This PDF file contains the front matter associated with SPIE Proceedings Volume 7027, including the Title Page, Copyright information, Table of Contents, Introduction, and the Conference Committee listing.

Materials processing by ultrafast lasers offers several attractive possibilities for micro/nano fabrication applications. Several exciting prospects arise in the context of surface and bulk laser induced modifications. These form the basis for diverse applications, including the development and functionalization of laser engineered surfaces, the laser transfer of biomolecules and the functionalization of 3D structures constructed by multiphoton stereolithography. In particular, two examples will be discussed in the following, namely a new approach for the development of superhydrophobic, self cleaning surfaces and the fabrication of functionalized scaffolds, for tissue engineering applications.

This paper describes two topics. (1): Nano-processing by near-field optics can fabricate nano-scale structures even with near-infrared 800 nmTi:saphire laser. New phenomena using particles, leading to a new nano-processing technique via plasmonics, even with the use of dielectric particles is reported. The physics of nano-hole fabrication process is switchable simply by the laser fluence. (2): ZnO nanorod arrays on Si (100) substrate were grown by pulsed laser deposition (PLD) method, and then coated with Au. Two samples of Au-coated nanorod arrays with different average diameters of 150 nm and 400 nm were prepared to investigate the size dependence of the surface enhanced Raman scattering (SERS). The diameter of the nanorods was well controllable by the substrate position during PLD. High SERS enhancement was observed from both Au-coated ZnO nanorod arrays. The Raman spectra of Rhodamine 6G (R6G) as low as 1 nM were measured with average diameter of 400 nm at an excitation wavelength of 532 nm.

This paper reviews our and our colleagues' recent results concerning planar waveguide lasers in KY(WO₄)₂:Yb³⁺ near 1 μm and channel waveguide lasers in α-Al₂O₃:Ti³⁺ near 800 nm.

Temperature fields in low carbon rimming steel with 2.5 and 0.45 mm thickness during surface treatment with pulsed Nd:Glass laser have been simulated. Two models namely analytical and finite elements method (FEM) have been applied for solving the one dimensional differential heat transfer equation. The analytical model is assuming constant thermophysical properties, semi-infinite size of the treated material and no heat transfer with ambient atmosphere. For the FEM the influence of the thermal dependence of the thermophysical properties and the finite size of the treated material has been investigated. It has been shown that the one-dimensional analytical model could be successfully used for the estimation of the temperature on the surface of both the thicker and the thinner steels, but is not suitable for the characterization of the thermal field in the depth of the thinner material. The oxidation kinetics during laser treatment has been simulated and the influence of the formed oxide film on the coefficient of absorption and thus on the temperature field has been analyzed. For this purpose two models, namely the "smooth surface" and the "rough surface" model have been applied. It has been found that the kinetics of the oxide film growth is defined only by the rate of the oxygen supply to the treated surface and within the laser pulse duration (7ms) is linear in time. According to the "smooth surface" model the consideration of the surface oxidation increases the optical absorption coefficient from 0.4 to 0.9 while according to the "rough surface" model this increase is up to 1.0. The absorption coefficient increase is accompanied with the same ratio increase of the temperature in respect to that when the oxidation has not been taken into account.

Sputtering of Cu/Ti layers was performed by Ar⁺ions. Analysis of the atomic and molecular composition of the sputtered plume was performed by means of Ultra-short Laser Neutral Mass Spectrometry (US-LSNMS) and Secondary Ion Mass Spectrometry (SIMS). Several ionic masses were observed and systematically studied with respect to the exposure time, laser fluence and target composition. The obtained data for complex layers indicate generally a good agreement between SNMS and SIMS. SIMS is more sensitive for many elements however the mass interferences can limit the analytical applicability. US-LSNMS mass spectra of Cu(Ti) sample have been acquired for different exposure times. In order to determine the effect of different laser ionization energies over the mass distribution of the elements, mass spectra of Cu(Ti) multilayers at several laser ionization energies were acquired. The elements interdiffusion was analyzed also by US-LSNMS, demonstrating the sensitivity, the limits and the future potential of the SNMS method for material characterization.

Laser cleaning tests were performed on ancient (Roman and Byzantine) coins, which belong to the collection of the Numismatic Museum of Athens, Greece. Coins with various types of surface corrosion were studied, using Q-switched Nd:YAG, CO₂ and Er:YAG lasers and a range of laser pulsing parameters on dry and wet surfaces. A section of each object was cleaned mechanically, by the conservators of the museum in order to show the results of this method. It was discovered that the results of laser cleaning was influenced by the type of corrosion of the surface of the coins. X-ray fluorescence was applied as analytical technique. The results show that XRF could provide detail information about the surface chemical nature of the treated objects, as well as about their past and present state and it leaded to recommendations for restoration with the appropriate laser cleaning conditions.

The photon drag effect has been observed in several semiconductors. It arises from the transfer of momentum from laser radiation to mobile electrons or holes in the material. The sign and the magnitude of the effect depend on the combination of optical, transport and band structure properties of the semiconductor as well as the magnitude of the radiation momentum. The optical rectification is a second order phenomenon arising from the generation of polarization in a non-linear medium at the passage of an intense optical beam. Both effects are generally referred as radiation pressure effects. The intention of this work is to present and discuss new experimental evidence of photon drag-effect in diamond structure and photon drag-optical rectification in III-V semiconductors using Er:YAG laser emitting at 2.94 μm, CO₂ laser emitting at 10.6 μm and at 9.6 μm, Nd:YAG laser emitting at 1.06 μm, Er:Tm:Ho:YLF laser emitting at 2.06 μm and Cr:Tm:Ho:YAG laser emitting at 2.08 μm. No saturation effects were found indicating that detectors based on these effects can be used as recording devices of pulses down to 0.1 ns. Measurements have been made on the response of the photon drag and the optical rectification detectors of Ge, Si, GaAs, GaP of several orientations. The responsivity results are converted, using the relevant theoretical equations, in to S, P and D coefficients. The experimentally obtained results are theoretically explained and are compared with previous results of other wavelengths in the literature.

