the microcrystallite nucleation and growing process. Both linear and non-linear optical properties are deeply influence by the microcrystallite size, which, on its turn is determined by the duration and temperature of the annealing treatment. By means of a spectrophotometer (SPECORD M- 42), were drawn absorption, transmission and fluorescence spectra, in visible domain. From the shape and the absorption edge of these spectra, we are able to characterize the microcrystallite growing process. From these spectra it can be observed a shift of the absorption edge to red which depends on the microcrystallite size.
New principle for self-calibration techniques in phase-shift interferometry
Author(s):
Adrian Dobroiu;
Dan Apostol;
Victor S. Damian;
Victor Nascov
Show Abstract
A new self-calibration principle for phase shift interferometry is introduced, involving a whole-field consideration of the information contained by the interferograms. The principle is illustrated for the three-sample case, which was previously known as not having a self-calibration capability. Three related self- calibrating algorithms for phase shift interferometry are proposed, all of them based on this principle. The input of the algorithms is the set of three interferograms, and the output consists in both the correct phase shifts and the phase map of the wavefront being analyzed. No information on the actual phase shifts has to be supplied.
Instruments and standard measurement procedures for laser beam characterization
Author(s):
Ruediger Maestle;
C. Schmitz;
F. Varnik;
Adolf Giesen;
Helmut Huegel
Show Abstract
The EUREKA-project CHOCLAB (Characterization of Optical Components and Laser Beams), which was initiated in 1995, aims to investigate and develop instruments and standard measurement procedures for laser beam and laser optics characterization. From the start of the project, one of the main work items in the field of laser beam characterization has been the determination of the beam propagation parameters (beam width, divergence angle and beam propagation factor). The most common measurement devices for these purposes are 2d-matrix-cameras (i.e. CCD-cameras), 1d or 2d scanning devices (i.e. scanning pinholes and/or moving knife- edges)--both of them requiring further evaluation of the measured power density distribution to obtain laser beam parameters--and variable transmission/reflectivity optical elements, which allow the direct measurement of beam properties. The advantages and drawbacks of the different types of measurement devices, as well as measures to reduce systematical and statistical errors will be discussed.
Laser frequency comparisons involving Romanian length standard and traceability
Author(s):
Gheorghe Popescu;
Jean-Marie Chartier;
Fabrizio Bertinetto;
Frantisek Petru
Show Abstract
We present final results from four laser frequency comparisons involving the following He-Ne/Iodine lasers operating at wavelength (lambda) equals 633 nm: the laser RO.2 from the National Institute for Physics of Lasers, Plasma and Radiation (Romania); the laser BIPM4 from the Bureau International des Poids et Mesures (France); the laser IMGC4/5 from the Institute for Metrology `Gustavo Collonetti' (Italy); the laser INVAR3 from the Institute for Scientific Instruments (Czech Republic); the laser NMS121 from the National Standards Laboratory (Norway). We report the results coming from matrix determinations on the lines d, e, f, g and then, by reducing all mean frequency differences to the same reference laser (BIPM4), we presented them as frequency traceability of a laser through that of the reference laser.
All-direction localizer of pulsed optical sources
Author(s):
Petre P. Digulescu;
Paul E. Sterian
Show Abstract
There are many applications in which the direction to some pulsed optical sources have to be determined: pointing and tracking systems for laser based free-beam optical communications, laser writing systems, ECM and so on. A mathematical model of a localizer system intended for a laser warning system is developed based on the amplitude monopulse method. A linear transducer of the pulse energy into the time interval was used. The block diagram was designed and implemented based on general purpose devices and integrated circuits. The numerical results of the software simulation are presented. The system may be implemented using ASIC techniques and consequently it's performance, especially the angular precision, can increase.
UV radiation sensors with unitary and binary superficial barrier
Author(s):
Valerian Dorogan;
Tatiana Vieru;
V. Kosyak;
I. Damaskin;
F. Chirita
Show Abstract
UV radiation sensors with unitary and binary superficial barrier, made on the basis of GaP - SnO2 and GaAs - AlGaAs - SnO2 heterostructures, are presented in the paper. Technological and constructive factors, which permit to realize a high conversion efficiency and to exclude the influence of visible spectrum upon the photoanswer, are analyzed. It was established that the presence of an isotypical superficial potential barrier permits to suppress the photoanswer component formed by absorption of visible and infrared radiation in semiconductor structure bulk.
