This PDF file contains the front matter associated with SPIE Proceedings Volume 6604, including the Title Page, Copyright information, Table of Contents, Introduction, and the Conference Committees listing.

We review our previous work on pump-probe spectroscopy in realistic degenerate two-level systems and model systems. In particular, we discuss the role of transfer of coherence (TOC) between the ground and excited hyperfine states in producing electromagnetically-induced transparency (EIA) peaks in the probe spectrum, when an F_g goes to F_e = F_g +1 transition in an alkali-metal atom interacts with a strong pump and weak probe that have perpendicular polarizations. When the pump is rho⁺ polarized and the probe pi polarized, this system can be modelled by an N system. We also discuss the role of transfer of population (TOP) between the Zeeman levels of the ground hyperfine state in producing EIA peaks when the pump and probe have the same polarization. This system can be modelled using a double two-level system. The role of Doppler broadening and phase-changing collisions in modifying the EIA-TOC and EIA-TOP absorption and refraction spectra is also discussed. All these spectra were calculated using MATLAB programs that both construct and solve the relevant Bloch equations. In our recent work, we consider the effect of a strong probe on the pump absorption and refraction spectra when the pump and probe polarizations are linear and perpendicular. It is difficult to solve this problem numerically due to the large number frequencies involved. In order to simplify the problem, we considered two cases: (i) rho⁺ polarized pump and pi polarized probe, and (ii) rho⁺ polarized pump and rho^- polarized probe, and investigated a series of transitions in both Rb and Cs, using modified versions of the MATLAB programs devised for the weakprobe case. A number of interesting differences from the weak-probe case were found. For example, when the probe is sufficiently strong, we found the pump and probe spectra to show complementary behavior. In addition, as the number of Zeeman levels increase, the EIA peaks become progressively sharper, and are accompanied by steeper dispersion.

We provide an overview of our research on chip-scale atomic devices. By miniaturizing optical setups based on precision spectroscopy, we have developed small atomic sensors and atomic references such as atomic clocks, atomic magnetometers, and optical wavelength references. We have integrated microfabricated alkali vapor cells with small low-power lasers, micro-optics, and low-power microwave oscillators. As a result, we anticipate that atomic stability can be achieved with small size, low cost, battery-operated devices. Advances in fabrication methods and performance are presented.

We demonstrate a magnetometric technique based on nonlinear magneto-optical rotation using amplitude modulated light. The magnetometers can be operated in either open-loop (typical nonlinear magneto-optical rotation with amplitude-modulated light) or closed-loop (self-oscillating) modes. The latter mode is particularly well suited for conditions where the magnetic field is changing by large amounts over a relatively short timescale.

Electromagnetically induced transparency (EIT) resonance, along with peculiarities of the accompanying velocity selective optical pumping/saturation (VSOP) resonances, have been studied using a thin cell with the thickness of Rb vapor column varying in L = 10-700 &mgr;m range, as well as using an extremely thin cell (ETC) with the thickness varying in the range of radiation wavelength &lgr; = 780 nm (L = 0.5&lgr; - 2.5&lgr;). The &Lgr;-systems on D₂ line of ⁸⁵Rb and ⁸⁷Rb have been studied experimentally with the use of bichromatic radiation of two separate diode lasers. It is demonstrated that size-conditioned strongly anisotropic contribution of atoms with different velocities in ETC results in several dramatic distinctions in formation of EIT and VSOP resonances in ETC, as compared with ordinary cm-size cell. The boundary between these two regimes falls on L ~ 10 &mgr;m. Theoretical model taking into account the peculiarities of the transmission spectra as a function of the ratio L/&lgr; is developed. The experimental transmission spectra are well described by the theoretical model.

This paper presents our current measurements in a vapor nanocell aiming at a test of the distance-dependence of the atom-surface interaction, when simple asymptotic descriptions may turn to be not valid. A state-of-the-art of atom-surface interaction measurements is provided as an introduction, along with the comparison with the theory of the van der Waals (or Casimir-Polder) interaction; it is followed by a presentation of the most salient features of nanocell spectroscopy.

The study of light induced processes on atoms and nanoparticles confined in organic films or in dielectric structures is motivated both by fundamental interest and applications in optics and photonics. Depending on the light intensity and frequency and the kind of confinement, different processes can be activated. Among them photodesorption processes have a key role. Non thermal light induced atomic desorption has been observed from siloxane and paraffin films previously exposed to alkali vapors. This effect has been extensively investigated and used both to develop photo-atom sources and to load magneto-optical traps. Recently we observed huge photodesorption of alkali atoms embedded in nanoporous silica. In this case the atomic photodesorption causes, by properly tuning the light frequency, either formation or evaporation of clusters inside the silica matrix. Green-blue light desorbs isolated adatoms from the glass surface eventually producing clusters, whereas red-near infrared (NIR) light causes cluster evaporation due to direct excitation of surface plasmon oscillations. Green-blue light induces cluster formation taking advantage of the dense atomic vapor, which diffuses through the glass nano-cavities. Both processes are reversible and even visible to the naked eye. By alternatively illuminating the porous glass sample with blue-green and red-NIR light we demonstrate that the glass remembers the illumination sequences behaving as an effective rereadable and rewritable optical medium.

We present an overview of the quadratic Stark effect in the ground state of alkali atoms. On the basis of symmetry arguments we show that the second order Stark interaction vanishes in the spherically symmetric S_1/2 ground state while an extension of the perturbation theory to third order, including the hyperfine interaction, leads to scalar and tensor polarizabilities. We discuss the effect on the hyperfine structure of the Cs ground state. We report 2 new independent measurements of the tensor polarizability &agr;₂⁽³⁾ (F = 4), which are in very good agreement with prior experiments, and we present an extension of the theory of the Stark interaction which bridges a 40 year old discrepancy between experimental and theoretical values of the tensor polarizability. We also report the presence of a sign error in prior theory and discuss its relevance for primary frequency standards.

Brownian motors are devices which "rectify" Brownian motion, i.e. they can generate a current of particles out of unbiased fluctuations. Brownian motors are important for the understanding of molecular motors, and are also promising for the realization of new nanolelectronic devices. Among the different systems that can be used to study Brownian motors, cold atoms in optical lattices are quite an unusual one: there is no thermal bath and both the potential and the fluctuations are determined by laser fields. In this Lecture notes recent experimental implementations of Brownian motors using cold atoms in optical lattices are reviewed.

A fully automated magnetometer suitable for long lasting measurement under stable and controllable experimental conditions has been implemented. The device is based on Coherent Population Trapping (CPT) effect produced by a multi-frequency excitation. It has an all optical sensor connected only by an optical fiber to the laser head. This allows truly remote sensing and minimization of the field perturbation. The CPT resonance is observed when a frequency comb, generated by a diode laser current modulation, excites a sample of Cs atoms confined in a cell with 2 Torr of buffer gas. In differential sensor configuration, allowing for common-mode noise cancellation, the sensitivity of 45pT/square root of Hz is obtained.

Spontaneous transfer of coherence has proven to be a good interpretative scheme for the explantation of the spectra of a probe laser probing a closed degenerate two-level systems. With its aid it was possible to give an explanation for the emergence of electromagnetically induced absorption and also to make predictions on the associated coupling laser spectra. Here we extend our work on the role of the coupling laser in electromagnetically induced absorption presenting new measurements of the probe and coupling laser absorption and dispersion spectra - taken in the D₂ line of caesium - which reassert the importance of spontaneous transfer of coherence in the generation of electromagnetically induced absorption spectra. All measurements were performed with linearly polarised coupling and probe laser of orthogonal polarisation, acting on a perpendicularly propagating caesium atomic beam to minimise the Doppler broadening of the lines. For sake of completeness we compared the electromagnetically induced absorption spectra with electromagnetically induced transparency spectra obtained in another two-level system within the same line. The measured probe spectra were used to calculate the refractive index of caesium in the presence of electromagnetically induced transparency and absorption. On that basis we could calculate the effect of Kerr nonlinearities and measure nonlinear Kerr coefficients of the order of n₂ ≈ 10^-5 cm²/mW with absorption coefficients of the order of &agr; ≈ 0.1 cm^-1.

