Optical reference frequencies are provided by lasers of which the frequencies are stabilized to suitable absorption lines. Presently, twelve reference frequencies/wavelengths within the wavelengths range from 243 nm to 10.3 micrometers are recommended by the International Committee of Weights and Measures as references for the realization of the meter and scientific applications. As typical examples, we describe a diode-pumped, frequency doubled YAG-laser stabilized to an absorption line of molecular iodine and a Ca-stabilized laser. The latter one has been developed in two versions, a transportable system utilizing a small beam of thermal Ca atoms and a stationary standard based on laser cooled and trapped Ca atoms. The frequency of the Ca standard based on cold Ca atoms has been measured by a frequency chain allowing a phase-coherent comparison against the primary standard of time and frequency, the caesium clock. Its value is v_Ca equals 455 986 240 494.13 kHz with a relative standard uncertainty of 2.5 (DOT) 10^-13.

We model the transport of light through the atmosphere including polarization and change of wavelength as an iterated sequence of collisions, changes of wavelength, directional scatterings, and changes of the state of polarization. The collision probabilities are determined by the extinction coefficient, the change of wavelength by the relation of the collision intensities of the different `components' of the scattering medium, and the directional scattering distributions by the polarized phase function which is obtained from scattering intensities. These scattering intensities depend on the ensembles of scattering particles, the wavelength, and the polarization. We obtain them from the Mueller matrices determining the single scattering event. For easier simulation of the directional scattering the polarized phase function, which is a probability density on the unit sphere of the 3D Euclidean space, is disintegrated into the conditional polarized phase function (characterizing the azimuthal direction of scattering) and the (ordinary) phase function (characterizing the zenithal off axis direction of scattering). We characterize the path of a photon of this corpuscular stochastic process of multiple scattering by a sequence of tupels each describing the point of collision, the wavelength after collision, the direction of scattering, and the state of polarization after scattering. Starting from this model we derive exact multiple scattering lidar equations including polarization and change of wavelength. Step by step we derive from these lidar equations more specific ones: first an exact multiple scattering lidar equation with polarization (and without change of wavelength), then a multiple scattering lidar equation without polarization for collections of particles with a scattering distribution which is rotational invariant with respect to the incident beam.

The Next Generation Space Telescope is currently envisioned as an eight meter diameter cryogenic deployable telescope that will operate at the earth sun libration point L2. A number of different designs are being examined within NASA and under industry studies by Ball Aerospace, Lockheed- Martin and TRW. Although these designs differ in many respects, they all require significant advancements in the state-of-the-art with respect to large diameter, ultra- lightweight, mirrors. The purpose of this paper is to provide insight into the current status of the mirror development program.

In this paper laser applications to fluid dynamical problems are presented. Firstly as for the recent research on cavitations, pulsed-laser-induced cavitation bubble in liquid nitrogen is studied. The bubble is produced by focused and pulsed irradiation of second harmonics of YAG laser in the cryostat. The dynamics of laser-induced bubble is visualized by high-speed shadowgraphs and schlieren photographs by an image-converter camera (Imacon-790). Bubble and solid wall interactions are also investigated. Based on the results obtained, a novel laser surface processing technology using the pulse-laser-induced cavitation bubbles is secondly proposed. The possibility of cold material surface processing by produced cavitation bubble is discussed including the cryogenic range. Furthermore, discussing by the fundamental results of the experiment of laser-gas molecular absorption, the possibility of decomposition of environmental gases by strong CW CO₂ laser irradiation is also studied. Freon 12, 113, and other environmental gases including SF₆ are very tough to be decomposed, and they break effectively the ozone molecules at high altitude above the Earth, or they heat up the earth. The wavelength range of the infrared laser is suitable for the molecular absorption to increase their temperature to be ionized. The possibility and trial experiments are discussed.

Shock waves, which are generated by pulsed discharges in excimer lasers, cause a complicated time history of density of laser medium, and successively causing arcing and non- homogeneous excitation in the laser cavity. To clarify the characteristics of the generation and propagation of shock waves by these strong pulse-discharges in an excimer laser, experimental study and numerical analysis using a TVD scheme and Grid-distortion Splitting Method have been carried out. The shock waves are visualized using a CCD color schlieren technique. Numerical calculation by Yee's symmetric TVD scheme is performed for the conditions that corresponds to the experiments. The initial conditions of our calculations are determined by measured results by the laser schlieren method, and from schlieren photographs. The propagation and attenuation of the shock waves in our experimental operation are also visualized from the numerical results and compared to the experimental results.

Laser beam welding of aluminum alloys is becoming of increasing interest with respect to light-weight structures. Compared to welding of steel, the process is rendered difficult by the specific material properties. On the basis of a fundamental understanding of the relevant physical mechanisms, guidelines for a successful conduction of the welding process and quality assurance are presented. Factors relevant for deep penetration threshold, process efficiency, process stability and for achieving high seam quality are discussed. In particular, by the combination of two individual focal spots along or normal to the welding direction a process-adapted distribution of the laser power yields substantial improvements. With respect to quality assurance a new method presented here uses the relationship between the geometry of the keyhole and the emitted laser light to control welding depth and to monitor seam defects.