New type of sensor of radiation in a wide range of energy
Author(s):
Andrei M. Andriesh;
Sergei A. Malkov;
Victor I. Verlan;
M. G. Bulgaru
Show Abstract
The Me-Amorphous chalcogenide semiconductor (AChS)--dielectric- semiconductor (Me - As2Se3: Sn - SiO2 - Si) (MChDS) structure was obtained. There have been found that under the lighting in electric field the MChDS in dependence from applied external direction of electric field positive or negative are charged. There were found that quantity of accumulated charge from light intensity have been depended linear type Q equals Qmax ((alpha) + (beta) D), where D--is the dose of radiation (D equals I t, where I is the intensity and t duration of radiation). There were studied and developed three different type of signal recording: by measuring of the photoempf, displacement photocurrent and accumulated charge, which allow to propose two type of sensors of radiation. The dose measuring and the image writing and readout processes in the real time and accumulation of the small signals regimes. The space functional separation of the recording and readout allows to carry out understroing repetition readout of the image and other operations.
Interference devices for noncontact diagnostics of arbitrarily shaped rough surfaces
Author(s):
Peter P. Maksimyak
Show Abstract
The relationship between statistical structure parameters of rough surface and associated correlation parameters of scattered field is used to develop a method for rough surface diagnostics. The treatment is based on the model of random phase object with inhomogeneity phase dispersion (sigma) 2qq(0) < 1. The proposed diagnostic methods are applicable to surfaces with roughness period comparable to the radiation wavelength employed, low-reflectance and arbitrarily shaped surfaces, and surfaces of a thin plane-parallel plate. The sensitivity limit of the methods in measuring the standard deviation of surface profile from base line is about 0.003 mm.
Optical studies on sedimentation of suspensions
Author(s):
Sorin Anghel;
Iancu Iova;
Stefan Levai;
Ion Iorga-Siman;
I. Iosub
Show Abstract
Sedimentation of the suspension process is important, especially in pollution, biologic liquids or polymers studies. Unlike the usual methods, as those using pipettes, areometer or balances, the optical ones are nondestructive and more accurate. During sedimentation produced by the braked fall of the solid particles in suspension, fluctuations produced by an opposite vertical diffusion occur; this process is lost using the chemical methods, which weight the mass fallen on a submersed plate. We used a scattering method, based on the attenuation of a laser beam which, in the absence of absorption, describes the variation of solid particles' concentration in the suspension.
Quadrant detector based on InGaAsP heterostructures
Author(s):
Valerian Dorogan;
Vladimir I. Brynzari;
Tatiana Vieru;
V. Kosyak
Show Abstract
A new device called selective quadrant-detector, realized on the basis of InGaAsP heterostructures, is presented in the paper. It consists of a circular photodiode-quadrant with protective peripheric ring, having selective sensibility optimized for (lambda) equals 1.06 micrometers , in the center of which a photodetector integrated in the same crystal is formed. The photodetector has own capacity C equals 1 - 5 pF and can be used for receiving the high frequency (f > 1 GHz) optic signals and the small duration (t <EQ 1 ns) unitary signals. The presence of central photodetector decreases the coordinate characteristic abruptness (K equals 8(DOT)103 V(DOT)W-1(DOT)mm-1(and photocurrent intensity with 8 - 10%. Absolute spectral sensibility is S(lambda equals1.06) equals 0.57 A/W and photosensibility spectrum semiwidth is (Delta) (lambda) <EQ 100 nm.
Photothermal method using a pyroelectric sensor for thermophysical characterization of agricultural and biological samples
Author(s):
A. Frandas;
Dorin Dadarlat;
Mihai Chirtoc;
Henk Jalink;
Dane D. Bicanic;
D. Paris;
Jean S. Antoniow;
Michel Egee;
Costica Ungureanu
Show Abstract
The photopyroelectric method in different experimental configurations was used for thermophysical characterization of agricultural and biological samples. The study appears important due to the relation of thermal parameters to the quality of foodstuffs (connected to their preservation, storage and adulteration), migration profiles in biodegradable packages, and the mechanism of desiccation tolerance of seeds. Results are presented on the thermal parameters measurement and their dependence on temperature and water content for samples such as: honey, starch, seeds.