In this communication we present our results related to examination of Coherent Population Trapping resonance profile on the D₁ line of ⁸⁷Rb when coupling two ground-state Zeeman sublevels belonging to different hyperfine ground-state levels to a common excited-state one. For this, two coherent laser fields with frequency difference of about 6.8 GHz are used. The resonance is observed as a narrow dip in the fluorescence in dependence on the modulation frequency (f_m) of the laser light, centered at 2f_m = &Dgr;v_hf , where &Dgr;v_hf is the frequency difference between the ground-state hyperfine levels of Rb. The resonance observation and its splitting in 7 components have been demonstrated under influence of nonshielded laboratory magnetic field (MF). It has been shown that different components are with different sensitivity to the MF gradients that is in agreement with the performed estimations.

We have studied experimentally and theoretically Hanle EIA on the closed F_g = 3 goes to F_e = 4 D2 transition of ⁸⁵Rb. Atoms were excited by the laser light with different polarization, from linear to circular. Results of the theoretical calculations of the laser transmission, based on optical Bloch equations for density matrix elements for the same atomic system, show important effects of magnetic field transverse to the laser light. We were not able to control transverse magnetic field in the experiment but the theoretical results are still applicable to our experimental data due the presence of laboratory stray magnetic field in the vicinity of the Rb cell, occurring because of imperfect magnetic shielding.

We have measured non-linear Faraday effects for dark and bright long-lived Zeeman coherences in the D2 resonance line of ⁸⁵Rb, for linearly polarized input laser light. Zeeman coherence in the bright state show enhanced nonlinear effects, larger values for the angle of polarization rotation and higher rates of the polarization rotation, similar to recent results for higher refractive index and dispersion in the bright state of Cs ¹. Dark and bright states also show different dependence of both polarization rotation angle and of polarization rate on the laser intensity, while the resonance width for both states varies similarly with the laser intensity. We show small enhancement of such non-linear effects when the laser beam diameter increases from 1 mm to 5 mm. Ellipticity of transmitted laser beam vary strongly for amplitudes of the external magnetic field smaller then 50 mG, but the maximum value of the ellipticity remains below &pgr;/300.

We discuss experimental and theoretical studies of coherent excitation of magnetic sublevels in nD states of cesium that cross in an external electric field. Crossings of m_F magnetic sublevels of hyperfine F levels with &Dgr;m_F = ±2 lead to resonances in the linearly polarized laser induced fluorescence, while crossings with &Dgr;m_F = ±1 lead to resonances in the circularly polarized laser induced fluorescence. These resonances can be exploited to observe alignment to orientation conversion. From the level crossing signals it is possible to measure atomic properties, such as the tensor polarizability &agr;₂ and the hyperfine constant A. Alignment to orientation conversion involves the deformation of the spatial distribution of an atom's angular momentum.

In this communication we present an investigation of the influence of an alternative magnetic field (a.c.MF) on the Coherent Population Trapping (CPT) resonances obtained in Hanle configuration. A.c.MF applied parallel to the sweeping magnetic field creates side-bands of the CPT resonance ¹. Their position in dependence on the a.c.MF frequency and amplitude were investigated. This phenomenon was studied for the cases of linear and circular polarized laser excitation. Coherent signal due to the hexadecapole momentum created was detected. At high amplitudes of the a.c.MF alignment to orientation conversion was recorded.

Numerical simulations are used to obtain the amplitudes and the widths of the nonlinear resonances related to the different ranks of the tensor components &rgr;^k_q in dependence on the atomic system parameters, and the laser field power (Rabi parameter - d.E/ℏ). The main attention is paid to the effect of the velocity distribution of the atoms on the hexadecapole (k = 4) components and their influence on the fluorescence and/or absorption signals. A detailed examination of our basic equations allows us to directly find out a relation between different rank components for a chosen transition and to clarify their role in the observed resonances for a given geometry.

Comparative studies of MO resonances and MG responses with and without resonant laser irradiation were carried out to establish the interconnection of the effects and the influence of the self-alignment destruction on the MO signal in positive column discharge. These studies aim to clarify the possible formation mechanisms of the neon 1 s_i (2p⁵3s) states coherences and to examine the possibility to use the galvanic resonances for estimation of the relaxation constants of the neon 1 s₅ state.

We present preliminary results showing that some noise sources in vapor cell atomic clocks based on coherent population trapping (CPT) can be suppressed with differential detection. The scheme we propose differs from more conventional differential detection in that both optical fields pass through the alkali vapor cell but have different polarizations, one circular and one linear. Because CPT resonances are only excited by the circularly polarized beam, the linearly polarized beam can be used to reduce several important sources of noise. With this technique, we demonstrate reduction of the short-term frequency instability of a CPT atomic frequency reference by a factor of about 1.5.

A diode laser system for spectroscopy of cold Rb atoms is reported. The apparatus is mainly aimed at studying the electromagnetically induced transparency (EIT) in cold environment. The system is based on a rubidium magneto-optical trap (MOT). Two additional extended cavity diode lasers provide the light beams for experimenting, e.g., a coupling- and probe- beam for EIT. The set-up is equipped with channels for detection of absorption and fluorescence. Some system elements of the ones made in our laboratory, in particular, the electronic system for data acquisition and for control of MOT and experiment, are presented in some detail. Records of probe beam absorption spectra of cold Rb, exhibiting profiles due to EIT in multilevel cascade scheme, registered by the use of this apparatus, are presented as an example of the setup performance.

We established an experimental set-up that allows laser stabilization using the Doppler¹ and sub-Doppler^2,3 Dichroic Atomic Vapor Laser Locking (DAVLL) and the Saturated Absorption (SA) scheme. In this report we present comparative studies between Doppler and sub-Doppler DAVLL using heterodyne frequency stability measurements with an independently SA stabilized laser. Some major sources of frequency instability are discussed together with ways to improve the stability. Special focus is laid on the sub-Doppler DAVLL stabilization technique where a new approach for getting higher stability is introduced. In our measurements, the ⁸⁷Rb D₁ line was used as reference atomic line.

We have studied the loading of a single-beam or a crossed dipole trap made by a Nd:YAG laser. The loading was performed from a magnetic trap or after a molasses phase with cesium atoms. Looking for high atomic density to perform a fast evaporation to reach the Bose-Einstein Condensation, we found that a crossed dipole trap with a waist of 30 &mgr;m and a laser power P=10 W, loaded from a molasses, gives a good starting point to begin evaporation with 5 &|m~; 10⁶ atoms loaded in 50 ms.

Experimental branching fractions for laser lines arising from excited states of 5d⁹7s configuration of Au II have been determined by application of Laser Induced Breakdown Spectroscopy (LIBS). The experimental relative transition probabilities were converted into an absolute scale using theoretical values for the radiative lifetimes of the corresponding states, calculated in this work. Transition probabilities and radiative lifetimes have been determined by a relativistic Hartree - Fock method taking configuration interaction and core-polarization effects into account. A comparison of the present results with the available theoretical values has been made and shows a reasonable agreement although discrepancies are observed between theory and experiment for some transitions.

A new lecture demonstration experiment for illustrating the wave-particle dualism of light is proposed. The equipment is based on the interference of two coherent light beams produced in a Mach-Zehnder interferometer. Light from a green laser pointer is used to perform two simultaneous experiments. The expanded laser beam traverses a Mach-Zehnder interferometer, which allows one to create a superposition of two coherent beams and to adjust the period of their interference fringes in a simple way—a didactic tool to illustrate the wave nature of light. The main feature of the experiment is the use of the same equipment to demonstrate the particle nature of light. For this the entering beam is strongly attenuated and photons at the exit of the interferometer are detected by a photomultiplier (PM) with a narrow slit, connected to a speaker. We propose a realization in which both of these experiments can be demonstrated simultaneously. Special design criteria of the set-up are its low cost, its simplicity, its didactical power and its suitability for large lecture halls.

Modification of Koester's interferometer is described in this paper, which is used for calibration of gauge blocks up to 100mm in length. Higher precision was obtained by using a camera (for measurement of fringe fractions) and lasers as the source of light. The process of digitalization and processing of the interference pattern images is also described, as well as rejection of noise caused by transmission of laser beams through the optical fiber.

Microlens and microlens arrays have been successfully produced using sensitized gelatin and Nd:YAG laser at 532 nm. Obtained microlenses are divergent (negative), with parabolic profile and 600 &mgr;m useful aperture diameter. Microlenses have near diffraction limited performance with resolution more then 50 cycles/mm for the total field of view (2&ohgr; = 18°). Single microlens is manufactured in just a few seconds using 60 mW unfocused Nd:YAG laser beam.