The formation of nanoparticles at ultrashort laser ablation of gold in vacuum is investigated theoretically. The analyses of the nanoparticle formation mechanisms and their initial evolution are performed on the basis of molecular dynamics (MD) simulation. The study is carried out for Au target irradiated by laser pulses of 100 fs duration at laser wavelengths of 800 nm. The evolution of the ablation process is monitored for time interval of few hundreds of picoseconds. The size distribution of the nanoparticles and their velocity distribution are obtained as a function of the laser fluence. The results indicate that the nanoparticles are formed in the stage of superheated material decomposition and phase explosion and fragmentation are the main mechanisms leading to their formation. The results for velocity and size distributions are compared to the available experimental ones and good agreement is observed.

ZnO thin film growth and ZnO nanorods growth on a Si (100) substrate through a two-step, off-axis pulsed laser deposition (PLD) are reported. ZnO morphologies were measured and the post-annealed ZnO films grown at T_g = 700 °C had very smooth surfaces and the rms roughness was about 0.5 nm. Finally, ZnO post-annealed buffer layer was inserted between ZnO epi-layer and GaN/sapphire substrates. It was confirmed by cathode luminescence (CL) spectrum that the ZnO film grown at 700 °C had very low visible luminescence, which means a decrease of the deep level defects. In the case of ZnO nanorods, controlling growth parameters during deposition enabled to adjust the dimensions of nanorods. The diameters of the grown nanorods ranged from 50 to 700 nm and the lengths are from 2 to 10 μm. The CL spectra were used to evaluate the states of defects within the ZnO nanorods. According to the CL results, the thinnest nanorod arrays were found to have fewer defects, while more defects were inserted as nanorods became thicker.

The slow-light effect, which implies reduction of the group velocity of light by many orders of magnitude, is considered to be one of the most exciting discoveries in quantum optics of the last decade. The physics underlying the effect is related to an extremely steep dispersion of the medium in a very narrow region of its transparency, while all the manifestations of the effect are usually reduced just to a small pulse delay. Perhaps this is the reason why, after the discovery of the slow-light effect, some of the simplest nonlinear phenomena associated with a retarded optical response have been implicitly revised and assigned to reduction of the light group velocity. In this lecture, a few examples of common inconsistencies in the area of the slow-light physics will be presented.

The apparatus for the production and trapping of francium is described and its performances are reported. Latest results on magneto-optical trapping of Francium are summarized: trapping of 209, 210, 211 Francium isotopes, measurements of their trapping frequencies, measurements of diffusion parameters of Francium ions in yttrium. Future experiments on fundamental physics are presented.

We calculated line-shapes of the coherent population trapping (CPT) for the open transition in ⁸⁷Rb by solving time-dependent optical Bloch equations and averaging results for the total excited state populations over atomic trajectories and velocities, while taking into account incident angles to the laser beam. Comparison with experiment produces good agreement for the laser intensity dependence of the CPT line-widths when the laser transverse beam profile is Gaussian. This theoretical model was used to calculate the probe laser CPT in the case of spatially separated pump beam. The probe beam is placed inside the cylindrically-shaped pump beam. The calculations as well as measurements show narrowing of the Hanle resonance due to Ramsey effect.

Sub-Doppler nature of atomic spectra in alkali metal vapor cells of nanometric thickness L (nanocells) allows one to study peculiarities of magneto-optical processes, which occur in a magnetic field for the case when L is of the order of λ (λ is a laser resonant wavelength). We particularly address the issues of practical implementation of the studied processes. The following results are presented. i) A "λ-Zeeman technique" exploiting velocity-selective optical pumping resonances in L = λ Rb cell placed in a B-field, which allows direct determination frequency shifts and modification of transition probabilities of individual Zeeman transitions in magnetic field and is applicable for development of wide-range (~ 0.1 - 1000 mT) optical magnetometers and tunable frequency reference. ii) A technique for locking the laser radiation frequency, B-field-tunable in ~ 500 MHz range, which is based on selective reflection of a circularly-polarized laser beam from Rb vapor cell with thickness L ≈ λ/2.

Coherent Population Trapping (CPT) resonance obtained with linearly polarized laser beam through magnetic field sweep (Hanle configuration) was investigated in ⁸⁷Rb D₁ line. Influence of the coherence due to high-rank polarization moment (hexadecapole moment), created in the medium, on the CPT resonance shape was calculated and experimentally detected in fluorescence. It was observed as an inverted structure at a high power of excitation. To distinguish resonances due to coherence between Zeeman sub-levels with Δm_F=2 from that with Δm_F=4, the Larmour frequency ω_Lmodulated by applying an a.c. magnetic field (a.c. MF). Resonance signal at frequency corresponding to 4ω_L observed in a fluorescence, and after lock-in on the frequency corresponding to frequency difference between sub-levels Δm_F=4.

A construction of a low-cost wavemeter based on the transmittance of a colored glass filter is presented. The device is tested with a free running 654 nm diode laser and its uncertainty is estimated to be about 1 cm^-1, which originates mainly from the mode structure of the diode laser. Along with wavelength measurements, the device can be used also for analysis of the mode structure of free running diode lasers.