Techniques for accurately measuring laser beam width with commercial CCD cameras
Author(s):
Carlos B. Roundy
Show Abstract
CCD cameras are very useful instruments for the measurement of laser beam profiles and beam width. A principal advantage of CCD cameras is that they measure the entire beam cross-section simultaneously. However, camera noise and baseline offset can create significant errors in beam width measurements if not processed properly. Techniques have been developed that effectively compensate for both problems and enable very accurate measurements. These techniques are described, along with examples of the measurement accuracy under varying conditions. Additional signal processing is described that further enhances the ability to make accurate measurements.
Definition of a robust measurement of similarity for the localization of small shapes in scenes
Author(s):
Xavier Fernandez;
Josep Ferre-Borrull;
Salvador Bosch
Show Abstract
After analyzing the problems related to finding a small shape in a scene, we introduce a nonparametric similarity measure based on the Kolmogorov-Smirnov statistic, which proves to be robust for template-matching problems where a target of binary characteristics is to be located inside a gray-scale image. We show that the Kolmogorov-Smirnov statistic gives the optimum thresholding level for the image and may be computed without actual thresholding of the image. Some interesting properties of the proposed similarity measure are exposed and compared to the corresponding properties of normalized correlation.
Light scattering in liquid crystals
Author(s):
Marcela Ursache;
Margareta Socaciu;
Cristian Sarpe-Tudoran
Show Abstract
In this paper we study the light scattering on the different mesophases of TBBA-CM mixture. We used He-Ne laser radiation and we derived a simple theoretical model of the diffusion process. The results are in good agreement with the data provided by other experimental methods.
Digital laser powermeter
Author(s):
Emil Smeu;
Niculae N. Puscas;
Ion M. Popescu
Show Abstract
A digital powermeter was developed for measuring the power of laser beams using an electrically calibrated thermopile. This choice allows metrological quality measurements in a broad spectral range and an accurate calibration, but the electronic readout must meet some severe specifications concerning internal fluctuation (generally, most of commercially available radiometers, even advanced, do not). The reported powermeter has very low internal fluctuation (both drift and noise, in respect with its resolution). Original, yet simple circuitry was developed for low noise and for an accurate zero setting (even with a high background). The most important of these internal circuits is described. Statistical noise tests are also presented and some comparisons with advanced commercial powermeters. A large number of tests, each of them containing 500 - 900 measurements (values), revealed for the reported powermeter that `0' reading is the most probable noise value (i.e. the most often found), its probability being in all cases larger than 99% on the most sensitive range and equal to 100% on all other ranges.
Structured light in visual inspection
Author(s):
Constantin Blanaru;
Virgil V. Vasiliu
Show Abstract
When a processed part is visually inspected along a projected line of several meters in length, generated by adequate cylindrical optics, the gaussian beam intensity profile along line length will create problems given by the fading edges of the intensity profile, the variation of the light level across the line and the presence of `hotspot' in the center of the line. In order to avoid these problems, we used the structured light generated by a special developed laser diode producing a non- gaussian (evenly illuminated) distinct line. The visibility of the projected line in real working conditions, depth of field and focusing performances of the beam are presented, as they have been evaluated.
Romanian primary length standards involved in international comparisons
Author(s):
Gheorghe Popescu
Show Abstract
One of the three methods specified for the practical realization of the meter uses molecular transitions. He-Ne lasers operating at 633 nm wavelength and frequency stabilized by saturated absorption in 127I2 were built at the National Institute for Lasers, Plasma and Radiation Physics, Laser Department and their performances tested in international comparisons during last four years at the Bureau International des Poids et Mesures (BIPM. 1993, 1995), at the Institute for Metrology `Gustavo Collonetti' (IMGC, 1994) and at the Institute for Scientific Instruments (ISI, 1996). Comparative results regarding frequency difference, repeatability and stability are presented. Results proved a good reproducibility of the performances during the time.
Calibration procedures for a 10.6-um laser calorimeter
Author(s):
Michael Kennedy;
Detlev Ristau;
Gabriel Dumitru;
Dan G. Sporea;
Clementina A. Timus
Show Abstract
The paper presents the theoretical background of laser calorimetry as a method to investigate the absorptance of optical components, according to the recently adopted ISO Standard 11 551. An experimental set-up for optical absorption measurements, including a cw CO2 laser and a calorimetric chamber, is presented. The calibration of the laser calorimetric set-up is also described. The calibration involved several steps: laser power calibration, evaluation of chamber sensitivity, electrical calibration using electrically heated samples and optical calibration utilizing 100% absorptance samples. There were measured the conversion factors for the laser power and for the sample temperature; there were calculated over-all correction factors for the different substrates and they could be placed within +/- 4% around their mean value.