In this paper we describe a simple interferometric phasemeter which can be used as a linear sensor. This method is based on the interferometric restoration of both p- and s-components of the resultant field. The phase shift between them as a function of the attenuation of the total internal reflection can be determined from the interference signal. A lateral fringe shift and contrast variations were observed during the measurements. To explain these effects a simple theory is proposed. The resulting interferometrical signal is studied experimentally.

The characterization of a plasma plume is a key issue in laser ablation and deposition studies. Combined diagnostic measurements by Optical Emission Spectroscopy, Fast Imaging have been used to study the dynamics and composition of laser ablation plume produced during ultrashort laser irradiation of metals, in vacuum. Our results show that, in the laser fluence range of 0.1-1.0 J/cm², the process of matter removal results in a plasma plume which is mainly composed of two different populations: atoms and nanoparticles. The nanoparticles dynamics during expansion has been analyzed through their structureless continuum optical emission, while atomic species have been identified by their characteristic emission lines. The presence of a fast atomic component emitted from the sample surface as a result of the supercritical state induced by the intense ultrashort laser pulse irradiation has been also observed both by optical emission spectroscopy and fast imaging techniques. Finally, atomic force microscopy analysis of the material deposited at room temperature has allowed the characterization of the nanoparticles size distribution.

Results of the recent application studies of laser-based techniques for conservation practice, carried out in the frames of research and conservation projects are presented and discussed. The Gotland Sandstone Project covers laser cleaning, spectroscopic techniques of the process monitoring and materials analysis. The post-processing effect is investigated by means of LIBS, colorimetry, SEM and XEDS in order to answer questions regarding encrustation removal, discoloration and alteration due to environmental pollution and laser interaction, respectively. The cleaning is monitored acoustically. Slight differences in stone yellowing are revealed when applying laser in air or pure N₂ environment which is ascribed to material oxidation and partial combustion of surface remnants due to presence of O₂ contributing to the final effect of laser cleaning. Results of microscopic observation are supported by the presence of elements S, Al, Ca, and C which prevail in crust. In case of restoration of the historical documents on paper the ablative cleaning and the nearly nondestructive identification and composition analysis of surface layers such as contaminants, substrate and pigments are performed. Spectra obtained by means of the LIPS technique for historical, originally contaminated and also artificially soiled model samples reveal reach structures. The emission lines of Ca, Na, K, Al and Fe are ascribed to contaminants because of intensities decreasing with prolonged surface irradiation during laser cleaning. Bands of Ti and Ba correspond to white pigments (TiO₂ and BaSO₄) in the paper and are confirmed by the Raman spectra as well. For identification of historical pigments the reference measurements on model substrates are performed, too.

Thin films of various organic materials have been deposited by Matrix Assisted Pulsed Laser Evaporation (MAPLE) technique. The principles, advantages, and difficulties of deposition technology are discussed. The focus is on target preparation, solvents, studied materials, growth rate and films properties characterization.

High-quality crystals of KLu(WO₄)₂, shortly KLuW, were grown with sizes sufficient for characterization of the thermomechanical and optical properties, and substantial progress was achieved in the field of spectroscopy and laser operation with Yb³⁺- and Tm³⁺-doping. We review the properties of flux grown KLuW, the Yb³⁺ and Tm³⁺ spectroscopy, and present laser results obtained in several operational regimes both with Ti:sapphire and direct diode laser pumping using InGaAs and AlGaAs diodes near 980 and 800 nm, respectively. The slope efficiencies with respect to the absorbed pump power achieved with continuous-wave (CW) bulk and epitaxial Yb:KLuW lasers under Ti:sapphire laser pumping were ≈57 and ≈66%, respectively. Output powers as high as 3.28 W were obtained with diode pumping in a simple two-mirror cavity where the slope efficiency with respect to the incident pump power reached ≈78%. Passively Q-switched laser operation of bulk Yb:KLuW was realized with a Cr:YAG saturable absorber resulting in oscillation at ≈1031 nm with a repetition rate of 28 kHz and simultaneous Raman conversion to ≈1138 nm with maximum energies of 32.4 and 14.4 &mgr;J, respectively. The corresponding pulse durations were 1.41 and 0.71 ns. Passive mode-locking by a semiconductor saturable absorber mirror (SESAM) resulted in bandwidth-limited pulses with duration of 81 fs (1046 nm, 95 MHz) and 114 fs (1030 nm, 101 MHz) for bulk and epitaxial Yb:KLuW lasers, respectively. Slope efficiency as high as 69% with respect to the absorbed power and an output power of 4 W at 1950 nm were achieved with a diode-pumped Tm:KLuW laser. The tunability of this laser, under Ti:sapphire laser pumping, extended from 1800 to 1987 nm. An epitaxial Tm:KLuW laser provided slope efficiency as high as 64% and a tuning range from 1894 to 2039 nm when pumped by a Ti:sapphire laser.

The political problems in Late Roman Empire caused significant changes in the coin technology. The silver content dropped severely and a new technology, in all the mints operating around the Empire, was introduced. For the production of these coins, copper based quaternary alloys were used and their surface was covered by a silver amalgam plating layer. Hoards of these coins have been recovered in thousands from across the Empire, however, their treatment has been problematic. Both mechanical and chemical cleaning results in the damage or the complete destruction of the thin silver layer. The use of laser technology in the cleaning of works of art has a wide range of applications which includes metallic objects. The main aim of this work was to investigate the use of lasers in the cleaning of the thin silver plating layers found in late Roman coins. The optimisation of laser parameters was achieved through comparative cleaning tests by employing Nd:YAG (532 nm and 266 nm) laser systems. The cleaning results on the plated areas were characterised by optical microscopy, and SEM-EDX analysis. Following a systematic investigation and many cleaning trials on two different wavelengths and fluence values, optimum irradiation parameters were thoroughly demonstrated. Microscopic observations of the cleaned areas evidenced complete removal of the encrustation and high selectivity of the laser cleaning. Neither thermal or mechanical injuries, nor cuprite blackening were observed on the cleaned surfaces at the optimum laser cleaning technique, using 532 nm of the Nd: YAG laser.

The use of lasers in materials processing is an increasingly attractive choice for high technology manufacturing. Factors influencing the laser ablation process include laser beam parameters, such as wavelength, energy or fluence and pulse length, the material properties of the target, such as melting temperature, thermal diffusion rate, optical reflectivity, and the ambient gas. We investigated the influence of laser treatment on titanium wafers with CuBr laser (&lgr;=511nm) by scanning laser beam with distance between paths 20&mgr;. The laser fluence varied from 4.7 J cm^-2 to 13.5 J cm^-2 and the laser beam scanning velocity from 25mm/s to 100mm/s with duration of 30 ns. The experiments were done in two kinds of ambient atmosphere: air and argon. The morphology of the irradiated surface was studied by scanning electron microscopy (SEM). SEM study showed that the laser irradiation caused a change in the surface morphology due to the processes of melting and subsequent resolidification as well as particle deposition from the vapor plume. The chemical state and composition of the irradiated titanium surface were determined using the Ti2p and O1s binding energy values and O/Ti intensity ratio. The XPS results indicated that on the irradiated titanium surface is formed oxide layer with stoichiometry close to TiO₂. It was found that the ambient atmosphere is responsible for the change in the microstructure and chemical state of the titanium target.

A comparative investigation on the discharge and output parameters of the He-Zn⁺ laser excited by nanosecond and microsecond pulsed longitudinal high-current discharges is reported. A steady-state laser operation at the 610.2, 491.2, and 492.4 nm Zn⁺ lines is obtained with both discharges. The optimal discharge conditions, such as operating temperature, helium buffer-gas pressure, and discharge current amplitude, are found for each discharge.

M²-factor of the master-oscillator power-amplifier (MOPA) CuBr laser emission compliant with ISO 11146 is studied for first time. M² is an invariant that gives how many times diffraction-limited is a laser beam compared to a perfect Gaussian TEM₀₀ beam. Statistical parameters of the near and far fields of MOPA laser radiation are measured by a beam analyzing technique. Two patterns of the MOPA laser emission are examined: annular that is typical for lasers without addition of hydrogen, and of filled-center (top-hat and Gaussian-like) with addition of hydrogen. 2D intensity profile changes of the near and far fields are recorded as functions of delay time of laser excitation current pulses. The MOPA gain curve is found and the influence of gain on the input signal (from MO into PA) due to the absorption/amplification in PA on the field profiles is shown. The change of position and waveform of laser pulses is given too. For annular radiation M² range is from 13-14 (small delays) to 5-6 (large delays) and for filled-center radiation M² is 6-7 (small delays) and at the end of gain curve is as much as 4.