The basic interaction mechanism of pulsed laser ablation of tissue reveals a complexity of parameters, such as the optical properties of the tissue and the technical characteristics of the laser beam. The role of the laser wavelength, the pulse duration, the energy fluence, etc. as well as the implications on the beam delivery means, the ablated surface modifications and the diagnostic techniques employed are under investigation. For example, it was experimentally verified that when using mid-infrared lasers with pulse durations in the ns range, the photothermal mechanism involved exhibits strong absorption restricting the residual thermal damage to a relatively small zone. On the other hand the ablation of tissue with ultrashort, picosecond and femtosecond, visible and near-infrared laser pulses has been investigated as an alternative, as the energy threshold for ablation biological tissue, depends approximately on the square root of the pulse duration. However the pulse length shortening creates problems to the fibers or the waveguides ends, due to the very high laser power densities involved. Conventional and advanced microscopy, scanning electron microscopy--SEM and atomic force microscopy--AFM, were used to study the surface and ends alterations of the delivery system involved and the surface alterations of the soft or the hard tissue target in pulsed laser ablation. Finally differentiation between the normal and the pathological tissue was achieved by employing the laser induced fluorescence--LIF diagnostic technique in a long term effort to develop a computer aided system, which will facilitate the automated, real-time characterization of healthy or atherosclerotic plaques in a less invasive laser ablation clinical procedure.

The experimental results on deposition of superconducting, semiconducting, quantum size and magnetic films by pulsed laser deposition technique are presented. The possible applications of pulsed laser deposition technique are discussed.

Contribution deal with laser deposition of superhard carbon nitride (beta) -C₃N₄ thin films. Survey of results reached by various groups is done. Problems of stoichiometry definition, stoichiometry measurement and deposition parameters having influence on the increase of nitrogen content in layers is discussed.

The design and development of a compact, low cost, subsonic cw HF chemical laser with expected output power of the order of approximately 100 mWatts that requires less than 5 lt/s pumping capacity is presented. A theoretical estimation of the minimum pumping capacity required in order to obtain an output power of 100 mWatts is given. The laser operates with a He/SF₆/H₂/O₂ gas mixture at an overall pressure of 4 - 8 mbar. A dc electric discharge is used for the SF₆ dissociation. In order to operate at such low gas flow rates the mixing channel dimensions were reduced down to a cross section of 0.2 cm height by 13 cm width. Hydrogen is transversely injected into the flow through approximately 285 holes of 0.03 cm diameter. This low cost compact laser system is suitable for a wide range of experimental requiring mid-infrared cw laser radiation such as laser-tissue interactions and environmental studies.

The results of a numerical, diffraction type, analysis performed for a multipass stable resonator designed for a 2.5 kW transverse-flow CO₂ developed in IFFM for industrial applications are discussed in the paper. The mode beam properties, output power, misalignment sensitivity, and the output beam focusing conditions are studied for various geometrical configurations of an optical cavity designed for a laser and for different medium characteristics. As the result of the analysis the conditions for the laser operation at the required level of the output power has been specified.

A diagnostic scanning instrument developed in IFFM provides a view of the laser beam profiles and allows for the analysis of the factors influencing the beam quality. The method of measurements and their results concerning the 1.2 kW CO₂ industrial laser beam propagation characteristics are presented in the paper. The experimental power density distributions of focused and unfocused beams are analyzed. From the beam caustic recorded under focused conditions the principal propagation beam parameters were estimated and compared with those determined by the knife-edge method.

A laser cavity containing highly selective reflector based on a multipass grazing-incidence diffraction grating is described. The operation of the multipass selective reflector (MPSR) is demonstrated and studied experimentally in the case of pulsed dye laser pumped by frequency-doubled Nd:YAG laser. Numerical calculations concerning gain- switched Ti:Sapphire laser with MPSR are also done. An increasing of the spectrally pure output energy more than 5 times is achieved. Decrease of the threshold energy and broadening of the tuning range of several times are also observed depending on the pumping conditions. The calculations show that, in the case of gain-switched Ti:Sapphire laser pumped by Nd:YAG laser, the temporal characteristics of the radiation, the build-up time and the pulse duration are considerably shortened by using MPSR. The improved energy, spectral, and temporal parameters of tunable lasers with MPSR make them suitable for different applications (spectroscopy, biology, DIAL, etc.) as a separate sources or as a part of injection-seeding tunable laser systems.

A comparative experimental study of two versions of an injection-seeding laser system containing a slave laser (SL) with a ring-linear dual-channel competitive cavity and with a simple ring one is presented. The spectral purity of the SL output radiation and efficiency of the SL reverse wave suppression in dependence on the seeding conditions are investigated. It is shown that in the case of a dual-cavity competitive SL with a ring main channel both the spectral background and reverse radiation are fully suppressed. This is realized in a compact scheme without optical isolators and at any ratios between the SL energy and the seeding source one.

We report an original approach for tunable subnanosecond pulse (200 - 500 ps) generation in a ring dye laser. It is based on limitation of generation to a single `spike' from the starting transient process using for excitation a quasi- rectangular pulse with duration less or comparable with the time interval between the spikes. The pumping pulse (3 - 7 ns) is formed both by electrooptical division of a standard nanosecond (15 - 50 ns) pulse emitted by a Q-modulated laser in an original scheme and by overlapping of the obtained partial pulses which are fed bi-directionally into the active medium of the ring laser.