Estimation of some physical characteristics of metallic powders using VIS reflectance measurements
Author(s):
Marius Nicola;
Eugen Darvasi;
Despina Gomoiescu;
Emil A. Cordos
Show Abstract
The effect of the composition and of the grain size of Fe, Cu and Sn metallic powders on the reflectance spectra in VIS range have been studied. Calibration curves for determination of the percentage composition of Fe-Cu mixtures and for determination of the medium grain sizes for Fe, Cu and Sn powders were plotted.
Method for small birefringence evaluation
Author(s):
Anca Maria Beldiceanu
Show Abstract
A simple experimental method for evaluating small birefringences is reported. This method is based on the amplification of low phase retardation values using a rotary (lambda) plate in conjunction with the birefringent sample. The new value of retardation is readily evaluated in white light with the sensitive (lambda) plate or is measured with a system of a compensating plate and wedge in monochromatic light. The initial small retardation is determined by interpolation from theoretical curves. This unexpensive method can be applied in any biological, chemical or mineralogical laboratory where simple polarizing accessories are available.
Circularity measurement by laser triangulation
Author(s):
Victor S. Damian;
Constantin Blanaru;
Dan Apostol;
Adrian Dobroiu;
Victor Nascov
Show Abstract
The method and experimental results of circularity measurements by optical triangulation are presented. The measuring system is a laser based one, using a bi-cell detector with rectangular active surface shape and diagonal gap. The measured data were fitted with a parametric function depending on the position of the tested object center, relative to the center of the rotating table. A resolution of 2.5 micrometers /mW is reported. This sensitivity is satisfactory for the majority of industrial applications-- circularity measurement and centering.
Polarizing interference coatings made with anisotropic thin films
Author(s):
Francois Flory;
Celine Defay
Show Abstract
It is now well known that the microstructure of materials in thin film form can be slightly different from that of corresponding bulk materials. Conventional evaporation using a heated crucible or an electron beam gun generally leads to a lacunar structure in columns. Some consequences of this microstructure on the optical properties of the films are well-known. The refractive indices are slightly smaller than that of the bulk material; water adsorption-desorption in the voids leads to variations of the spectral reflection and transmission of the coatings. But apart from these disadvantages, the columnar structure can present advantages because it also induces anisotropy of refractive index. When deposited with an ion beam assistance the microstructure of the material is modify and so is its anisotropy. The anisotropy can then be controlled through the ion energy, making it possible to construct multilayer filters combining both isotropic films and anisotropic films. This opens the way for the making of components acting on the polarization state of light. Results of calculation for different components are presented. Planar non absorbing monochromatic polarizers or polarization rotators can be made in this way. The difficulty in controlling the deposition comes from the fact that the anisotropic layers must be deposited on non rotating substrates. This problem is discussed and examples of measured optical properties of multilayer filters will be given.
Special mirrors for cw CO2 high-power lasers
Author(s):
Victor Rares Medianu;
Iulian Gutu;
Geo Georgescu;
Mihail F. Lazarescu
Show Abstract
`Special mirror' concept is presented as a `spare module' for a GaAs extracting mirror technological processed with GaAs thin films, mounted within two kinds of c.w. CO2 laser resonators: U-type resonator (with optical pathlength Lr equals 4 m) and U- type folded resonator with V-discharge on each branch, reversal mirror provided (with the optical pathlength Lr equals 8 m), experimentally used to obtain good quality laser beam. The extracting mirror presents variable reflectivity, acting as a super-Gaussian mirror and working as an output coupler in the resonator, providing total compensation of the refractive index and of the small gain asymmetries.