An investigation of a strontium bromide vapor laser excited by a nanosecond pulsed longitudinal discharge is presented. The optimal discharge conditions for laser oscillation on several Sr atom and ion lines are found. At multiline output an average laser power of 2.4 W is obtained, more than 80 % of which is concentrated at the 6.45-μm Sr atom line.

The increasing demands for miniaturization and better functionality of electronic components and devices have a significant effect on the requirements facing the printed circuit board (PCB) industry. PCB manufactures are driving for producing high density interconnect (HDI) boards at significantly reduced cost and reduced implementation time. The interconnection complexity of the PCB is still growing and today calls for 50/50 μm or 25/25 μm technology are real. Existing technologies are unable to offer acceptable solution. Recently the Laser Direct Imaging (LDI) technology is considered as an answer for these challenges. LDI is a process of imaging electric circuits directly on PCB without the use of a phototool or mask. The exposure of the photo-sensitive resist is carried out using a laser beam that is scanned across photoresist surface and switched on and off by means of a computer control system according to the electrical circuit pattern. Usually the laser used in the LDI generates a UV line, which is suitable to the commonly available photoresists. In this paper we present the laboratory system for Laser Direct Imaging and also the recent results on imaging the circuitry pattern on the PCB covered by a photosensitive resist.

In this work results of the laser visualization of the gas bubbles flow in a needle-to-cylinder pulsed discharge reactor filled with distilled water are presented. The experimental setup consisted of a pulsed discharge reactor, high voltage supply, CuBr laser, and Video camera. In the glass reactor bottom a stressed needle or a set of needles were placed. The grounded cylinder was set 45 mm above the needle electrode(s). The pulses of positive voltage (up to 31 kV) with a repetition rate of 50 Hz were used. A laser beam emitted from the CuBr laser was formed, using a telescope, into the laser sheet, which crossed the reactor in a selected vertical and horizontal plains. It was observed that during the positive pulsed discharge in water the bubbles production and the streamer size increased with increasing applied voltage. Large vortices generated during the discharge distributed bubbles in the whole reactor volume, providing good mixing and distribution of active species. The more needles were used, the larger number of bubbles were observed.

Simultaneous generation of several wavelengths in a steady-state distributed feedback (DFB) laser on jelly-like dyedoped gelatin is reported. It is shown that such lasing regime of the device is possible when a set of the stationary spatial gratings of different periods is prerecorded in the same volume of its active medium. Holographic characteristics of the employed photosensitive medium have been studied. The 2nd harmonic radiation (&lgr; = 532 nm) of the nanosecond (&tgr;_0.5 ≈ 17 ns) YAG:Nd laser was used for recording the gratings. The obtained holograms were readout with the help of a single-mode He-Ne laser radiation. Both picosecond and nanosecond YAG:Nd lasers were used for DFB laser excitation. The stable multiwavelength operation of a DFB laser at two and three narrow spectral lines simultaneously was obtained. The minimum and maximum clearance between simultaneously emitted spectral lines was measured to be ~ 0.09 and ~25 nm, respectively, at spectral width of separate lines of ~ 0.01 nm.

In this paper a Particle Image Velocimetry (PIV) measurement technique and it's application for the flow patterns measurements in our experiments is presented. Present PIV system consist of double Nd:YAG laser with pulse energy of 50 mJ, optics for transmission and formation a laser beam, two CCD cameras (Kodak MegaPlus ES-1.0 and FlowSense M2), Dantec processor PIV 1100 and PC computer with FlowManager software. The maximum measured area is 0.5 m² and flow velocity in the range of 0-300 m/s. So far, the PIV measurements were carried out in hydrodynamic and transonic ducts, corona discharge reactors, electrostatic precipitator models and a microwave torch discharge reactor in The Szewalski Institute of Fluid Flow Machinery, Polish Academy of Sciences in Gdansk. The PIV system was used also for the measurements of the velocity fields round the hull of the ship model in The Ship Design and Research Centre in Gdansk.

The aim of our work was to produce and investigate vanadium doped ZnO thin films with potential application in spintronic technology. Thin films with different concentration of V (2, 3, 5 and 7 at.%) were deposited by using the pulsed laser deposition (PLD) technique. The distribution of vanadium in the films and the variation of its content during laser deposition was determined by Rutherford backscattering spectroscopy (RBS). We also present a comparative study of the structural and electrical properties of 2 at.% V:ZnO films deposited on sapphire substrates with different orientations.

We present a contribution to the development of the laser heterodyne method of nondestructive material analysis employing photothermal displacement (PTD) probe. PTD is a dominant factor of the photothermal effect in metals and semiconductors, where the derived linear dependence on absorbed energy exhibits a fingerprint of their physical properties. Theoretical consideration of the case of transparent probe is accomplished extending thermal diffusion model. Laser double heterodyne detection is verified for opaque and transparent probes, and in the exclusive case of silicon. The achieved resolution of photothermal displacement is less than 10^-12 m well above the limits of heterodyne measurement.

Discrete optical phenomena occur in one dimensional periodic arrays of parallel coupled waveguides. Coupling between adjacent waveguides leads to a novel form of "discrete" diffraction, periodic dispersion relations involving multiple bands, and contain regions of both normal, anomalous and zero diffraction. This in turn impacts many linear diffraction phenomena, for example the Talbot effect. It also results in a diversity of phenomena in nonlinear optics including novel types of spatial solitons, beam break-up also known as filamentation, and solitonic interactions. The fundamental concepts are reviewed here and interesting examples of discrete optical phenomena discussed.

We show that the methodology based on the generalized inverse scattering transform (ST) provides a systematic way to discover the novel exactly integrable nonlinear Schroedinger equation modesl with varying dispersion, nonlinearity and gain or absorption. Novel soliton solutions for the nonautonomous nonlinear Schrodinger equation (NLSE) models with harmonic oscillator potential substantially extend the concept of classical solitons and generalize it to the plethora of nonautonomous solitons that interact elastically and generally move with varying amplitudes, speeds and spectra adapted both to the external potentials and to the dispersion and nonlinearilty variations. The nonautonomous soliton concept is a useful tool in optical solitons applications and opens novel possibilities for matter-wave solitons generation.

An optical model based on two linearly coupled Bragg gratings, with equal periodicities and a phase shift Theta between them (mismatch) is considered. For Theta = 0, the symmetry-breaking bifurcation of gap solitons (GSs) in this model was investigated before. The objective of the present work is to study an effect of the mismatch on families of symmetric and asymmetric GSs, and bifurcation between them. It is found that the system's bandgap is always completely filled with solitons. The largest velocity of moving solitons, ^cmax, is found as a function of Theta and coupling constant. The mismatch transforms symmetric GSs into quasi-symmetric (QS) ones, in which the two components are not identical, but their peak powers and energies are equal. The QS solitons are stable against symmetry-breaking perturbations as long as asymmetric (AS) solutions do not exist. In addition, the mismatch breaks the spatial symmetry of the GSs, separating peaks in the two components of the soliton, and giving rise to side hump(s) in them. If Theta is small, stable AS solitons emerge from their QS counterparts through a supercritical bifurcation. However, for a larger mismatch, the bifurcation may become subcritical. A condition for the stability against oscillatory perturbations is essentially the same as in the ordinary grating: both QS and AS solitons are stable, in this sense, if their intrinsic frequency is positive, i.e., they are stable in a half of the bandgap.

Nonlinear photonic crystals are materials in which the second order susceptibility is modulated, while the linear susceptibility remains constant. In this paper, quasi-phase matching possibilities in several different nonlinear photonic crystals are analyzed and compared. A periodic one-dimensional structure is usually employed for phase matching a single process, but we show that two processes can also be simultaneously phase matched by non-collinear interaction. Two-dimensional periodic modulation provides additional extension of the phase matching possibilities. The dependence of the process conversion efficiency on the specific choice of lattice, nonlinear motif and quasi-phase-matched order is analyzed. Further extensions are provided by quasi-periodic schemes. A very powerful method for designing quasi-periodic nonlinear structures, with either one-dimensional or two-dimensional modulation, is the socalled dual-grid method. This method practically enables to phase matched any set of nonlinear interactions, in any chosen direction of propagation. Finally, frequency conversion using a converter with pure rotation symmetry is analyzed and demonstrated.