We present two original, all optical techniques, to produce a narrowline laser light, fixed at the frequency of a chosen reference atomic absorption transition. The first type of systems is an essential improvement of our method ^3,4 for laser spectral locking using a control by two frequency scanned, competitive injections with disturbed power ratio by the absorption at the reference line. The new development eliminates the narrowing limiting problem, related with the fixed laser longitudinal mode structure. We have proposed an original new technique for continuously tunable single mode laser operation in combination with synchronously and equal continuous tuning of the modes of the amplifier. By adapting the laser differential rate equations, the system is analyzed theoretically in details and is shown its feasibility. The results are in agreement with previous our experiments. The essential advantage, except simplicity of realization, is that the laser line can be of order of magnitude and more narrowed than the absorption linewidth. The second system is based of the laser amplifier arrangement with a gain knock-down from the competitive frequency scanned pulse, except at the wavelength of the desired absorption reference line. The essential advantages of the last system are that the problem of fixing laser mode presence is naturally avoided. The theoretical modeling and the numerical investigations show the peculiarity and advantages of the system proposed. The developed approaches are of interest for applications in spectroscopy, in DIAL monitoring of the atmospheric pollutants, in isotope separation system and potentially - for creation of simple, all optical, frequency standards for optical communications. Also, the continuously tunable single mode laser (and the combination with the simultaneously tunable amplifier) presents itself the interest for many practical applications in spectroscopy, metrology, and holography. We compare the action and the advantages of the two systems proposed.

A model for description of the shapes of the coherent population trapping (CPT) resonances at different geometries of excitation and observation is developed. The numerical calculations, based on the irreducible tensor operator formalism, take into account the experimental geometry, the velocity distribution of the atoms, the Gaussian distribution of the laser beam intensity and the high rank polarization moments (HRPM). The results for different laser beam diameters, aperture of the detection, position of the photodetector etc. are compared with the experimental data. A method for description of the experimental shapes is proposed.

The dynamics of interaction of laser radiation resonant with the transitions of D₂ line in atomic Cs¹³³ in the presence of an external magnetic field is studied. Populations of levels and dynamics of resonant fluorescence at scanning frequency of the laser radiation with linear and circular polarizations are considered.

We present the first experimental observation of Coherent Population Trapping (CPT) in Potassium, obtained with kHz-frequency modulation of the laser light amplitude. It is performed by acousto-optical amplitude modulation of the radiation from an external cavity diode laser, matching the D₁ line of K. The CPT resonances are detected both through K absorption and fluorescence. The resonances are studied in three kinds of K cells: i) pure-evacuated, ii) polydimethylsiloxane (PDMS)-coated-evacuated and iii) Ne-gas buffered. In all cases CPT-resonance narrowing with cell temperature is observed. In the pure-evacuated cell we registered the lowest contrast and the highest width of the resonance, while in buffered/coated cells a strong enhancement of the CPT resonance contrast up to 15% is observed. This behavior is the opposite to the one exhibited by Cs and Rb. The observed contrast enhancement in K is accompanied by more than two orders of magnitude reduction of the resonance width. The results here presented prove the advantage of using Potassium in CPT-based applications.

Nonlinear magneto-optical rotation (NMOR) of linearly polarized light, resonant to the F_g = 2 → F_e = 1 atomic transition of D1 line of ⁸⁷Rb is investigated experimentally, by applying spatially separated laser fields in the Rb vacuum cell. In our experiment, the probe laser beam propagates through the center of the pump laser beam, which has the shape of a hollow cylinder. We have measured the rotation of the probe laser beam polarization with respect to the incident polarization, as a function of the external magnetic field, parallel to the laser beam propagation. We show substantial narrowing of the resonance if the pump beam, with the same linear polarization, is present. The opposite direction of the probe rotation was obtained when the pump laser beam polarization is orthogonal to the probe laser beam polarization.

Radiative lifetimes of 17 excited states in Zr I, in the energy interval 29000 - 40974 cm^-1, have been investigated using the Time-Resolved Laser-Induced Fluorescence (TR-LIF) method. The levels belong to the 4d²5s5p, 4d³5p and 4d5s²5p electronic configurations were excited in a single - step process from levels belonging to the ground 4p²5s² a ³F or to low-lying 4p²5s² a ³P, a ⁵F terms. For 14 levels, the lifetimes have been measured for the first time. Experimental results are compared with theoretical calculations performed with a multiconfigurational relativistic Hartree-Fock method including core polarization effects.

This work is concerned with the line profiles, amplitudes and widths of the coherent population trapping (CPT) resonances due to low frequency Zeeman coherences, in the Hanle configuration, applied to ⁸⁷Rb atoms in the vacuum cell. Detailed calculations of the fluorescence were done with two different transverse intensity profiles of the excitation laser tuned to the open F_g = 2 → F_e = 1 transition. Comparison with experiment produces good agreement for the laser intensity dependence of CPT line-widths in the wide range of the laser intensity, when the laser transverse beam profile is Gaussian. Results for both step-like and Gaussian profile of the laser beam show asymptotic 1/√d dependence (d is the laser beam diameter) of CPT line-widths, for large range of the laser intensity.

Protection of buildings and critical public infrastructure against blast load has been recently improved by retrofitting glass windows with a safety film. As the exact physical mechanisms of the interaction between glass and safety film are not quite well understood, intensive research is conducted on the properties of this assembly. The loadings on the glass/film assembly are typically dynamic (blast, wind pressure, impact), so the lab tests are done on a drop weight set-up, where a mass is falling on a retrofitted glass plate. In this work, the drop weight setup was combined with pattern projection (moire) technique to study the time history of the out-of-plane deformations of the glass/film assembly. The fringe pattern, projected on the back side of the specimen, was generated by means of a sinusoidal phase grating under divergent high intensity infrared illumination. The whole process was recorded with a high speed camera. Local routines based on Fast Fourier Transform were used to process the captured images, and to extract the phase. The exact out-of-plane displacements were calculated by means of calibration based on previous shape measurements of several different objects with known dimensions.