Spectrophotometry, ellipsometry, and computer simulation in thin film developments
Author(s):
Salvador Bosch
Show Abstract
Thin film deposition techniques are widely used in industry because of the variety of practical applications where they may be appropriate. The manufacture of thin film coatings normally requires high vacuum equipment, with additional attachments such as electron beam evaporators, ion guns, quartz oscillator microbalance, etc. Besides the technological problems involved in the deposition of the films, the optical characterization of the coatings obtained is a major issue. For example, for wideband antireflection coating of lenses a precise control of the refractive indices and thicknesses obtained is required, together with a good uniformity inside the whole vacuum chamber. Thus, techniques for the measurement of refractive indices and thicknesses of thin films have to be available in laboratories related to the deposition plants. Several characterization apparatus are quite standard in industry, because their wide range of applications and relative low cost (spectrophotometer is the typical example). Other apparatus are much more specific and much more expensive like ellipsometers, secondary ion mass spectrometers, transmission electron microscopes--, although monochromatic ellipsometers may sometimes be accessible because of its moderate cost. Finally, very powerful desk computers are really cheap nowadays, so computation facilities are always available at any laboratory. The aim of the present work is to illustrate the combined use of three basic laboratory techniques- -spectrophotometry, monochromatic ellipsometry and computer simulation--in the development of thin film coatings and filters.
Structure investigations of optical coatings on GaAs substrate
Author(s):
Clementina A. Timus;
Victor Rares Medianu;
Rares V. Medianu;
Geo Georgescu;
Eugen Vasile
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ZnS, BaF2 and GaAs thin films on NaCl and GaAs substrates, produced by thermal evaporation and r.f. magnetron sputtering as antireflective and reflective coatings for 10.6 micrometers are investigated. Optical and electronic microscopy (TEM and SEM) with EDAX and SAED had been approached to study the structure and morphology of optical coatings, corroborated with the technological parameters of the deposition. The columnar structure of the thermally evaporated BaF2 film was observed. Uniformity and deposition rate for r.f. magnetron sputtering deposition, without ion assistance turns out to be very critical, since the induced mechanical stresses could compromise the optical film.
Characteristics of a carbon/nickel multilayer structure for soft x-ray optics deposited by rf magnetron sputtering
Author(s):
Magdalena Ulmeanu;
Geo Georgescu;
Rares V. Medianu;
Nicoleta Nastase;
Cornel Ghica;
Virgil V. Vasiliu
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In order to make X-ray-UV interference mirrors, we tried to obtain a periodic multilayer structure with thin films of two materials, a high absorption material (Ni) and a low absorption material (C) on a quartz substrate. We present theoretical approaches to determine the optimum values of the thicknesses of each thin film and the number of periods required for maximum reflectivity at normal incidence of a soft X-ray mirror working at (lambda) equals 50 angstroms. We also describe the experimental procedures used for obtaining the multilayer structure and the microscopically investigations.
New method for automatic optimization of glass combination in optical systems working in the visible range
Author(s):
Daniel Ralea;
Raluca-Maria Marginean;
Marinica Marzu
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The algorithm presented in this paper proposes a way to find the optimum glasses that assure a better correction for optical apparatus with the human eye as a final receiver. The model (Ne, v1, v2), based on the Buchdahl formula, gives an approximation error for the refraction index less than 5(DOT)10-5 for visible domain. We introduced in the merit function used for optimizing the optical system an operand that describes the existence of an optical glass. This operand was defined so that the obtained value for Ne, v1 and v2 can be closed to some values for a real glass. A definition for this operand is obtained using the PNe, Pv1, Pv2, probabilities of existence for a glass with a certain parameter Ne, v1 or v2. Another possibility to define this operand is to describe the volume occupied by the optical glass in (Ne, v1, v2) space with some elliptical functions. The probabilities and the elliptical functions were found after an analysis for all optical glasses listed in the Schott catalogues was made.
Ray tracing for ophthalmic optics: specific developments for GRIN materials
Author(s):
J. R. de F. Moneo;
Ignacio Prades Juvells;
Santiago Vallmitjana;
Salvador Bosch;
Arturo Carnicer;
Ignasi Juan I. Labastida;
Julio Perez-Tudela
Show Abstract
In this work we present the developments for the simulation of image formation through an ophthalmic lens. The procedure is, essentially an exact ray tracing taking into account the particular mobility conditions of the exit pupil. This leads to the computation of astigmatism as a function of the field angle considered. In the computer program, the use of a commercial glass with a gradient in the refractive index (GRIN material) is foreseen. This latter feature proves to be useful for two practical objectives: modifying the power and the astigmatism of the lens. To illustrate these points, an example based on a lens made by deforming a plane parallel plate of GRIN material will be presented.