We review our experimental development in the field of optical lattices, emphasizing their unique properties for control of linear and nonlinear propagation of light. We draw some important links between optical lattices and photonic crystals, pointing towards practical applications in the fields of optical communications and computing, beam shaping, and bio-sensing.

The propagation of solitons along the interface between two dielectric nonlinear media was investigated theoretically extensively in the 1980s but never realized experimentally. Recently we predicted that the required small index differences between the media and hence solitons can be created at the interface between continuous and periodic discrete media consisting of arrays of weakly coupled waveguides. Our theoretical analysis has predicted the existence of stable solitons with power thresholds both in the centre and at the edge of the Brillouin zone. We have observed both of these discrete surface solitons with power thresholds in both Kerr and quadratically nonlinear media. Spatial solitons with fields in neighboring channels either in phase or pi out of phase with one another have been identified.

A new method of realization of coupled nonlinear optical interactions in single aperiodically poled nonlinear crystal is studied. The simultaneous two and three coupled wave processes are investigated in detail.

Novel χ⁽³⁾-based nonlinear polarization interferometer is proposed. It allows cross polarized wave generation with enhanced efficiency and obtaining different beam shapes of the generated cross-polarized wave. The interferometer consists of two polarizers, two quarter-wave plates and a BaF₂ crystal. The experiment with this interferometer confirms the predicted dependences.

We consider the femtosecond phase-matched noncollinear second-harmonic generation (SHG) in Strontium Barium Niobate (SBN) crystals with random ferroelectnc domains. We study both planar and radial second-harmonic (SH) radiation for the average input power P_f up to 600 mW. We show that the effect of thermal self-focusing of the fundamental wave occurring at P_f > 250 mW results in novel effects including the spatial localization of SHG, a change of the SH efficiency slope, and significant spectral broadening of both fundamental and SH beams

We applied the method of the amplitude envelopes to investigate fsec optical pulses in air and in vacuum and and obtain new linear amplitude equations governing their propagation. The obtained amplitude equations for media with week dispersion as air and the amplitude equations in vacuum are equal with precision-propagation constants. The equations were solved, using the method of Fourier transforms. One unexpected new result is the relative stability of light bullets and light disks and the significant reduction of their diffraction enlargement in respect to conical Fresnel's diffraction. It is important to emphasize here the case of light disks, which turns out to be practically diffractionless over distances of more than hundred kilometers. When we investigate the propagation of optical pulses only with few optical periods in the frame of amplitude equations and in the frame of the wave equation, we obtain equal diffraction behavior for the amplitudes in both cases.

We shell investigate the propagation dynamics of optical pulses in media with non stationary optical and magnetic response. We derived a new amplitude integro-differential equation describing their propagation in transparency region of such media. The applied method of the slowly varying amplitude approximation to this equation reduces it to nonlinear Slowly Varying Equation of Amplitudes (SVEA) in second approximation of linear dispersion and in first approximation to the nonlinear dispersion (SVEA). It is important to point out, that the obtained SVEA in media with no stationary optical and magnetic response is similar to the SVEA equation with stationary magnetic response. The only difference is the expression for group velocity and dispersion parameters. Partially, in paramagnetic media near to magnetic resonances it is possible to reach group velocity higher than velocity of light in vacuum.

The paper deals with the theoretical investigation of nonlinear surface polariton excitation in the metal film, contacting with the nonlinear medium in one side and the linear medium in other side. We consider that the nonlinear surface polariton excitation occurs due to the light falling on the metal film from linear medium with the incident angle greater that the total internal reflection angle. The phenomena of photon blockade and optical bistability are predicted.

New stationary solutions were identified in a transmission system with fiber, SOA, and BF and in the presence of the offset of the filter peak frequency from the carrier pulse frequency. Of particular significance are those with the negative values of the net gain. The model describing dissipative solitons in the accelerating reference frame was modified with the term related to Henry factor and stationary solutions were identified.

By applying the Lie group reduction method a full symmetry classification of one parameter group invariant solutions of two coupled nonlinear Schrodinger equations is presented. The physical situations under consideration include propagation of two polarization modes in weak and strong birefringent fibers, propagation of two waves at different carrier wavelengths, and nonlinear directional couplers.

It is researched the influence of the phase fluctuations on the coherence properties of the laser's radiation at propagation of short pulses in the optical fibers at the anomalous dispersion region. Two different methods for studying of modulational instability are applied and compared -method based on the solving of the Nonlinear Schrödinger Equation (NLSE) with stochastic initial conditions and method for researching of the Four-Wave Mixing in the fibers. The results received by these two methods are compared to determine the applicability of each of them.

The data represent life time test of a CW diode running in pulsed regime. It is shown that the reliability of CW laser diode run with 10 times higher peak currents is enough for many applications, where high peak power, high repetition rate diodes are a better choice than DPSS lasers.

The solutions of vector Nonlinear Schrodinger Equation (NLSE) in fiber with nonlinear dispersion and nonlinear refractive index of the type of n₂ ∝ (x² + y²) are presented in the report. Exact analytical 3D+1 soliton solutions of NLSE are obtained in Cylindrical Coordinate System {0;&rgr;;&Jgr;;z} which axis OZ coincides with geometrical axis of the &rgr;² = x² + y² ≠ 0. In the case of (x² + y²) → 0 is solved corresponding linear equation. It has been found the connection point between exact analytical solutions of both types of equations - vector nonlinear Schrodinger and corresponding linear equations. The obtained analytical solutions of both types of equations in cylindrical coordinates are represented and in Cartesian coordinates. Following the results the main application of these 3D+1 solitons is in realizing of stable waveguide propagation of laser pulses with random intensities in nonlinear fibers.

Possibility of deriving of approximated solutions of the nonlinear Schrodinger equation (NSE) is presented, using the Bogol'ubov's method of small parameter. Following the restrictions of first-approximation solutions, we obtain the ordinary differential equations system, which describes the temporal dependence of amplitudes, velocities, positions and phases of weak-interacting solitons. We consider that the ε small parameter method facilitates the application into analysis, when comparing with the method of scattering inverse task. The Bogol'ubov's ε parameter method gives the possibility to obtain the NSE solutions even in high order approximations, as well. Thus, the accuracy of calculations increases when studying the evolution of the interaction of soliton-like pulses.

The second- and third-order nonlinear optical properties of Magnesium Sulfite Hexahydrate (MgSO₃.6H₂O) were studied by Second-Harmonic Generation (SHG) and Degenerate Four-Wave Mixing (DFWM). Nanosecond pumping by Nd:YAG laser having a variable reflection output coupler was used. The effective quadratic (&khgr;⁽²⁾) and cubic (&khgr;⁽³⁾) nonlinear susceptibility values are obtained at room temperature. The dispersion of the nonlinear optical susceptibility of MgSO₃.6H₂O is also discussed.

Efficient frequency-doubling systems with a specific geometry configuration are used in order to obtain ultraviolet (UV) cw coherent radiation for laser spectroscopy of exotic radionuclides in the 30 ⩽ &Zgr; ⩾ 58 region. The compensation of the walk-off angle and the use of external cavity for second harmonic generation give most noticeable doubler efficiency increase. Three frequency-conversion systems are proposed for laser spectroscopy of nuclei. Second harmonic efficiency of 18% is obtained. Perspectives of using the injection seeded nonlinear converters in laser spectroscopy are also discussed.

We present experimental results for an investigation of both parametric and Raman scattering processes simultaneously occurring in optical fibers. The generation of Stokes as well as of anti-Stokes components under the influence of the parametric effects, is considered. The generated new optical frequencies can yield more favorable conditions concerning the material dispersion and the losses in fibers. Substantially nonlinear regime of interaction with a mutual exchange between the excited radiation and the generated signal frequencies is analyzed by solving the full system of equations with account of the real and imaginary parts of the nonlinear optical susceptibility.

Perturbed version of the complex Toda chain (CTC) has been employed to describe adiabatic interactions of N-soliton train of the nonlinear Schroedinger equation (NLS). Perturbations induced by weak quadratic and periodic external potentials are studied by both analytical and numerical means. It is found that the perturbed CTC adequately models the N-soliton train dynamics for both types of potentials. As an application of the developed theory we consider the dynamics of a train of matter-wave solitons confined to a parabolic trap and optical lattice, as well as tilted periodic potentials. In the last case we demonstrate that there exist critical values of the strength of the linear potential for which one or more localized states can be extracted from the soliton train. An analytical expression for these critical strengths for expulsion is also derived.