The goal of this study is to apply photoelasticity for analysis of the mechanical behavior of thermoplastic polyester window security films. More specifically, the change of the photoelastic pattern for film samples with mechanical stress concentrators (holes and cracks) under tensile load is observed. For the purpose, the samples are covered with photoelastic birefringent PhotoStress® coatings. Being subjected to a tensile external load, the film transfers the strains over its surface to the coating. The latter are observed as interference fringes - isochromatic fringes, which exhibit the difference of the principal strains and isoclinic fringes, which characterize principal strains orientation. The photoelastic measurements were performed with a circular reflection polariscope with a white light and monochromatic illumination (575 nm). In the second case, two-loads phase-shifting technique is used for digital retrieval of isochromatics and isoclinics by successive acquisition of two pairs of four fringe patterns obtained at four different configurations of the optical elements of the polariscope. Since the specifics of the studied thermoplastic materials requires simultaneous recording of the phase-shifted patterns in the non-linear part of their loading curve, we propose an optical arrangement for real-time recording as a future development for solution of non-linear dynamic tasks.

The goal of the present paper is to develop a procedure for calculation of the fringe pattern in reflection for Fizeau interferntial wedge considering both positive and negative incidence at which the incident light beam undergoes multiple reflections within the wedge in direction of increasing or decreasing wedge thickness respectively. High-reflectivity coatings wedges with apex angle of 5 - 100 μrad and thickness of 5 - 500 μm are considered. To avoid the drawbacks of the plane-wave approximation and to calculate the interference pattern for a limited beam illumination at any distance from the wedge, we proposed a plane-wave expansion approach. We analyzed the wedge interaction with a Gaussian beam as a beam structure of particular importance in laser technique. In addition, an analytical solution of the involved integrals was obtained for the Gaussian intensity distribution. It was shown that both contra-incidences of the light beam could be described by the same mathematical expressions, i.e. the reflected fringe pattern at positive incidence could be considered as prolongation of the reflected pattern at negative incidence at some distance from the wedge. Experimental verification is also provided.

Absorption and fluorescent spectra are obtained in saturation regime of a single beam laser spectroscopy of Cesium D₂ line, in a vapor layer with thickness close to the light wavelength. We compare experimentally and theoretically obtained spectra distinguishing between open and closed, in terms of optical pumping, hyperfine transitions. In absorption, we observe a persisting difference between open and closed transitions, in terms of Dicke narrowing, when increasing laser light intensity. In fluorescence, for open transitions we note saturation dips which do not change significantly when increasing intensity. In case of closed transition, a small feature at the fluorescence line center appears for relatively high light intensity.

The work presents design and testing of a four-wavelength laser micro-refractometer for determination of refractive indices of liquid and solid thin films. The main goal is to achieve widening of the measured spectral region - from the violet end of the visible spectrum to the near infrared. Semiconductor lasers are used as light sources at wavelengths 406 nm, 656 nm, 910 nm and 1320 nm. Evaluation of the sample refractive index is based on critical angle determination by detection of vanishing of the diffraction pattern from a metal grating. The well known standard liquids as distillate water, ethanol, methanol, acetone and 1-bromonaphthaline are selected for approbation of the developed apparatus. The refractive indices, obtained at four wavelengths, are used to build the dispersion curves. For the purpose one-oscillatory Sellmeier's dispersion relation is chosen. Measurements at two wavelengths in the near infrared region enable more accurate description of dispersion curves. The obtained values of the refractive indices are compared to the values from other measurements made with a precise Pulfrich refractometer, in which Ar⁺ and He-Ne lasers have been used as light sources.

Doppler lidar continues to advance as a useful method for remote sensing of atmospheric winds. Applications from mobile and ship-based platforms have demonstrated the impact of coherent lidar observations for studying the structure of the stable and marine boundary layers. Airborne deployments enable observations over extended areas, and were used to measure water vapor transport over the US Great Plains. Recently, smaller coherent lidars operating at 1.6 μm have become commercially available. A new direct detection lidar currently will enable airborne observations in aerosol-sparse atmospheric regions. Efforts to extend Doppler lidar to space are underway in Europe, with a Doppler lidar winds mission planned for late 2010.

Aerosol and cloud optical properties are studied using data from ground-based sky radiometer measurements. We started the long-term monitoring of aerosols, cloud and etc by using a sky radiometer on SKYNET. We are seeking in this data information on the aerosol optical properties with respect to their temporal and spatial variability and validation of Satellite and numerical models.

An experimental campaign was carried out at Central Geophysical Laboratory at Belsk (Poland) in October 2007. Three sun photometers: Cimel CE-318, Prede POM-01L and Microtops II were used to obtain the atmospheric aerosol optical characteristics. Cimel CE-318 and Prede POM-01L are automatic sun-tracking devices common in the world networks for aerosol investigations AERONET and SKYNET. Microtops II is a hand-held manual device often used in field experiments because of its mobility. The results obtained show similar behavior of the aerosol optical depth variations and close values obtained by the three devices at the common wavelengths over rural area. The Microtops II readings are between the readings of the other two sun photometers. The experiment carried out is helpful and shows that the Microtops II sun photometer provides comparable results to these obtained by the Cimel CE-318 and Prede POM-01L sun photometers and potential of using Microtops II for measurement over an urban and rural area.

Aerosol structure measurements in the troposphere were carried out at the Arctic Lidar Observatory for Middle Atmosphere Research (ALOMAR), Norway, during summer 2007. ALOMAR troposheric lidar and Cimel CE-318 sun photometer were used to implement the aerosol measurements. Three wavelengths of the sounding laser radiation were used during the experiment λ₁=1064nm, λ₂=532nm and λ₃=355nm which brings additional information about atmospheric aerosol optical and microphysical characteristics in the whole troposphere. The experimental data could be arranged in two groups: days when Ci-clouds were observed (in June) and days when the meteorological situation is characterized with clear sunny weather (in the beginning of July). In days with presence of Ci-clouds two layers are observed in the planetary boundary layer-the first one with maximum height from 1500m to 2000m; the second one with maximum height from 2000m to 3000m. In clear sunny days few layers are observed with minimum height from 1500m to 2300m and maximum height around H=6000m. The height of the layers remains constant or decrease with time. The lidar data are juxtaposed with the data obtained by the sun photometer.