Solutions of single-layer synthesis with symmetrical three-layer periods
Author(s):
Andreea Trache;
Paul T. Miclea;
Voicu Lupei;
Mihai P. Dinca
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Admittance matching is generally used in the design of optical components which require in the same time high reflectance and high transmission bands. The matching is done at the both sides of the basic stack by synthesizing an equivalent layer with symmetrical three layer periods. In order to obtain a broad transmission band, a quasi-matching is necessary around the matching wavelength. The paper studies the solutions provided by analytical synthesis of the matching stack for a number of one to three periods.
Yield optimization of multilayer optical coating by modeling of the monitoring process
Author(s):
G. L. Muscalu
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In this paper, one investigated the yield of some optical coatings with a nonquarterwave structure within the classical vacuum systems by modeling of the monitoring process. The correlation of the synthesis and modeling process, allows to set the optimum monitoring process for different types of coatings. The experimental results tested on antireflection coatings are according to the theoretical ones.
Interferential filter design with continuously variable refractive index
Author(s):
Andreea Trache;
Voicu Lupei;
Mihai P. Dinca
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The paper briefly presents an original method for design of inhomogeneous thin films which takes into consideration from the beginning the finite character of the optical thickness. At the beginning, the best solution is obtained in terms of the value of a complex function on a certain spectral grid. At the second step, the design is converted in terms of refractive index profile. Special care is taken to minimize the variations of this profile. Then, a program using this method, written as Windows application, is described together with a design example providing a spectral dependence of the reflectance having the shape of Romanian Athenaeum building.
Filters with induced transmission
Author(s):
Gheorghe Honciuc
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Some problems appeared during the production of induced transmission filters are analyzed in the case of some technological limits. One can reveal the dependence between the performances of induced transmission filters and production technological parameters. The experimental results are compared to those ones characteristic to other types of narrow band interference filters.
Software for optical coating design
Author(s):
Gheorghe Honciuc;
Gh. Singurel
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A Windows 3.1 application is shown for editing, analyzing, optimizing, designing technologies and determining the optical constants out of the (R,T) measurements. A dynamic arborescent structure of data (optical coatings) has been used, allowing a great flexibility in describing the optical coatings. The optical coatings of the arborescent structure are defined on the same thin films (defined in root), the change of a layer being detected by all the optical coatings of the arborescent structure, containing that layer. The layers are seen by coatings by mean of some groups (structures) of layers and some scale factors, the groups being the elements that describe the coating. So, one can study an optical coating or parts of coating (e.g. optical monitoring) under different conditions.
Electrostatically driven dynamic focus system
Author(s):
Horatiu Totia;
Marius Micluta
Show Abstract
Real-time accurate positioning of laser beams and optical images on 3D targets, as well as focus correction in the flat field laser scanning, are provided by dynamic focus systems. Commonly used zooming devices involve rather complex driving mechanisms to control the relative motion of the lens systems. A possible, cost-effective alternative to this approach is to use a lens with variable focal length. The design of a dynamic focus system based on this principle is presented, and a suitable driving method, using electrostatic interactions, is also proposed. Dimensional design formulae are given, together with performance evaluation calculations.
III-V compounds and piezoelectric ceramic thin films deposited by reactive PLD: application to sensor building
Author(s):
Maria Dinescu;
P. Verardi;
F. Craciun;
Catrinel A. Stanciu;
Raluca Dinu;
C. Gerardi;
L. Mirenghi;
Mariuca Gartner;
Viorel Sandu
Show Abstract
High quality AlN, GaN, ZnO and PZT thin films were deposited on different substrates by laser ablation of metallic or PZT targets in nitrogen or oxygen reactive atmosphere. A YAG laser ((lambda) equals 1.06 micrometers , tFWHM equals 10 ns, 0.3 J/pulse) was used as laser source. The target collector distance was varied in the range 3 - 8 cm, the gas pressure in the range 10-3 - 10-1 mbar, the collectors were heated at temperatures between 200 and 400 degree(s)C. The influence of the process parameters on the physical properties of the deposited films was analyzed. The profile of atoms inside the film was evidenced by SIMS analysis. Depth profile XPS and AES confirm the presence of Al-N, Ga-N and Zn-O bonds inside the films. X-ray diffraction studies revealed different crystalline orientation depending on deposition conditions. The recorded spectra show the crystalline orientation of the layers, at collector's temperatures lower than the best results reported in literature. Optical absorption spectroscopy studies in the UV and visible range evidenced a high transparency (over 80% transmission) for the AlN, GaN and ZnO deposited films. For PZT a particular result consists in the piezoelectricity of the deposited films `as received', without any subsequent thermal or electric treatment.