A three-component nonlinear Schrodinger-type model which describes spinor Bose-Einstein condensates is studied. These types of χ³-interactions are integrable by the inverse scattering method. We analyze its Hamiltonian properties and outline an algebraic procedure to derive their three types of soliton solutions based on Zakharov-Shabat dressing method. Their applications to spinor model of Bose-Einstein condensates are discussed.

We present a novel experimental technique for retrieving the spatial profile of a nonlocal response function in a medium with thermal nonlinearity. Our method is based on the quantitative measurement of the light-induced nonlinear phase distribution by holographic interferometry combined with an iterative process of two-dimensional deconvolution using the known pump beam intensity distribution.

Novel exactly integrable models and their exact analystic solutions found in this work to the problem of optimal solitons amplification demonstrate that the ideal amplification of the optical soliton is really possible if the dispersion and nonlinear properties of the nonconservative amplifying system are specially controlled in the experiments.

Laser-induced fluorescence (LIF) is emitted from leaf pigments irradiated with laser. LIF contains lots of information on living plants, so LIF spectroscopy, also known as the LIF technique, is a powerful tool for plant investigation. This paper mainly describes 1) the information that is obtained by plant LIF experiments with a focus on plant physiological information, and 2) practical field applications of the LIF technique, especially to agriculture and forestry, together with a detailed description of equipment systems. Through several experimental results, the usefulness of the LIF technique is discussed as a field monitoring technique for plant investigations. Finally, the concepts of a "general hospital for plant diagnosis" and "optical farming for the agricultural industry" based on LIF information are proposed.

At NOAA's Earth System Research Laboratory, lidar systems have been developed and applied to environmental probing for more than three decades. Progressing from early investigations of atmospheric turbidity and winds employing ruby and CO₂ lasers, current work is focused on the application of sensors to measure atmospheric properties important for improving air quality understanding and forecasting, and quantifying important climate forcing mechanisms. Additionally, lidar systems are being used for probing the ocean to observe fish schools and marine mammals for research on estuarine health. Here we briefly describe development and applications of lidar systems for characterizing winds and turbulence in the atmosphere, distribution and transport of ozone and aerosol concentrations in urban areas, and inventory of fish stocks in coastal water.

The present knowledge of the aerosol distribution is far from sufficient to properly estimate the role of aerosols in changes of the global and regional environmental conditions and climate. The information on the vertical distribution is particularly lacking and lidar remote sensing is the most appropriate tool to close this observational gap. EARLINET-ASOS, starting on the European Aerosol Research Lidar Network (EARLINET) infrastructure, consisting of 24 lidar stations distributed over Europe, will contribute to the improvement of continuing observations and methodological developments that are urgently needed to provide the multi-year continental scale data set necessary to assess the impact of aerosols on the European and global environment and to support future satellite missions.

In this work the results of an experimental assessment of the operation accuracy of three lidar systems in Sofia City are presented. The investigation was carried out performing an inter-comparison of profiles of the atmospheric aerosol backscattering coefficient simultaneously measured by the lidars. All three lidar systems are involved in regular measurements within the frame of the EARLINET-ASOS (European Aerosol Research Lidar Network: Advanced Sustainable Observation System) European project. Twenty-four lidar stations, distributed over 16 countries in Europe are associated in this network. The main objective of the project is the establishment of a large statistical database of the aerosol distribution on the European scale. In order for the data to be reliable, preliminary tests of the quality of work of the individual lidar systems should be performed. That was the reason to perform the present study. The experiments on simultaneous operation of the lidar systems were carried out according to the fixed EARLINET-ASOS schedule starting in April 2006. The mean difference in the aerosol backscatter for all profiles obtained simultaneously and the standard deviation of the differences were calculated and compared.

The efficiency is studied of some applications of a recently developed lidar-type gamma-ray tomography approach for non-destructive evaluation of dense media. The approach consists in time-to-range resolved detection of the Compton returns from the probed object (irradiated by annihilation gamma-photon sensing beams) and data processing based on a lidar-type equation and intended for determination of the extinction and backscattering profiles along the line of sight. The concrete purpose of the work is to reveal by statistical modeling the capabilities, under Poisson noise conditions, of investigating underground layers and detecting low-contrast ingredients such as plastic landmines in soil. The results from simulations show that the method is capable of finding and identifying down to 5 % density-contrast ingredients in soil, at depths to 20 cm, with spatial resolution of 1 to 10 mm, for measurement time of 10 to 1000 s and activity of the gamma-ray source of 50 - 300 mCi. So, the method could be successfully used for examination of ground for landmines.

Some results obtained during two campaigns (summer 2004 and autumn 2005) of observation of the planetary boundary layer dynamics over the urban area of the Sofia city are presented. An EARLINET scanning aerosol lidar, an ozone analyzer and a ground meteorological station were used during the observations. Particularly, the mixing layer development and the residual layer destruction along with the relevant ground level ozone concentration variation followed during the convective boundary layer formation in two situations (in the case of a partial solar eclipse, and in the case of atmospheric internal gravity waves presence) are presented and considered.

Four campaigns of investigation of the atmosphere over the urban area of the Sofia city were carried out. An EARLINET scanning aerosol lidar, a spectrometer and a ground meteorological station were used during the observations. Multiple aerosol layers of variable thickness (200 600 m) were systematically observed in the planetary boundary layer over the area. A study of various optical characteristics of the atmospheric aerosol such as extinction coefficient, aerosol optical depth, Angstrom parameters (&agr; and &bgr;), etc. is performed and their variations are followed during the convective boundary layer formation.

We report on application of a distributed feedback (DFB) quantum cascade laser (QCL) for open path spectroscopic monitoring of ozone, water vapor, CO₂ and air temperature. The thermal chirp during a 400 ns long laser pulse at repetition rate of 1 kHz is used for fast wavelength scanning of two water vapor absorption lines, few O₃ lines and a CO₂ line, centered at 1032 cm^-1. A tuning range of 1.7 cm^-1 is achieved. The fast wavelength scanning of the QCL has the advantage of not being affected by atmospheric turbulence, which is essential for long open path measurements. A direct absorption method was adopted in the measurements. Monostatic experimental setup, consisting of a QCL, a retroreflector and a detector is employed. The lowest detection limit for ozone is about 0.2 ppb at 6 km open path. The relative humidity measurements sensitivity depends on the temperature and at 293 K is about 1%. The resolution of the temperature measurements is better than 0.5 K. The column densities and temperature retrieved from the transmittance spectra are obtained, performing averaging of 10 seconds, which is much shorter, compare to other open path techniques.

We have demonstrated a possibility for a spatial resolved open path spectroscopy using pulsed quantum cascade laser (QCL). Using a pulsed light source, as a QCL, and a few retroreflectors placed at different distances, allows splitting the distance of interest to a few parts. Each retroreflector reflects a fraction of the energy back and reflected signals reach the detector with different delays. Using the retroreflectors with increasing sizes allows keeping the amplitudes of the received signals almost constant, independently of the distance. The spatial resolution &Dgr;l is proportional to the pulse length &Dgr;t and is given from the same equation used in LIDAR techniques. The thermal chirp during the relatively long laser pulse is used for fast wavelength scanning. The latter has the advantage of not being affected by atmospheric turbulence, which is essential for long open path measurements. 200 ns pulse duration was used to achieve a 30 m spatial resolution. The latter is even better than urban areas mesoscale modeling requires. At the same time, the tuning range is about 0.8 cm^-1, which is sufficient to scan one or even several absorption lines at normal atmospheric pressure.

Statistical image processing methods are widely used for analyzing various random processes. One of these methods is the correlation method, which is applicable in the remote sensing for measuring the transport velocity of aerosol fields and determination of their statistical characteristics such as averaged lifetime, size, orientation, etc. In this work, an image data processing technique based on the temporary instabilities method is described, enabling velocity measurements of statistically homogeneous objects. The ability of the proposed technique for accomplishing simultaneous velocity measurements of different inhomogeneities is demonstrated experimentally. The main drift velocity vector is set by the position of the global correlation maximum, wich is obtained for different couples of recorded images.

A radiometric instrumentation was constructed and utilized to measure the hemispherical radiation reflected by the observed object being irradiated by a parallel infrared beam. The results of initial laboratory investigation of spectral hemispherical emissivity of limestone and hematite samples are reported. The reported measurements have been performed with spectral resolution of about 0.2 &mgr;m in the thermal infrared (TIR) band (8-14 &mgr;m).