Within the framework of the project "EARLINET-ASOS (European Aerosol Research Lidar Network - Advanced Sustainable Observation System)" Contract No 025991 of European Commission's Framework Program 6 (EC FP6) (http://www.earlinet.org), transportation of Saharan dust over Europe has been observed in the sky over Sofia, during the last week of May, 2008. This phenomena, predicted by the Atmospheric Modeling and Weather Forecasting Group of National Technical University of Athens (NTUA) (http://forecast.uoa.gr/) and the Forecast system of Barcelona Supercomputing Center (BSC) (http://www.bsc.es/projects/ earthscience/DREAM), was interesting with its relatively long-time existence and large scale of propagation over the continent. In this work, we present the results and some comments of the measurements of the atmospheric backscatter coefficient made in Sofia, using aerosol lidar with CuBrvapor laser.

In this work, a combined Raman-elastic backscatter lidar is described. It is based on a Q-switched powerful frequencydoubled Nd:YAG laser (output pulse power: up to 1 J at 1064 nm; up to 100 mJ at 532 nm; pulse duration 15 ns FWHM; repetition rate 2 Hz). A Cassegrain telescope (35 cm diameter, 200 cm focal length) collects backscattered radiation from atmospheric particles and molecules. Lidar's spectral receiving module consists of three cannels. The first two channels separate and detect elastic-backscattered lidar signals at laser wavelengths 1064 nm and 532 nm, respectively. In the third lidar channel, a radiation at a wavelength of 607 nm is selected and detected, resulting from Raman backscattering of laser second harmonic (532 nm) by atmospheric nitrogen molecules. Experimental profiles of the aerosol backscattering coefficient demonstrating measurement abilities of the system are shown and discussed. Particularly, attention is paid to profiles containing signals from high-altitude cirrus clouds, low-altitude stratus clouds, hazy atmospheric areas and Saharan dust over the city of Sofia.

Remote-sensing technique (aerosol LIDAR), that provides a opportunity to investigate atmospheric boundary layer structure and determine the height of the mixing layer, was used. Simultaneous observations of the convective boundary layer development and surface ozone concentration dynamics between early morning and afternoon are presented. Contribution of the two processes (photochemical ozone formation and vertical advection) driven by increasing solar radiation to ozone content is analysed on the base of experimental data received during summer campaign of 2005 in Sofia, Bulgaria. Also, simultaneous diurnal surface ozone and meteorological parameters (temperature, solar radiation, wind speed and direction, relative humidity) measurements carried out during summer - spring time of 2006 are presented. An examination of the relationships between ozone and meteorological factors provided evidence for the processes defining observed ozone pollution.

In this work we developed a method for estimation of the ratio of aerosol to molecular backscattering coefficients in lidar sounding of the atmosphere. We presented our first results of such analysis of lidar measurement carried out in June- July 2008, using lidar system with a CuBr-laser and two receiving channels. The laser emits simultaneously two closely disposed wavelengths λ₁=510.6 nm and λ₂=578.2 nm of similar output powers. The spectral distance between these wavelengths provides well distinguished molecular scattering signal. From the other side the both wavelengths are too close to accept (in the first order of approximation) a similarity in the aerosol scattering conditions. Both lidar channels have very similar technical parameters (as overlapping functions, photon detector sensitivity, optical transmission, etc.) and thus, provide similar output signal levels for both wavelengths. The preliminary results from the analysis of experimental data demonstrated the opportunity to detect and to process well distinguished lidar signals in clear atmosphere. The operational heights exceed 9 km at accumulation time 30 min, that is typical for the adopted integration time in European lidar network EARLINET.

Two new approaches are proposed for determination by Thomson scattering lidar of the electron temperature in thermonuclear fusion plasmas. They are based on an analysis of the relativistic Thomson scattering spectrum. One of them is based on the unambiguous temperature dependence of the ratio of the return-signal powers of two spectral regions. The second approach is based on the unambiguous temperature dependence of the "center-of-mass wavelength" of the lidar-return spectrum. Analytical expressions are derived of the corresponding errors in the determination of the electron temperature. Their validity is confirmed by computer simulations. On the basis of the theoretical expressions a comparison is performed between the potential accuracies of the new methods and the routine fitting approach. As a result it is shown that the new approaches would have comparable efficiency with the fitting approach. Thus the three (the fitting and the novel) approaches may be used for mutually validating the results obtained for the electron temperature. They may be used as well for distinguishing the real inhomogeneities in the recovered temperature profiles from apparent ones due to statistical fluctuations. The novel approaches may also have some practical advantages consisting of the simple, clear and stable measurement procedure without any hypotheses or other considerations about the weight or the variance of the experimental data or the goodness of the fit.

Image data-handling technique using a Statistical Approach for measuring the velocity of inhomogeneities drifting in the atmosphere is suggested. Velocity measurements of imaged cloud fields have been conducted by gathering time-spatial realizations at equal time intervals. Properly selected data are used to develop the temporary instabilities for fixed dots of the field. The coordinates of the minimum value for every temporary instabilities are fixed. The cross-correlation function of two imaged cloud fields round these coordinates is calculated. The modules and the direction of the velocity vector are sets by the position of the global correlation maximum.

In this communication we present our first experimental results related to the measurement of the directional reflectance of some rock and mineral samples in the thermal infrared (TIR) band. A simplified experimental set-up is developed to assess the rock emissivity by means of sample reflectance data, measured at several view angles with respect to the normal to the studied surface and comparison with Lambertian surface. The experimental data have shown that most samples exhibiting a naturally rough surface reflect diffusively (close to Lambertian) the irradiating light. Their emissivity can be estimated using the measured values of the directional reflectance. Exceptions from the diffusion reflectance are made by some smoothly sawed dense samples which exhibit higher portion of specular reflection. The presented results could be of importance for the thermal remote sensing method applications, where the emissivity data are deduced from the measurement of the reflectivity of the objects.