In this paper we report a comparative study the amplification and spectral tuning characteristics of an injection seeded Ti:Sapphire laser and multipass (4 passages) amplifiers. We show the advantages of injection seeding method to amplify input pulses of low energy levels (nJ and sub nJ). In the multi-passages amplifiers the wave competition for the two wavelength amplification is low. For high level (mJ) pulses the both systems are comparable, but in the injection locking amplifier the temporal pulse shape distortion is essentially high. The energy and power amplification levels are compared both with the change of the output width. For the reported two new multi-passages schemes we are study the dependence of the characteristics on the input polarization.

Combining optical asymmetry in reflection of a unequal mirrors interference wedge with its focusing property at negative incidence, we propose effective separation of a laser oscillator from a highly excited amplifier in a tunable laser oscillator-amplifier system, i.e. solution of the problem with removal of the background radiation self- injection.

We show, that the unbalanced bi-directional passive self- injection permits to obtain a pulsed unidirectional operation at the reference atomic absorption line in a ring Ar³⁺ pumped Ti³⁺:Al₂O₃ laser with a repetition rate of order of 10³ - 10⁵ Hz. The model used for the description of this type of laser is based on the adaptation of the rate equations systems. By computer simulation, the dependence for the repetition rate from the laser parameters and the switching time is obtained.

The quality of precise machining with a CuBr laser ((lambda) equals 510.6 nm, (lambda) equals 578.2 nm, power up to 120 W) depends on the laser beam quality determined by the laser beam divergence and intensity distribution in the cross section of the laser beam. The set-up presented in this report makes monitoring the laser beam intensity distribution (the laser beam profile) in the real time and recording it as a bitmap or binary files possible. Using this set-up the laser beam divergence and spot size of the focused laser beam can be also determined.

Brief overview of recent optimization studies of hollow cathode discharges, mainly the segmented hollow cathode arrangement for the excitation of metal ion lasers is given here. Results of parametric studies (on the 282.3 nm Au II and 780.8 nm Cu II transitions) including optimization of buffer gas composition, cathode-anode area ratio and inner diameter of the discharge tube are presented here together with some modeling results.

The Hydrogen influence on (Ne+ H₂) hollow cathode discharge plasma characteristics has been studied. The discharge voltage/current characteristics have been registered and the electron temperatures and concentrations have ben measured by using Langmuir's probe technique in both pure Ne and (Ne + H₂) hollow cathode discharges as a function of H₂ concentration. The Hydrogen negative ion concentration has been obtained by the laser photodetachment method. The results show that small (up to 10%) concentrations of H₂ to Ne hollow cathode plasma improve the plasma conductivity and decrease the electron temperature. Negative hydrogen ions occur in (Ne + H₂) hollow cathode discharge. Their density with (Ne + 10%H₂) discharge is 2 X 10⁸ cm^-3 and they should be taken into account for a description of the plasma studied.

Pulsed He-Zn hollow cathode laser is investigated. Simultaneous lasing on five visible Zn II (491.2 nm, 492.1 nm, 589.4 nm, 601.2 nm and 610.2 nm) and three infrared Zn II (747.9 nm, 758.8 nm and 775.8 nm) lines is obtained. Helical configuration of the cathode is used. The dependence of the laser output parameters on the excitation pulse: peak value, duration and repetition rate and He and Zn pressures is investigated. Optimal lasing is obtained at 6 - 9 A peak current, 5 - 8 Torr He pressure, 420 - 450 degree(s)C tube wall temperature and 13 microsecond(s) pulse duration. Stable operation and no change in the output power is observed by the variations of the excitation pulses repetition rate up to 1000 Hz. Laser gain values of more than 100%/m for the Zn II 758.8 nm line, 30%/m for the Zn II 492.4 nm line and 15%/m for the 491.2 nm line are achieved.

A theoretical study on a He-Zn laser operating on the Zn II 758.8 nm line in the negative glow plasma of a pulsed hollow cathode discharge at intermediate pressures is presented. A detailed kinetic model of the plasmochemical reactions and radiative processes determining the inversion population on the Zn II 5p ²P_3/2 - 5s ²S_1/2 transition (758.8 nm line) is developed. A system of 13 non-stationary differential equations for the plasma and laser parameters is solved. The time dependent behavior of the plasma and laser parameters (excited states populations, electron and ion densities and laser gain) are numerically calculated. The behavior of the plasma and laser parameters as a function of the discharge conditions is obtained. The results are in a good agreement with experimental data.

In this work we present a theoretical estimation for VUV superluminescent laser gain employing electron-impact excitation and Super-Koster-Cronig decay in Zn vapors. The stimulated emission is produced on the 3d⁸4s^{2 1}G₄ - 3d⁹4p ³D₃ 130.6 nm two-electron transition of ZnIII. We use the existing information on atomic constants available in the literature to estimate the current densities that will be necessary to observe a significant gain, comparable to that observed in an experiment using x-ray excitation, produced in laser induced plasma. Our estimations show that such values of the gain are obtainable by pulsed electron excitation with time longitude greater than 1 microsecond(s) and high but possible current densities of the order of 10 kA/cm².

The tilt of the pulse front caused by misalignment in stretcher-compressor devices which are used in chirped pulse amplification should be carefully considered in the design of femtosecond laser systems. We present a convenient procedure for online measurement and minimization of the tilt in a grating stretcher/compressor setup. In addition, we present a theoretical model for the autocorrelation signal in the presence of pulse front distortion. The influence of the pulse front tilt to the autocorrelation function is numerically simulated and compared with the case for pulses with fourth order chirp.