Despite the fact that the laser applications in human ophthalmology are well established, further research is still required, for better and predictable ablation dosimetry on both cornea tissue and intraocular lenses. Further studies for alternative laser sources to the well established excimer lasers, such as UV or mid-infrared solid state lasers, have been proposed for refractive surgery. The precise lens ablation requires the use of laser wavelengths possessing a small optical penetration depth in the cornea and in the synthetic lenses, in order to confine the laser energy deposition to a small volume. In order to eliminate some very well known problems concerning the reshaping of cornea and the modification of the optical properties of the intraocular lenses, ablation experiments of ex vivo porcine cornea, acrylic PMMA and hydrophilic lenses were conducted with an Er:YAG laser (2.94 &mgr;m) and the fifth harmonic of a Nd:YAG laser (213 nm). The morphology of cornea was recorded using a cornea topography system before and immediately after the ablation. Histology analysis of the specimens was obtained, in order to examine the microscopic appearance of the ablated craters and the existence of any thermal damage caused by the mid-infrared and UV laser irradiation. The macroscopic morphology of the intraocular lens craters was inspected with an optical transmission microscope. Measurements of the ablation rates of the lenses were performed and simulated by a mathematical model.

Concentration of oxygen in tissue plays an important role in enhancing in vivo wide variety of biochemical reactions including cell metabolism. Aerobic cell metabolism is primary mechanism in energy production in tissue. Controlling this mechanism gives unique possibility of biological stimulation to reach therapeutic effect. This goal could be reached by laser-induced photodissociation of oxyhemoglobin in cutaneous blood vessels. This phenomenon is considered as a main mechanism of biostimulating and therapeutic effect of low energy laser radiation. Laser-induced photodissociation of oxyhemoglobin in vivo manifests itself through the changes of the value of arterial blood saturation before and during the laser irradiation. High sensitive pulse oxymeter could be used for the measurements of the level of arterial blood saturation. Unique possibility is reached in local increase the concentration of oxygen by additional releasing it into tissue. Laser-induced enrichment of tissue oxygenation stimulates of cell metabolism and allows develop new effective methods for laser therapy as well as phototherapy of pathologies where elimination of local tissue hypoxia is critical.

In this study are presented some initial results using LEDs as excitation sources for the needs of fluorescence spectroscopy of the skin, which are compared with the results obtained by nitrogen laser used as excitation source for cutaneous fluorescence. The main studies are made by developed in IE-BAS experimental fibro-optic system for fluorescence spectroscopy. Several volunteers, representative of each skin phototype typical for Bulgarian region, namely--phototypes I, II and III were investigated by the methods of fluorescence spectroscopy of the human skin on several anatomic sites, typical for this type of measurements--palm, medial part of the forearm and lateral part of the forearm. Fluorescence maxima detected are addressed to the typical fluorophores existing in the cutaneous tissues. Influence of main skin absorbers, namely melanin and hemoglobin, is also discussed and their impact on the fluorescence signals received from different anatomical areas and skin phototypes is determined.

The phthalocyanine zinc(II) and aluminum (III) complexes were studied to photoinactivate the bacterial strains, Staphylococcus aureus, methacillin-sensitive and methacillin-resistant, Pseudomonas aeruginosa and one yeast Candida albicans. The binding of phthalocyanines to bacteria and fungi cells was evaluated by the means of laserinduced fluorescence technique. The fluorescent spectra of dyes (650 - 800 nm) after direct excitation (635 nm) were measured as follows: 1. for the aqua supernatants obtained after 10 min cell incubation with the respected phthalocyanines (1.6 &mgr;mol.l^-1), 2. for the washed from the unbound dye cells, and 3. for the organic extracts from the three times washed cells. Fluorescent intensities at the emission maximum (~690 nm) were compared to the spectra of the phthalocyanines in organic solutions. The phthalocyanines uptake data for bacteria and fungi were determined at different cell densities. Nevertheless the better fluorescence properties of AlPc (fluorescent quantum yield of 0.4 towards 0.3 for ZnPcs) the lower drug accumulation in microorganisms was obtained. PDI results indicated an intensive lowering of the bacterial survival of both strains of S. aureus treated with cationic ZnPcMe followed by the anionic ZnPcS, at irradiance of 100 mW cm^-2 and fluence rate of 60 J cm^-2. More resistant to phototreatment P. aeruginosa and morphologically complicated yeast C. albicans were successfully inactivated only with cationic ZnPcMe. These data indicate the promising future application of cationic phthalocyanine in photodynamic inactivation of pathogenic microorganisms.

Photodynamic therapy (PDT) utilizes a combination of sensitizer, visible light and molecular oxygen to generate singlet oxygen and reactive oxygen species (ROS) such as hydrogen peroxide, hydroxyl radical and superoxid anion. Photochemical reactions lead to damage and destruction of cancer cells. The most suitable and effective source of radiation used in PDT is a laser. For this study, a semiconductor laser with output power of 50 mW and 675 nm was selected. In this paper we report a generation of ROS using chloroaluminium disulphonated phthalocyanine (ClAlPcS₂) in A549 bronchogenic carcinoma cell line after PDT in vitro. Phthalocyanines, belonging to a new generation of substances for PDT, exhibit effective tissue penetration because of their proper light absorption region, chemical stability and photodynamic stability. The fluorescence measurement with molecular probes, CM-H₂DCFDA and Amplex Red, was performed for detection of ROS generation and hydrogen peroxide release from cells. Our results demonstrated, that irradiation of cells by laser dose of 10 J.cm^-2 induces higher rates of fluorescence in cells loaded with phthalocyanine compared to 20 J.cm^-2. Furthermore, the production of ROS increases up to sensitizer concentration of 10 &mgr;M. The highest ROS generation was observed at laser dose of 10 J.cm^-2 and 10 &mgr;M ClAlPcS₂. The rates of fluorescence for hydrogen peroxid measurements were almost identical with all chosen concentrations at laser doses of 10 and 20 J.cm^-2.

In order to elucidate the molecular mechanism of the non-photochemical quenching of the excess light energy – quenching of excited chlorophyll a singlet states, low-temperature (77 K) steady-state laser fluorescence emission spectroscopy was applied to the main chlorophyll a/b protein light harvesting complex of photosystem II in different aggregation states. The aggregation of the complexes led to the quenching of the chlorophyll a fluorescence, as in the process of non-photochemical quenching. The quenching is concomitant with a strong broadening of the emission spectra and an appearance of a new emission band red shifted compared to the emission spectrum of the trimeric forms of the light harvesting complex of photosystem II. The aggregation state of the complexes was varied by changing the concentrations of the used detergent n-dodecyl &bgr;-D-maltoside. The low-temperature chlorophyll a emission spectra of the light harvesting complex of photosystem II were excited by laser line at 488 nm of an argon laser. Spectra were decomposed into the bands attributed to the trimeric and aggregated forms of the light harvesting complex of photosystem II. Based on the analysis of the obtained data and the new structure of light harvesting complex of photosystem II, a model describing quantitatively the quenching of the chlorophyll a fluorescence in the light harvesting complex of photosystem II in different aggregation states is proposed. The model revealed that upon aggregation besides the changes in the relative absorption of small and large aggregates, the amount of quenchers, most probably chl a dimers, and the rate constant for energy transfer to them are also changed.

We report new results on the light enhanced teeth whitening obtained in a research collaboration financed by the Medical Science Council of the Medical University of Sofia. The project is an extension of previous research and its basic goal is to develop new teeth bleaching substances and procedures, in which the activators are diode lamps (LED).

The main goal of this study is to investigate the treatment effect of combined therapy over Keratitis Herpetica Dendritica applying drugs Pandavir and Acycovir in combination with He-Ne laser irradiation. The current survey includes 75 patients with Keratitis Herpetica Dendritica that are divided in three groups. The first group of 25 patients is treated with Acycovir. The second group, which includes 24 patients, is treated with Pandavir and Acycovir. In the third group that consists from 26 patients, besides the abovementioned combination of drugs is applied low-level laser therapy using He-Ne laser, emitted at 632,8 nm wavelength, with power density 0,3 mW/cm² and light exposure used - 3 minutes. The flourescein reaction was monitored every day to detect the eye recovery. We observe earliest answer reaction to the treatment applied in the group of He-Ne laser& Pandavir&Acycovir, revealing as inflammation suppression and perifocal edema disappearance in the group treated. Eyes treated only with Acycovir present mean time of improvement (MTI), as the flourescein colorization disappearance and epithelization setting in for 9,3±1,2 days is observed. Similar results were obtained on the eyes treated in double combination, Pandavir and Acycovir, with MTI - 8,2±1,1 days. The best effect was obtained by the triple combination: Pandavir, Acycovir and He-Ne laser (statistically proved), with the mean time of improvement 6,2±1,3 days. The combined laser treatment shows significant additional effect on the recovery rate. The combined treatment with He-Ne laser, Pandavir and Acycovir is revealed as an efficient method for eye therapy of Keratitis Herpetica Dendritica.