Instrumental complex of remote souding in real-time on objects of organic origin is created. In this report the questions connected with application of the developed complex for remote monitoring in real time of objects of an organic origin of small volumes, down to traces are considered. Estimation of accuracy of measurements, ways of increase of sensitivity and lidar long-range action are considered. Opportunity of creation of self-trained system of recognition is discussed.

Biophotonics techniques are applied to several fields in medicine and biology. The laser based techniques, such as the laser induced fluorescence (LIF) spectroscopy and the optical coherence tomography (OCT), are of particular importance in dermatology, where the laser radiation could be directly applied to the tissue target (e.g. skin). In addition, OCT resolves architectural tissue properties that might be useful as tumour discrimination parameters for skin as well as for ocular non-invasive visualization. Skin and ocular tissues are complex multilayered and inhomogeneous organs with spatially varying optical properties. This fact complicates the quantitative analysis of the fluorescence and/or light scattering spectra, even from the same tissue sample. To overcome this problem, mathematical simulation is applied for the investigation of the human tissue optical properties, in the visible/infrared range of the spectrum, resulting in a better discrimination of several tissue pathologies. In this work, we present i) a general view on biophotonics applications in diagnosis of human diseases, ii) some specific results on laser spectroscopy techniques, as LIF measurements, applied in arterial and skin pathologies and iii) some experimental and theoretical results on ocular OCT measurements. Regarding the LIF spectroscopy, we examined the autofluorescence properties of several human skin samples, excised from humans undergoing biopsy examination. A nitrogen laser was used as an excitation source, emitting at 337 nm (ultraviolet excitation). Histopathology examination of the samples was also performed, after the laser spectroscopy measurements and the results from the spectroscopic and medical analysis were compared, to differentiate malignancies, e.g. basal cell carcinoma tissue (BCC), from normal skin tissue. Regarding the OCT technique, we correlated human data, obtained from patients undergoing OCT examination, with Monte Carlo simulated cornea and retina tissues for diagnosis of ocular diseases.

We apply a previously developed 3D Finite-Difference Time-Domain (FDTD) simulation method to model the optical phase contrast microscopic (OPCM) visualization of Gold nanoparticles (NPs) attached to the nucleus of a singe biological cell. We consider a realistic size 3D cell model at optical immersion conditions, i.e. when the refractive index values of the cytoplasm and of the extra-cellular medium are equal. The visual effect of the Gold NPs is studied at both resonant and non-resonant conditions. The results show that, at resonance, there are specific visual patterns that could be used for the identification of the presence of NPs at the nucleus' surface. The model demonstrates the capability to model the specific conditions of OPCM image enhancement by optically controlling the resonant properties of the NPs.

Photodynamic therapy (PDT) today is an innovative and not yet widespread light-drug initiated treatment that is based on the photoactive compound irradiated with proper light to produce oxygen species that are toxic to the pathogenic biological objects- bacteria, viruses, tumor cells. The obstacles that limited the efficacy of PDT concern to the selectivity and multi-drug resistance prolong time for cellular release and side effects of skin photosensitivity for commercial porphyrin originated photosensitizers (PS). Now there are very intensive investigations for introducing in practice a new, with a least side effects PSs for PDT. The usefulness of the more extended macromolecules structured with proper substituents refers not only to the improved optical properties like far-red and with intensive absorption and emission capacity, but mainly to the ability for selective delivery and adhesion to the target cells, such as bacteria or other pathogens. The present study focuses on the charge effect of photodynamic agent on the uptake capacity toward gram-negative bacteria cells and their further photoinactivation. The multi-drug resistant microorganism Aeromanas hydrophilla, which is causing diseases to fishes and humans, is treated. The new octa-cationic phthalocyanines are designed to compare PDT efficacy to the efficacy of tetra-substituted derivatives with the same functional peripheral substituents. The higher cellular accumulation to the bacteria cells as a result of the high number of positive charges of photosensitizer, leading to the better adhesion to the cellular membranes and improved photoinactivation of bacteria causing superficial and intraorgan infections. These results set a base of a rationale design of covalently octa-substituted phthalocyanines with positive charge for a successful treatment of microorganisms.

Light transport is currently used clinically both as a therapeutic tool and as a diagnostic tool. A concern in all these cases is the difficulty of knowing which regions of the tissues are sufficiently illuminated for therapeutic results, or from which regions the collected fluorescence was emitted. Development of optical models that explain the observed scattering properties of soft biological tissues is of considerable interest. Such modeling can give how the scattering properties are influenced by the numbers, sizes and arrangements of the tissue structure. In this article we give a brief overview of the laser light transport in tissue and also discuss some representative applications of tissue optics for biomedical applications.

The spatial parameters of scattered light in turbid media with different degrees of turbidity and at various depths are studied in this work. The measurements are made at two wavelengths (687 nm and 850 nm). A collimated laser radiation is used in the experiments in order to avoid the effect of input laser beam structure on the measured optical fields. The radial and in depth distribution is measured of the intensity of the forward-scattered optical beam radiation in turbid (tissue-like) media. The influence of small ingredients within the turbid media is also analyzed. The optical properties of the ingredients are different from those of the surrounding turbid medium. Milk-water mixtures are used as a test medium. The intensity distribution within milk solutions with concentrations ranging from 3.3% to 16.5% is measured in depth of more than 10 cm. The experimental results indicate that the presence of small ingredients within the phantom leads to characteristic changes of the intensity distribution. These preliminary results are evaluated as promising for developing a novel technique for determination of optical characteristics of small embedded ingredients in turbid media.