In this work we analyze the nonlinear evolution of mixed edge-screw phase dislocations and provide arguments on the existence of 1D dark spatial solitary waves of finite length in bulk Kerr nonlinear media. The characteristic phase gradients force the dark beam to steer in space. An all- optical switching scheme is proposed and critically evaluated with respect to stability and deflection control. Experimental results are reported on the decay of quasi-2D dark spatial solitons into finite-length 1D dark spatial solitons. The role of the saturation of the nonlinearity is discussed.

We present experimental results on different types of self- oscillations in thermo-optical bistable interference filters. We model them by taking into account the finite time for thermal response and eventual time delay in the thermo-optical feedback.

The polarization labeling spectroscopy technique is used to study the B¹II and C¹(Sigma) ⁺ states of the KLi and the 3¹(Pi) and 6¹(Sigma) ⁺ states of the NaK molecules. Accurate molecular constants are derived. The potential energy curves for the 3¹(Pi) and B¹(Pi) states are constructed almost to the dissociation limits. For the double minimum 6¹(Sigma) ⁺ state nearly the whole inner potential well is characterized. The results are compared with the predictions of recent theoretical calculations.

The laser induced fluorescence spectrum (LIF) of the LiYF₄:Ho³⁺ (YLF:Ho) single crystals, pumped by the molecular fluorine pulsed discharge molecular laser at 157.6 nm was obtained in the vacuum ultraviolet (VUV) and ultraviolet (UV) regions of the spectrum. The observed transitions originate from the levels and the edge of the 4f⁹5d electronic configuration and they are assigned to the 4f⁹5d yields 4f¹⁰ interconfigurational transitions. The LIF spectra can be explained provided that phonon trapping is taking place within the Stark components of the 4f⁹5d electronic configuration. The absorption spectrum of the crystal samples in the VUV was obtained as well. The electric crystal field splits all the levels of the 4f⁹5d mixed configuration. We observed five main transitions between the ground level ⁵I₈ of the 4f⁹ electronic configuration and the Stark components of the levels of the 4f⁹5d electronic configuration in the spectral range between 118 - 158 nm, and four weaker transitions in the spectral range from 158 - 186 nm.

A reliable algorithm for temperature estimation of cooled atoms is proposed and investigated by 2D-Monte-Carlo simulation for the ensemble of ¹³³Cs atoms provided time-of-flight (TOF) and spatial distributions of falling atoms are found in two planes below the atomic cloud using fluorescence or transmission measurements. We assume that the atoms, being normally distributed in space, are left to fall freely at a certain moment and we suppose that collisions between them do not cause substantial distortion of the ideal TOF-distribution.

Superposition of states in Rubidium vapor has been obtained by optical pumping with frequency modulated diode lasers. The resulting dark states have been studied as a function of the applied magnetic field and an interference effect has been evidenced by irradiating the vapor with two counterpropagating beams.

We present an experimental study of fine structure (fs)- mixing in the 5²D state of Rb, and details of construction and performance of an external cavity cw diode laser, developed to provide a light source at 778 nm for two-photon excitation of Rb(5²D). Cross section for the fs-mixing Rb(5²D_5/2) yields Rb(5²D_3/2) in collisions with the ground state Rb(5²S_1/2) atoms was found to be 5.8 +/- 1.9 (DOT) 10^-14 cm².

In this paper He(2¹ S, 2¹P)+M interaction processes are investigated. There are no experimental data in the literature about the quenching cross sections of He(2¹ S, 2¹P) states by collisions with atoms of Rare Earth Elements. In this paper we report the preliminary results of the quenching of He(2¹ S, 2¹P) excited states by Yb atoms. A time resolved method and pulse electron excitation is used in this experiment. A comparison of the theoretical results and the experimental data are made.

For intra-cavity high resolution spectroscopy of acetylene (C₂H₂), an extended cavity diode laser (ECDL) system emitting at 1.55 micrometers has been built using a 600 lines/mm diffraction grating mounted in Littrow configuration. In a single pass absorption cell the linear absorption of a number of rovibrational overtone transitions of C₂H₂ has been registered. An external FP cavity (finesse of 300, free spectral range FSR equals 520 MHz) was built and utilized for C₂H₂ intra-cavity spectroscopy as well as for ECDL frequency stabilization. The Pound-Drever-Hall technique was used to lock the diode laser frequency to the external cavity with the servo bandwidth of 50 kHz. The C₂H₂ intra-cavity linear absorption was recorded in transmission at a pressure of 1.3 Pa. By combining the reflected and transmitted signals the influence of residual frequency fluctuation of the ECDL with respect to the external cavity was reduced and the signal to noise ratio was improved to 34 dB for a single pass linear absorption of 0.2%.

Good signal-to-noise ratio optogalvanic effect has been obtained in two kinds of hollow cathode discharges (coil and segmented construction) using commercially available low cost and low power diode lasers emitting in the visible region of the spectrum. The OG profiles of Ne and He transitions, suitable for diode laser wavelength locking to absolute reference, have been studied. The amplitude and sign of the optogalvanic signal have been measured simultaneously with the absorption in dependence of the gas discharge parameters in order to find the conditions for optimum OGS. OGS was observed also at a wavelength of 667.28 nm, where no transition was found in the tables of spectral lines available.