In current study oral cavity hard tissues autofluorescence was investigated to obtain more complete picture of their optical properties. As an excitation source nitrogen laser with parameters - 337,1 nm, 14 &mgr;J, 10 Hz (ILGI-503, Russia) was used. In vitro spectra from enamel, dentine, cartilage, spongiosa and cortical part of the periodontal bones were registered using a fiber-optic microspectrometer (PC2000, "Ocean Optics" Inc., USA). Gingival fluorescence was also obtained for comparison of its spectral properties with that of hard oral tissues. Samples are characterized with significant differences of fluorescence properties one to another. It is clearly observed signal from different collagen types and collagen-cross links with maxima at 385, 430 and 480-490 nm. In dentine are observed only two maxima at 440 and 480 nm, related also to collagen structures. In samples of gingival and spongiosa were observed traces of hemoglobin - by its re-absorption at 545 and 575 nm, which distort the fluorescence spectra detected from these anatomic sites. Results, obtained in this study are foreseen to be used for development of algorithms for diagnosis and differentiation of teeth lesions and other problems of oral cavity hard tissues as periodontitis and gingivitis.

The majority of previous femtosecond laser ionization studies have been carried out on atomic, diatomic or small polyatomic molecules. The understanding of interaction of intense laser pulses with polyatomic molecules is at a preliminary stage. It was difficult to examine the behavior of more complex molecules in the presence of intensive laser field due to their involatility and thermal lability. In the ionization experiments performed in the current research the polyatomic molecules irradiated with ≈ 30 fs laser pulses, at wavelength 800nm do not exhibit an extensive fragmentation, and produce multiply charged ions in the intensity range of 10¹⁴W/cm². Studies of ionization mechanisms in the case of femtosecond ionization have revealed that the dissociation paths can be avoided. To establish an intact ionization of molecules two regimes of photodissociation can be distinguished: absorption-dissociationionization (ADI) and absorption-ionization-dissociation (AID) regime. It was discovered that the crucial parameter for the post-ionization experiments is the energy necessary for ionization of the neutral species. The ionization efficiency depends strongly from the precise timing of the laser pulses and from the geometrical overlap of the focus of the postionizing laser beam with the emitted particle cloud.

In the recent study delta-aminolevulinic acid/Protoporphyrin IX (&dgr;-ALA/PpIX) is used as fluorescent marker for dysplasia and tumor detection in esophagus and stomach. The &dgr;-ALA is administered per os six hours before measurements at dose 20mg/kg weight. High-power light-emitting diode at 405 nm is used as an excitation source. Special opto-mechanical device is built to use the light guide of standard video-endoscopic system (Olimpus Corp.). Through endoscopic instrumental channel a fiber is applied to return information about fluorescence to microspectrometer (USB4000, OceanOptics Inc.). The fluorescence detected from tumor sites has very complex spectral origins. It consists of autofluorescence, fluorescence from exogenous fluorophores and re-absorption from the chromophores accumulated in the tissue investigated. Mucosa autofluorescence lies at 450-600 nm region. The fluorescence of PpIX is clearly pronounced at the 630-710 nm region. Deep minima in the tumor fluorescence signals are observed in the region 540-575 nm, related to hemoglobin re-absorption. Such high hemoglobin content is an indication of the tumors neovascularisation and it is clearly pronounced in all dysplastic and tumor sites investigated. The lack of fluorescence peaks in the red spectral area for normal mucosa is an indication for selective accumulation of &dgr;-ALA/PpIX only in abnormal sites and gives high contrast when lesion borders are determined from clinicians during video observation in the process of diagnostic procedure. Very good correlation between fluorescence signals and histology examination results of the lesions investigated is achieved.

The potentialities are investigated of a single-sided optical tomography approach based on lidar principle. Concretely, the informative depth of sensing is estimated that outlines the underside area in the probed object where one could reveal inhomogeneities with some desirable contrast. The sensing radiation is supposed to consist of picosecond laser pulses with pulse repetition rate of ~ 10 MHz and optimum wavelength of 800 nm. The maximum permissible skin exposure is considered as determinant. The longitudinal and the transversal resolution intervals are chosen to be 2 mm and 3 mm (or 1 cm), respectively. It is shown that, under the above described conditions, inhomogeneities with contrast 1-10 % would be detected at depths of 1 to 4 cm, depending mainly on the values of the attenuation coefficient chosen here to vary correspondingly from 1.4 mm^-1 to 0.4 mm^-1.

The goal of anticancer therapy is achievement of balance between destruction of tumour cells and tissues and conservation of physiological functions of noncancer cells. Photodynamic therapy (PDT) is one of novel alternative treatment modality of malignant neoplasms. This method is based on cytotoxic action of excited sensitizers in the oxygen-rich environment. Sensitizers bound to cells and are excited by light source identical to absorption maximum of sensitizer. Photodynamic reactions lead to production of reactive oxygen species (ROS), which cause necrosis or apoptosis of cancer cells. The objective of our work was to analyse of phototoxicity in the sense of DNA damage in cancer cells after PDT by single cell gell electrophoresis (SCGE, comet assay) using ZnTPPS4 (zinc(II)-5,10,15,20-tetrakis(4-sulphonatophenyl) porphyrine and disulfonated chloraluminium phthalocyanine ClAlPcS₂ as sensitizers. Violet light emitting diodes (LEDs; 1.5 mJ.cm^-2.s^-1; 418 nm) and semiconductor laser (50mW; 675 nm) were used as sources of radiation. Level of DNA fragmentation was detected after application of different light doses.

Optical spectroscopy and in particular laser-induced autofluorescence spectroscopy (LIAFS) and diffuse reflectance spectroscopy (DRS), provide excellent possibilities for real-time, noninvasive diagnosis of different skin tissue pathologies. However, the introduction of optical spectroscopy in routine medical practice demands a statistically important data collection, independent from the laser sources and detectors used. The scientists collect databases either from patients, in vivo, or they study different animal models to obtain objective information for the optical properties of various types of normal and diseased tissue. In the present work, the optical properties (fluorescence and reflectance) of two animal skin models are investigated. The aim of using animal models in optical spectroscopy investigations is to examine the statistics of the light induced effects firstly on animals, before any extrapolation effort to humans. A nitrogen laser (&lgr;=337.1 nm) was used as an excitation source for the autofluorescence measurements, while a tungsten-halogen lamp was used for the reflectance measurements. Samples of chicken and pig skin were measured in vitro and were compared with results obtained from measurements of normal human skin in vivo. The specific features of the measured reflectance and fluorescence spectra are discussed, while the limits of data extrapolation for each skin type are also depicted.

A new method of laser-induced tissue oxygenation for elimination of tissue hypoxia and increase in the efficiency of the method of Photodynamic Therapy (PDT) is proposed. It is shown that significant increase in the efficiency of PDT due to extra supply of cancer tissue by free oxygen could be reached.

The photosynthetic antenna systems are able to regulate the light energy harvesting under different light conditions by dynamic changes in their protein structure protecting the reaction center complexes. The changes modulate the electronic structure of the main antenna pigments (chlorophylls and carotenoids) and distort the characteristic planar structure of carotenoids, allowing their forbidden out of plane vibrations. Electronic absorption and low-temperature resonance Raman spectroscopy were used to study the changes in composition and spectral properties of the major carotenoids in spinach Photosystem I particles due to high light treatment. The duration of the applied intensity of the white light (1800 &mgr;E m^-2 s^-1) was 30, 60 and 120 minutes. We used Raman scattering in an attempt to recognize the type and conformation of photobleached carotenoid molecules. The resonance Raman spectra were measured at 488 and 514.5 nm, coinciding with the absorption maximum positions of the carotenoids neoxanthin and lutein, correspondingly. The results revealed nearly a full photobleaching of the long wavelength lutein molecules, whereas the bleaching of neoxantin molecules is negligible. The involvement of these changes in the photoprotection and photoinactivation of the Photosystem I particles was discussed.