Delta-aminolevulinic acid / protoporphyrin IX is applied for exogenous fluorescent tumor detection in the upper part of gastrointestinal tract. The 5-ALA is administered per os six hours before measurements at dose 20mg/kg weight. Highpower light-emitting diode at 405 nm is used as a source and the excitation light is passed through the light-guide of standard video-endoscopic system to obtain 2-D visualization. Through endoscopic instrumental channel a fiber is applied to return information about fluorescence to microspectrometer. In such way 1-D detection and 2-D visualization of the lesions' fluorescence are received. The results from in vivo detection show significant differentiation between normal and abnormal tissues in 1-D spectroscopic regime, but only moderate discrimination in 2-D imaging. In the case of 2-D video visualization the problem of relatively high levels of the autofluorescence signal in the red spectral region gives low contrast between normal and abnormal mucosa when standard CCD camera of the endoscope is applied. Sensitized inflammatory areas also give to the observer in 2-D mode low contrast between malignant areas and benign tissues and finally the emission signals are additionally altered from the re-absorption of the chromophores accumulated in the tissue investigated. The possibilities for proper discrimination between normal, inflammatory and malignant tissues using 5-ALA/PpIX and both - advantages and limitations of 1-D and 2-D fluorescent detection modes are discussed in relation to their clinical applicability.

In this work, ablation experiments of ex vivo porcine cornea tissue were conducted with two solid state lasers (an Er:YAG laser and the 4th harmonic of an Nd:YAG laser, both in the ns pulse width range) emitting in mid infrared and ultraviolet part of the spectrum respectively, at moderate laser fluences. The cornea epithelium of each porcine eye was manually removed before the ablation. Histology analysis of the specimens was performed, in order to examine the microscopic appearance of the ablated craters and the existence of any thermal or mechanical damage caused by the midinfrared and the UV laser irradiation. For a detailed and complete examination of the morphology of the laser ablated corneal tissue, the surface roughness was investigated by scanning electron microscopy.

In this paper we report the results of measurement of the penetration of the radiation from different visible light emitting diodes (LEDs) inside dental tissue. The experiments are made using several different LEDs with wavelengths between 450 nm and 800 nm and power densities between 50 and 250 mW/cm2, which are the most frequently used in the clinical practice with proved clinical effect. The experimental results show that the penetration depends on the wavelength and the type of tissue. The results can be employed in the clinical practice for determining radiation dosage in the treatment of periodontal diseases.

We consider the generalized Gross-Pitaevskii models with varying nonlinearities from the point of view of their exact integrability and obtain the general solutions for these models both for confining and expulsive external potentials. We show that exact soliton solutions exist only under certain conditions and that varying in time nonlinearity and confining harmonic potential cannot be chosen independently; they satisfy the exact integrability conditions. The main features of nonautonomous matter-wave solitons near the Feshbach resonance with continuously tuned scattering length are investigated. We focus on the most physically important situations where the applied magnetic field is varying in time linearly and periodically. It is proved that near a Feshbach resonance the matter wave solitons can be stabilized even without a trapping potential. In the case of periodically varying interaction strength among atoms, variations of the external harmonic potential are found to be sign-reversal. The main difference from the canonical soliton case is that the matter-wave solitons management concept must be consistent with variations of confining potential.

We show that axicon-focusing of ultrashort laser pulses facilitates the generation of filaments with specific spatial profiles in the form of nonlinear Bessel beams. For conditions ensuring that the energy arriving from each Bessel ring is in quasi equilibrium with that absorbed by multiphoton processes, these Bessel filaments generate meter long plasma channels whereas the same pulses focused by a standard lenses generate plasma channels which do not exceed a few centimeters long. Measurements with different lasers show that the length and the homogeneity of the plasma channels are enhanced by the use of large beams and sharp-tip (ideal) axicons whereas blunt-tip axicons induce a lens effect leading to oscillations of the plasma density along the propagation axis.

Coherent rotational dynamics of gas-phase molecules induced by the excitation with an intense nonresonant ultrafast laser field is discussed. In particular, utilities of quantum-state resolved spectroscopic probe after the nonadiabatic rotational excitation (NAREX) by the ultrafast pulse(s) are described with some examples of double-pulse excitation experiments, which provided detailed information on excitation pathways and realization of full quantum-state reconstruction of a rotational wavepacket. Future prospects of the present method are briefly discussed.

Several methods for transforming the spatial properties of optical beams in nonlinear photonic crystals are reviewed. Successive up-conversion and down conversion a periodic 1D nonlinear photonic crystal enables to convert the fundamental Gaussian beam to a higher order Hermite Gaussian beam at the same wavelength. Nonlinear deflection over a wide spectral and temperature range is enabled by a specific two-dimensional modulation of the nonlinear coefficient. Finally, nonlinear generation of vortex beams can be achieved by specific three-dimensional modulation of the nonlinear coefficient.

We have developed a low cost apparatus for open- and closed-aperture Z-scan measurements of multi-photon absorption (MPA) cross-sections of solid and liquid samples. The experimental setup uses simple diodes for light detection. The signals are recorded with a low-cost two-channel PC-scope. We have developed a LabView based software, which analyzes single laser pulses and allows averaging over several shots. First measurements on a CR-39 polymer demonstrated the functioning of the method. Furthermore, we have shown that for 25fsec ultra short pulses three-photon absorption (ThPa) must be considered in addition to two-photon absorption (TPA). The appropriate nonlinear absorption (TPA-, ThPA-) coefficients and the nonlinear refractive index can be obtained via a best fit of the data to theoretical curves, which have been derived and adapted for ThPA from formulas for TPA accessible in the literature.

The dynamics of nonlinear solitary waves is studied in the framework of the nonlinear Schrodinger equation model with time-dependent confining harmonic oscillator potential. The model allows one to analyse on the general basis a variety of nonlinear phenomena appearing both in Bose-Einstein condensate, condensed matter physics and in nonlinear optics and biophysics. The nonlinear effect of the soliton parametric resonance is investigated by using two complementary methods: the adiabatic perturbation theory and direct numerical experiments. Conditions for reversible and irreversible denaturation of soliton bound states are also considered.