We report the observation of magneto-galvanic resonances (MGR) in traditional galvanic detectors--Ne-Cu (`Narva' type) and Ne-As (Pye Unicam) hollow-cathode lamps (HCL). We carried out comparative investigations of the characteristics of the MGR and the laser-induced galvanic signals arising as a result of the irradiation of the HCL by different laser lines. We believe that the variation of the discharge conductivity is caused by the self-alignment of the 1s₅ Ne metastable state. We also discuss some of the possible mechanisms that may relate the self-alignment destruction to the discharge conductivity change.

Two methods for gas monitoring are created and discussed. The cause-effect relation between the gas pressure or purity and an anomalous optogalvanic response is developed. The methods are realized by the same scheme.

Investigations on a pulsed O₂ plasma under low pressure (1 - 10) mbar have been carried out. Microwave pulses (2.45 GHz) with a duration of (50 - 200) microsecond(s) and a repetition rate of (10 - 500) Hz are typical for the experiments. The electron density has been determined by means of an HCN laser interferometer. Detection of negative ions O^- has been performed using a photodetachment technique with a Nd:YAG laser. A kinetic model predicting the temporal behavior of the densities of oxygen atoms and molecules, metastable singlets O₂(a¹(Delta) , b¹(Sigma) ), negative ions O^-, positive ions O⁺₂, ozone, and the electron density has been developed. The experimental and theoretical data are fond to agree well.

The DOH system in H₂O and 2 M aqueous salt solutions of NaSCN and (CH₃)₄NCl has been studied by the fluctuation model of hydrogen bonding. A number of quantitative parameters, characterizing the hydrogen bond network of the DOH system has been derived. The salts have an influence on the structure of the solutions in accordance with their positions in the Hofmeister series. A simple and efficient procedure for evaluation of the thermodynamical parameters of water solutions is described and verified. The specific heat values C_V of the studied solutions are determined by means of the statistical integral Z(T). The values coincide very well with literature data.

Observations of the horizontal distribution of the aerosol extinction coefficient within the atmospheric marine boundary layer are presented. The extinction coefficient profiles are calculated using Klett's inversion method. The variations in aerosol optical properties caused by the underlying surface are studied. Constant-elevation cross sections of extinction distribution along different azimuths over land and sea surfaces ((sigma) equals 0.23 divided by 0.14 km^-1 and (sigma) equals 0.2 - 0.29 km^-1 over land and sea respectively) are presented and analyzed.

Lidars and widely used for investigations of dense atmospheric objects (fogs, clouds, smoke trails) both for the needs of meteorology and ecology. The polarization studies give additional information about the optical and microphysical properties of the observed objects and phenomena. Two main factors determine the polarization state of the backscattered laser radiation: the shape and size of the scattering particles and the multiple scattering effects. The present work aims at determining the prevailing contribution of one of the factors in different atmospheric situations. Radiative fog and Sc clouds have been investigated by means of polarization aerosol lidar. The multiple scattering contribution was studied by varying the viewing angle of the lidar. On the basis of the lidar data an empirical relation is proposed describing the dependence of the lidar signal depolarization on the viewing angle. On the basis of the particular depolarization coefficient values obtained conclusion is drawn up about the phase composition of the cloud formations.

The feasibility is estimated of an approach for measuring the atmospheric wind velocity by spatial filtration of moving turbulence-induced cross-section speckle structure of a propagating laser beam. It is shown that there are some optimum relations between the atmospheric conditions (turbulence intensity, transversal wind velocity) and the experimental arrangement parameters (characteristics of the laser beam, receiving optical system, spatial filter, beam propagation distance etc.), that ensure a maximum measuring sensitivity.

We report new aspects of application of pulsed GaAs diode lasers, concerning absorption spectroscopy of water vapor of third oscillatory molecular overtone 8990 - 9012 angstroms, and Mie-scattering lidar signal in the 15 km range. It is accessible by the power characteristics of a system utilizing the powerful `chip-stack' GaAs diode lasers, employing optimal photodetection technique based on an analyzing system with computer operated boxcar. Data on atmospheric aerosol backscatter signal acquired by DL lidar are presented with relevance to the potential of complex atmospheric remote sensing. GaAs diode lasers, with radiation matching water vapor spectrum of absorption- coefficients of 0.5 - 5 km-1 in Beer's law, are shown feasible for DIAL monitoring of atmospheric humidity.

The preliminary results obtained during the experimental campaign `LIRADEX'98' are presented. A vertically sounding aerosol lidar and an infrared optical radiometer were used to investigate low clouds. Both devices were placed at height of about 12 m above the ground and about 25 m apart. Data about the atmospheric parameters were obtained by parallel standard aerological observation. The experimental campaign extended two weeks--from 06.05.1998 to 19.05.1998. The data presented in the paper are from 08.05.1998.

Novel lidar profiling technique, based on precise measurement of photon arrival times and effective at overlapped photon detector single pulses is developed. Algorithms for determination the individual delays of up to four overlapped events are analyzed and tested. The method meets the main lidar requirements as the very high amplitude and temporal (below 1 ns) resolutions, high tolerable photon rates, short integration times etc.