Laser monitoring of pesticides in water
Author(s):
Mihail-Lucian Pascu;
N. Moise;
Letitia Voicu;
T. Negoita;
G. Manolescu;
Adriana-Loredana A. Smarandache
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Pesticides monitoring at low concentrations using optical absorption, laser induced fluorescence (LIF), fluorescence lifetime measurements and gas chromatography are reported. The studied pesticides were chlortriasines (athrasine, propasine and simasine) and organophosphoric pesticides (dichlorvos and parathion). Since in normal conditions the chlortriasines show absorption spectra in ultraviolet (around 250 nm), to obtain fluorescence spectra in the visible they were treated with pyridine and ethyl ester of cyanoacetic acid in basic medium. The LIF spectra of chlortriasines are measured at concentrations of pollutants between 5 ppm and 20 ppm. The molecular complex fluorescence spectrum induced by pulsed laser radiation at 545 nm, available from a tunable dye laser, exhibited a maximum of 577 nm; it remained unchanged for three hours, following which the intensity decreases as a consequence of the complex destruction (decomposition). The fluorescence lifetime of the molecular complex measured using a fast photodetector was 2.6 ns, immediately after complex formation. The organophosphoric pesticides were monitored using a rather different initial chemical treatment, at the end of which a quinino-vanado- molibdophosphoric complex (PMo10V2O39)2(C20H24O2N2H2)3 was formed. The fluorescence spectra of these pesticides induced by pulsed laser radiation at 337.1 nm available from a pulsed nitrogen laser (700 ps pulse time width, 300 (mu) J/pulse energy) exhibited a maximum at 445 nm with a FWHM of 80 nm. The low concentration detection limits were 0.2 ppm for P in dichlorvos (dichlorvos concentration 14.18 ppm) and 0.2 ppm for P in parathion (parathion concentration 17.8 ppm). These methods in correlation with optical absorption, classical fluorescence and gas chromatography methods were applied to monitor pesticides in water samples collected from the North Pole zone following two expeditions dated March-April 1995 to Severenaia Zemlia Archipelago and July-August 1996 to Spitzbergen Archipelago. Comments about the monitoring of pesticides content of these samples are made.
Detection of atmospheric pollutants by pulsed photoacoustic spectroscopy
Author(s):
Miruna Roman;
Mihail-Lucian Pascu;
Angela Staicu
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Pulsed laser photoacoustic detection of NO2 and SO2 is reported. The laser source is a pulsed molecular nitrogen laser emitting at 337.1 nm. The average energy per pulse is about 350 (mu) J and the pulse duration 10 nsec. For detection we used a piezoelectric transducer (TUSIM-N.I.M.P., resonance frequency 4 MHz) and an electret condenser microphone (Trevi EM 27). The photoacoustic cell was a nonresonant one, with a cylindrical shape. The laser beam was centered along the cylinder axis. Linear dependence of the photoacoustic signal on pollutant pressure was obtained. This linearity is in a good agreement with theoretical considerations. The photoacoustic signal was measured for pollutants pressure between 1 torr and 100 torr for NO2 and between 35 torr and 100 torr for SO2.
Modeling of atmospheric effects on the angular reflectance characteristics of vegetation canopies
Author(s):
Gheorghe Stancalie
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The capabilities of off-nadir satellite observing directional variations in terrestrial surface reflectance, not yet sufficiently present in operational satellite series, are expected to be developed in the near future. The main objective of the paper is to study and modeling the atmospheric effects on the typical angular reflectance characteristics of vegetation surfaces in the visible and near-infrared regions. For the evaluation of the atmospheric contribution to the satellite data, radiative transfer model simulations, with ground radiometric measurements have been performed. The paper discusses the signatures that the atmosphere imposes on the angular distribution of the emerging solar radiation above aerosol-loaded atmosphere. The model calculations have also showed that some atmospheric-invariant features of the angular reflectance distribution, like the aerosol forward scattering peak or the hot spot in the antisolar direction, may be used as discriminant surface reflectance characteristics in the case of low aerosol- loaded atmosphere.