In the present work a quasilinear regime of propagation of three-dimensional short optical pulses in a dispersive medium has been considered. The small parameter method, developed by Bogolyubov, has been used to solve the equation, describing the evolution of such pulses. The relation between the approximate solution obtained, and the corresponding solution, describing a linear regime of short pulse propagation has been derived.

In this work, by using 4x4 ray-pulse matrices, we analyze the influence of the position of the output diffraction grating in 4f- and 2f-2f-systems with respect to the eventually introduced group-delay dispersion, spatial and angular chirp. We show that in the 4f-configuration, in contrast to the 2f-2f-setup, the grating offset does not cause angular chirp and pulse front tilt. We theoretically derive an expression for the interferometric autocorrelation signal in the presence of an arbitrary pulse-front tilt.

Efficient excitation of an ensemble of atoms and molecules to a desired state is of fundamental importance not only for spectroscopy but also for quantum control of molecular dynamics in chemical and biological processes. The latter usually occurs on a much shorter time scale (in the femtosecond range) giving rise to steadily advanced problem how to excite one of the nearby levels, even when they are well within the broad fs pulse spectrum. We propose a new effective method for selective excitation of atoms based on the atomic coherence and discuss a sensitive method to verify experimentally the proposed mechanism using the technique of quantum beating in pump-probe experiments.

An experimental study of coherent light diffraction by single layers composed of liquid-crystal (LC) micro-droplets dispersed in a transparent solid polymer matrix is reported. The LC droplets with a linear-gradient size distribution reach a mean diameter of several tens of micrometers and are organized in a planar two-dimensional film. The controllable size of the LC droplets in the layer can be used for an efficient control of both transmittance and diffraction of incident laser light.

We present experimental evidence of reduced diffraction for focused femtosecond laser pulses at input power well under the critical value of self-focusing. Unexpected stability of propagation is recorded even at very low input power, in deep linear regime. The shape of the pulses is more close to Gaussian one, and they admit spectral properties quite different than X waves. Nonparaxial model for explanation of the observed experimental results is suggested.

A three-wavelength laser microrefractometer has been assembled and standard liquids have been used for calibration of the experimental set-up. Refractive indices of polymer solutions of Polycarbonate, Polyarylate, Polyester, Nylon, Copolyester A and Copolyesters B are measured. Experimental results of the examined samples are obtained at laser wavelengths of 532 nm, 632.8 nm and 790 nm. A standard uncertainty of ± 2×10^-4 has been achieved applying gomiometric table with 1-arcmin resolution. Specific refraction of the investigated polymer materials and their solutions are determined. The dispersion coefficients of Sellmeier's and Cauchy's equation are calculated and comparative dispersion curves are illustrated.

This paper describes the method for determination of spectral characteristics stability for dielectric coating to possible changes of separate layers optical thickness offered by us. The entered criterion of stability synthesized coatings lays in a basis of a procedure. Value of the second derivative of optimized structure merit function on layer thickness in a point of the decision is offered as criterion of separate layer stability.

We show both theoretically and experimentally that cross-polarized wave generation (XPWG) is more efficient when the input fundamental beam propagates along the [011] direction in a cubic crystal than along the previously used [001] direction. With a [011]-cut BaF₂ crystal we measured the highest to date XPWG conversion efficiencies. We prove another very important advantage of the [011]-cut approach: weak induced phase mismatch and consequently no need for its compensation.

We study the ability of beams carrying mixed step-screw phase dislocations to guide and steer probe beams with nonzero transverse velocity. We report the first experimental demonstration of bright signal beam deflection by steering odd beams of finite length carrying such dislocation. The numerical simulations show that the beam deflection can be ruled by the geometry and orientation of the dislocation.

The third-order optical susceptibility of magnesium sulfite hexahydrate (MgSO₃.6H₂O) single crystal is experimentally studied by nonlinear laser spectroscopy. Third-harmonic generation (THG) and two-photon absorption (TPA) in this crystal are examined within the 600 - 1500 nm range by picosecond optical parametric oscillator (OPO). Some important characteristics of the crystal such as the THG efficiency, the value of the cubic susceptibility χ⁽³⁾, the dispersion of the third-order nonlinearity and the nonlinear refractive index (n₂), are determined.

We investigate nonlinear diffraction (NLD) of laser radiation in circularly poled nonlinear quadratic crystal for the case of single and two fundamental pump beams. We show that single pump beam excitation (10 ps @ 1.053 μm) along Z axis of circularly poled structure (with period 7.5 μm) leads to the second harmonic signal being emitted in a form of multiple low order cones (rings) and one strong external SH cone (ring) defined by the longitudinal phase matching conditions. We study a dependence of the NLD pattern as a function of the incidence angle of the pump. We demonstrate that two noncollinear pump beams intersecting exactly in the center of the structure results in a new type nonlinear diffraction, which does not have an analogue in linear optics. It features a set of nonlinearly diffracted beams originating from each individual pump accompanied by the set of additional diffraction rings which originate from photons coming from both pumps. The corresponding phase matching conditions responsible for the observed NLD effects are discussed. The observed effects represent nonlinear generalization of optical diffraction in linear media and we believe can find possible applications in second harmonic optical microscopy.

A novel design of reversed domains in a short-range ordered manner by placing randomly oriented basic units on a square lattice is propose and demonstrated. The corresponding reciprocal space is characterized not only by discrete diffraction peaks, but also by the continuous RVs distribution as homocentric rings. Then continuous nonlinear process is available as long as its wave vector mismatch falls within the region of continuous RV. In experiment the measured SHG tuning was so broad that it contains almost all frequencies in the visible range. The conversion efficiency was ~13% in the red and yellow wave bands, which is much higher than that generated in disordered NPC. Moreover, practically no any drop of the efficiency occurred even though the incident direction or sample temperature varies over a large range (50°C and 18°). Advantage of such a short-range ordered structure is demonstrated in collinear cascaded third harmonic generation (THG) at 1577 nm fundamental wavelengths.