The feasibilities of a new approach for improving the resolution of coherent Doppler lidars, compared with the known PP-estimator-based approach, are investigated by computer simulations in the case of rectangular laser pulses. This approach consists in employing inverse techniques for retrieving the Doppler-velocity profile on the basis of known pulse shape and estimated statistically autocovariance of the heterodyne-signal profile. The possibility is demonstrated to achieve a spatial resolution cell that is much shorter than the pulse length.

We identify fractal-like behavior in time series recorded by measuring lidar returns. On this basis we propose and ascertain a model for the autocovariance function of the lidar data which explicitly incorporates the approximate self-affine symmetry of the process.

We present an analytical description of the spectral content of the downwelling sky radiance during a total solar eclipse. This work is pointed to prepare the theoretical background for the interpretation of the astrophysical optical and spectrometric observations of the solar corona.

The slope method is widely recognized for handling of lidar signals in homogeneous atmosphere. We propose and investigate a modification of this method that is aimed to evaluation of the extinction coefficient in the center of an isolated aerosol layer. Thus obtained point estimate may be used further as a boundary value in other analytical inversion methods.

The cloud field bottom was sounded in zenith direction by a single-channel IR radiometer which registers the downwelling thermal radiation in the spectral range 7.5 divided by 13 micrometers . The time dependence of the signal is related with the effective radiative temperature of the sounded cloud bottom. The registered records were statistically analyzed. The evaluated statistical characteristics of the signals were analyzed and compared with the information about the morphological structure of the corresponding clouds. It was proved that there exists relationship between the both types of cloud characteristics.

the time mutability method permits drift velocity estimation of statistically non-homogeneous and non-stationary objects. It is an alternative of cross-correlation techniques. Cloud fields are typical objects having the mentioned statistical features. Here we present and discuss results of cloud motion drift velocity estimation obtained by time mutability method based on handling of infrared METEOSAT images.

The slope method is widely used for handling of lidar signals in homogeneous atmosphere. The main goal of the present paper is to investigate the common solution of the lidar equation in the case when the range-compensated lidar return is a linear function of the distance.

Spectra in the visible region measured on board the Vega-2 station are analyzed to obtain the solar spectrum continuum reflected by the dust particles in the Halley comet coma. It is suggested to determine the continuum level for every individual spectrum. By the time of Vega encounter, the concentration and distribution of particles around the comet has changed. This resulted in a different spectral indices for spectra measured in different time. The cumulative size index has been calculated for each specific spectrum by linear regression on the basis of a random number of dust points. Eleven dust continuum wavelengths are selected. The spectral index shows the mean particle size in the line of sight column around the nucleus (values calculated for 1019 spectra are in the interval of 2.85 - 3.48). Its change with the radial distance to the nucleus is discussed. The continuum spectra are calculated with the obtained values of the spectral index and are normalized to the real spectra on the minimum of interval of +/- 15 pixels in relation to the specific dust intensity, with the help of a linear regression. The continuum spectrum follows well the course of the specific Halley's comet spectrum.

The solar wind-comet interaction, one of the basic processes investigated in the cometary physics, may be judged by the ion's behavior. CO⁺ is one of the most abundant cometary atmosphere species. A synthetic spectrum of CO⁺ was created to analyze Halley's comet spectra. The values of some molecular constants were specified in order to improve the accuracy of the computations. It was established that the more appropriate value of the spin- rotational interaction parameter (gamma) for the B²(Sigma) ⁺ state is 0.0192. The use of different values of (gamma) for the higher vibrational levels (v > 0) of the X and B states didn't help for a more precise result. That's why it is recommended to use the same value (gamma) for all vibrational levels of a given state. The value -122.0 was determined for the spin-orbital interaction parameter A of the A²(pi) state. The molecular model, needed to create a spectrum which adequately reproduces the total CO⁺ glow has been specified: v equals 0 divided by 4 for X²(Sigma) ⁺ state, v equals 0 divided by 6 for A²(pi) state, v equals 0 divided by 2 for B²(Sigma) ⁺ state and rotational levels up to N equals 12 for an optimal theoretical spectrum and up to N equals 8 for analysis of Halley's comet spectra registered by the three- channel spectrometer on board the Vega-2.

The importance of the EUV/UV variations for the earth atmosphere is the starting point in this work. Some aspects of the changes in the solar EUV/UV irradiation and the reaction of the earth atmosphere are discussed. It is pointed out that for experiments and modeling of the atmosphere reactions UV proxies are necessary. One of this proxy parameter is the Call-K index. A very good correlation was found for it with the L_(alpha ) and the solar flux in the spectral range of 140 nm up to 200 nm. The Call-K indexes are determined by solar observations. It is necessary to take in consideration the aerosol scattering in order to determine in the plane. A new proposal for the Call-K index determination is made which strongly depends on the spectrum influence of the aerosol scattering, the change of the instrument sensitivity and the instrument offset. It is planned to prove this proposal by Call-K line measurements.

The registration of downwelling sort-wavelength sky radiation during the solar eclipse imposes stringent demands to the measurement equipment. Here we describe a logarithmic three channel radiometer specially designed for the experiments during the total solar eclipse on August 11, 1999.

We report on the ablative etching of Nylon 6.6 [-NH-(CH₂)₆-NH-CO-(CH₂)₄-CO-] at 193 nm and 248 nm, using a pulse discharged ArF and KrF excimer laser respectively. The etch rate at different fluences was determined for both wavelengths, along with other descriptive parameters such as the threshold fluence. The mass spectroscopic analysis showed that even at low laser energies there was a complete braking of the polymer chain bonds at both wavelengths. Moreover it seems that photofragments with two carbon atoms along with the C equals O radical, have a higher probability to be ablated, while photofragments with three carbon atoms appear only under irradiation at 248 nm. No significant photofragments beyond 50 amu were recorded at both laser wavelengths.

Hydroxyapatite (HA), Ca₁₀(PO₄)₆(OH)₂, is the best substitute of the human bone. On the other hand, HA stands for more than 70% from the composition of the bone tissue. We note for HA is friable. Accordingly, it exhibits a very poor mechanical tenure and cannot be used as bulk ceramic for the manufacturing of prostheses. A solution was conceived to surpass this difficulty which resorts to the deposition of HA thin layers on prostheses or pivots of Ti and Ti alloys. The biological tissues enter under these conditions in contact with HA which is perfectly biocompatible. We previously performed Pulsed Laser Deposition (PLD) experiments on Ti, KCl and KBr substrates. We obtained the stoichiometric transfer of HA by PLD in vacuum or by RPLD in (1 - 50) Pa of oxygen, followed by a heat treatment in air. We use an excimer laser source ((lambda) equals 248 nm, (tau) _FWHM >= 20 ns). The incident laser fluence was set an 0.8 Jcm^-2. We report herewith the deposition of a more elaborate structure introducing a buffer interlayer between the Ti substrate and the HA coating in order to improve the quality of HA films and to prevent the diffusion of metal atoms into the deposited layer. The layer was obtained by RPLD from a Ti target in a slow flux of air having a dynamic pressure between the range (4 - 6) Pa. The deposited structures were characterized by electron microscopy (TEM, SAED), X-ray diffraction (XRD) and energy disversive X-ray spectroscopy (EDS) analyses.

We have studied the thermal phenomena implied in the interaction process between the high intensity UV laser radiation and bulk targets. A numerical model for simulating laser-solid interactions has been developed. The phenomena occurring in the target are described by solving the 1D heat equation under conditions of normal vaporization. The calculus was conducted for the case of a Ti and Al targets submitted to a multipulse UV laser irradiation in low pressure nitrogen. In order to elucidate the origin of the droplets, we performed a numerical evaluation of the spatial distribution of temperature reached in the subsurface region. We also analyzed the transit through gas of the ablated atoms and/or of the newly-formed chemical compounds in the case of the ablation of a Ti target in low pressure N₂. This transit was approached with a Monte-Carlo method. We performed Monte Carlo simulations to determine the energy distribution of the atoms and/or of the new chemical compounds at different distances (1.5 - 3) cm from the target surface. The calculation of the energy at which the atoms reach the substrate permits the investigation of the synthesis of TiN and allows the optimum determination of target-collector separation distance. The results we obtained are in reasonable agreement with the experimental determinations.

Carbon nitride thin films are candidates for various technological applications. Special kind of a-Cn_x film, as (beta) -C₃N₄, is supposed to be material exhibiting extreme hardness--higher than diamond. Many groups are trying to synthesize a-CN_x films (with goal of creation (beta) -C₃N₄ phase), but concentration of nitrogen in films is still low. We have created series of nitrogenated amorphous carbon films in nitrogen atmosphere from graphite target by pulsed laser deposition. Additional DC and RF discharges were ignited in order to increase the reactivity of the nitrogen. Film properties were analyzed by X-ray diffraction and spectroscopic ellipsometry. The effects of the discharges on the C-N stoichiometry and on chemical bonding were studied. The N/C ratio increased with higher RF and DC plasma densities up to value of 0.25. Maximum values were reached at the nitrogen pressure twice lower for rf discharge than dc discharge assisted deposition. C-N stoichiometry and chemical bonding were investigated by Fourier transform infrared spectroscopy, X- ray Photoelectron Spectroscopy and Raman spectroscopy. Only films deposited at higher rf plasma power density showed the presence of triple bonded C equalsV N stretching mode.

Thin films of BaTiO₃ were deposited by KrF excimer laser ablation (248 nm) on Si substrates at different substrate temperatures and various oxygen pressures. The process of ablation of the ceramic BaTiO₃ targets were investigated. The composition was measured by EDX microanalysis. The morphology and optical properties of the films were analyzed by SEM and ellipsometry respectively. The dielectric constant was estimated by LCR meter.

Formation of clusters of vacancies in crystalline CoSi₂ has been attained by Q-switched YAG:Nd laser. The X-ray diffraction, atomic force microscopy and electrical resistance measurements, and infrared reflection spectra give evidence of formation of Si vacancies. By laser treatment with intensity ranging from 20 to 50 MW/cm² in air the magnitude of the resistance of the CoSi₂ layer increases approximately by a factor of three, in liquid nitrogen medium approximately by a factor of five. The second task of the present study has been to use the pulsed laser treatment of approach as much as possible the zero value of thermal coefficient of resistivity (TCR) of a Co- Ti-Si layer. The TCR of a Co-Ti-Si layer subject to previous treatment for 30 min at 460 degree(s)C becomes smaller than 10^-5 K^-1 after irradiation of nine 150 ns CO₂ laser pulses of the intensity I equals 1 MW/cm².

The values of absorption coefficient of PLZT ceramics at selected wavelengths in the 0.478 - 1.06 micron interval and at 5.56 microns have been obtained by laser calorimetric measurements. Continuous spectrum of extinction in the 0.37 - 6.5 micron interval has been measured by a spectrometer. The values of scattering coefficient were obtained by subtraction the experimentally measured absorption from the extinction. The values of scattering coefficient at (lambda) < 0.478 micrometers were calculated on the grounds of Usov- Shermergor theory of light scattering in ferroelectric ceramics and were used to obtain the values of the absorption coefficient in the shortwave end of the spectrum. Absorption coefficient was found to follow exponential law with fracture point at hv equals 3 eV and two characteristic (Urbach) energies (Delta) E₁ equals 106 meV and (Delta) E₂ equals 238 meV. Results are explained by high concentrations of two kinds of defects: Pb vacancies and Ti vacancies being responsible for deep acceptor levels in the energy gap. The concentration of Pb vacancies estimated by the Bonch-Bruyevich random field model has been found to exceed the concentration of Ti vacancies by a factor of 7.6.

The waveguiding films of YAlO₃ and Y₃Al₅O₁₂ doped by Nd were directly deposited on (0001) and (1102) sapphire substrates by a pulse laser ablation. The waveguiding properties were measured by m-line technique. The increase of the films refractive index by (Delta) n equals 8 X 10^-3 was observed with the change of dopand Nd concentration of 0.16 at.%. Waveguiding losses lower than 1 dB/cm have been demonstrated at 1.06 micrometers wavelength. The nonuniformity of the thickness was determined by prism-film coupling method. Plasma plume distribution as cos²⁸((theta) ) was calculated.

Light propagation in optical films grown by pulsed laser deposition was studied numerically. We found that the natural curvature of this films introduced during the growing procedure can lead to an increase of the confinement factor of the optical radiation, which increases the pumping efficiency of the planar waveguide lasers. Moreover, the film curvature does not affect significantly the overlap of the pump and the signal fields inside the active layer.

Polymethylmetacrylate with covalently bound side-chain azo- benzene group is synthesized and thin films are fabricated. Holographic grating recording is achieved with a 442 nm He- Cd laser at three different grating spacing: 646, 1340 and 2220 nm. The dependence of the diffraction efficiency on time is investigated. The optical recording is stable for more than four years at room temperature. Optical erasure can be performed with circularly and linearly polarized laser light.

Holographic characteristic of not-fixed and fixed holographic records in Bi₁₂TiO₂₀ crystal has been investigated. A long-term readout photorefractive memory, implemented in this crystal, has been proposed and demonstrated. The effect is achieved by reading the recorded and fixed hologram with a low-intensity light wave and by additionally amplifying the reconstructed image. Recording and amplification are performed in one and the same crystal. A good quality of the reconstructed image is demonstrated after 60 min of continuous readout of the photorefractive grating.

Volumetric structures consisting of multilayer clads made of the bronze B10 and also of stellite SF6 alloys are prepared by laser remelting of the metal powder of the original particle size of ca 60 micrometers injected into the processing zone through a conical nozzle. For remelting with a cw CO₂ laser beam of intensities around 10⁵ W/cm² and sample feed rates not exceeding 2.5 cm/s an efficient formation of the structures is observed and their geometry can be controlled. A fine grained, dendritic microstructure of the samples is observed by means of the optical and scanning microscopes. In the AFM scans the characteristic dimension of ca 60 nm reproduced in the periodic structures of the SF6 surface corresponds most probably to crystallines formed due to segregation after the liquid-solid phase transition. Similarly to SF6 the powderized B10 material is well suited for a fast prototyping.

We report on the use of an epoxy novolac chemically amplified photoresist to produce X-ray images of living biological specimens in the water window using laser plasma generated soft X-rays (2.4 - 4.4 nm). The photoresist response was at least one order of magnitude `faster' than the standard PMMA (polymethyl methacrylate) previously used in soft X-ray contact microscopy. After chemical development of the exposed resists, atomic force microscopy (AFM) of the relief images obtained of biological specimens clearly showed the flagella of the motile green alga, Chlamydomonas, suggesting a lateral resolution better than 200 nm, whilst the AFM was capable of discriminating height features of 20 nm in depth profiles.

Many factors are involved in a relatively new tumor treatment modality, the photodynamic therapy (PDT). Among them the most important are the laser parameters (wavelength, energy fluence), the photosensitizer cytotoxic and optical properties, the delay between drug injection and PDT and the effective dosimetry of both light and drug distribution in the treatment target. In this work, we compare the effectiveness of two methods of predicting the concentration of the photosensitizer m-THPC in tissue simulators. In the first method, a conventional double beam spectrophotometer was used to measure the absorption in UV- VIS of the soft tissue simulators, prepared with agar gel with different concentration of m-THPC. In the second method, the laser induced fluorescence spectra of these samples were recorded and an effort was made to determine from these the optical properties of the samples, in order to calculate the required drug concentration in vitro. The experimental results are discussed in conjunction with the appropriate theoretical models.

A computerized surgical laser system is created. It is designed to function both at the basic wavelength of 1.06 micrometers which exhibits photocoagulatory effect on the biological tissue and at the additional wavelength of 1.32 micrometers which has a cutting action, similar to that of CO₂ lasers. 200 operation have been performed of patients suffering from 22 diseases.