The development of precision optical frequency standards is reviewed with emphasis to standards based on laser cooled and trapped atomic ensembles. As a typical example, an optical frequency standard based on laser-cooled and stored Ca atoms is presented. The use of optical frequency standards requires the knowledge of their frequencies. Methods and proposals for the synthesis of optical frequencies like harmonic mixing, mixing of subharmonics, cascaded frequency interval division, and wide band frequency modulation are discussed. A phase-coherent frequency measurement of the Ca optical frequency standard is demonstrated representing the first phase-coherent frequency measurement of visible radiation related directly to the primary standard to time and frequency.

This is a review of the recent investigations on He- Cd⁺, He-Kr⁺, He-Ar⁺, He-Se⁺ and He-Cu⁺ lasers excited with the transverse capacitively coupled radio-frequency discharge. The recent investigations show that the designs and operation of the radio-frequency excited lasers are much simpler than those of the hollow-cathode discharge lasers at the similar laser output parameters. Under single-line operation the radio- frequency excited He-Cd^P+ laser delivers output powers of 60 mW at 441.6 nm, 36 mW at 469.4 nm, and 11 mW at 431.8 nm. Both lasers exhibit the rms noise-to-signal ratio much lower than that of conventional positive column He- Cd⁺ lasers. These make the radio-frequency excited ion gas laser attractive for practical applications.

Emissions from charge transfer states of rare gas halide RgX molecules in rare gas solids and also of alkali halide ions AX combine the known properties of short wavelength, gas phase excimer lasers with high densities of excited states attainable in the condensed phase. In Ar and Ne crystals binary doped with XeF and F₂ a XeF density of 10¹⁸ cm^-3 is prepared. This high density together with a quantum efficiency close to 1 provides large measured gain coefficients between 11.6 and 2.4 cm^-1 for the D-X, B-X, C-A and D-X transitions of XeF in Ar and Ne solids, respectively. Lasing with quantum efficiencies up to 14 percent occurs and beams of low divergence of 3 mrad are extracted with interferometric cavities.Inhomogeneously broadened spectral profiles and relaxation oscillations are observed in the C-A laser emission of XeF in Ar. Concerning alkali halides the e-beam excitation of Ne and Ar matrices doped with 0.4 to 0.7 percent CsF or CsCl results in the deep UV emissions located at 196.5 nm, 220.3 nm, and 211.2 nm and also at 227 nm which are ascribed to the B²(Sigma) _1/2-X²(Sigma) _1/2 and C²(Pi) _1/2-A²(Pi) _1/2 transitions of the ionic A²⁺X^- states, respectively.

A theoretical approach for investigation of amplitude and polarization behavior of a vector class-A laser based on the Hones matrix and vector formalism is considered in details. Exact mathematical expression for a new decay rate-decay rate of the electromagnetic field polarization is derived. It is shown that this constant might be strongly influenced by resonator anisotropy. Amplitude and polarization behavior of the vector laser model taking into consideration the decay rate of the field polarization is investigated for two particular cases of He-Ne slightly anisotropic lasers operating at (lambda) equals 1.15 micrometers and at (lambda) equals 1.207 micrometers .

The paper deals with measurements of excitation spectra of forbidden transitions in di- and poly-atomic molecules in a supersonic beam. The molecules were excited using pulsed tunable dye lasers directly in the following forbidden transitions: B'² (Delta) $IMP X²(Sigma) in the case of CaF and CaCl molecules, and S₀(¹A_1g) yields T₁ (³B_3u), S₀(¹A₁) yields T₁ (³B₁) and S₀(¹A_1g) yields T₁(³A_u) transitions in the case of pyrazine, pyrimidine and glyoxal, respectively. The spectral resolution of our set-up allows determination of energy values and rotational constants for the two spin-orbit levels of the CaF and CaCl molecules. For the CaCl molecule the rotational constants of the vibrational v" equals 0 level of the B' (²(Delta) ) state have been determined for the first time. The excitation spectra of pyrazine, pyrimidine and glyoxal in the range between the S₁(0₀) 0 T₁(0⁰) yielded frequencies of fundamental vibrations, which for pyrazine and glyoxal are in a good agreement with literature values, but for pyrimidine were determine for the first time. Both types of phosphorescence spectra exhibit many hot bands besides the fundamental, totally symmetric, vibrations. The hot bands are very helpful in supporting the fundamental mode assignments.

A new system, constituted of a double channel Fabry Perot etalon and laser diodes, is described and proposed to be used for air refractive index measurements. The principle of this refractometer is based only on frequencies measurements. It permits instantaneous measurements with a relative standard deviation in the range of 10^-9. Some preliminary results on the stability of this systems are presented.

The advent of depth-resolving, remote measurement techniques for the determination of atmospheric constituents added a new dimension to the investigation of atmospheric phenomena. In this paper optical, or lidar, techniques suited for this purpose are reviewed. After a presentation of the processes used and the algorithms necessary to extract the interesting information from the optical return signals, a few considerations about the necessary instrumentation are presented. For illustration, one example is shown of results obtained with elastic backscatter, differential absorption and scattering. Raman lidar, and Raman DIAL. Of the numerous new developments in actual progress, one example, BELINDA, has been chosen that in a way marks the borderline between elastic backscatter and differential absorption lidar.

Properties and data of materials for creation of planar waveguide lasers and properties of suitable substrates are summarized. Parameters of published lasers are overviewed. Parameters of active and passive planar waveguides created by method of pulsed laser deposition are described. Results of our experiments of laser deposition of thin Ti:sapphire layers on quartz substrates are presented. Up to 4 waveguiding modes in created layers were observed and attenuation of 6.8 dB/cm was measured.

The review of theoretical and experimental investigations on maskless formation of submicron periodic relief gratings on the surface of A^IIIB^V semiconductor materials, carried out in the Scientific Research Center for Technological Lasers of Russian Academy of Sciences is presented. The lecture is based on the materials, which were presented in the original papers. The revue of the literature can be found in the above references.

Pulsed laser beams, of very short duration, appear to be very promising tools for polymer surface processing. Recently we have studied the interaction of picosecond and femtosecond laser radiation in the visible region of the spectrum with synthetic polymer films and we have compared these studies with our similar studies with nanosecond duration laser radiation. Biocompatible polymers have been extensively used for sutures, vascular grafts or bone and other hard tissue replacements. The use of surgical lasers for intervention on biocompatible material - tissue interfaces has attracted a great deal of interest, as both the high intensity, short pulse duration lasers and the prosthetic biomaterials are in increasing use. Our recent ablation studies, using ultrashort laser pulses, of biocompatible materials, are described in this article. Lasers were introduced in medical research in the early sixties but the laser beam ability to remove efficiently and safely soft or hard tissue, the lateral thermal damage and the final surface characteristics are still under investigation. In the past few years, by virtue of their water or water and hydroxyapatite content respectively, exhibit strong absorption restricting residual thermal damage to a relatively small zone. Recently we have investigated the interaction of short pulse laser radiation of picosecond and femtosecond duration with soft and hard tissue, as this unexplored field is expected to be a potential alternative in powerful laser processing of biomedical structures. The experimental results obtained, including ablation rates, ablation wavelength dependence, pulse duration dependence, fluence dependence, etc. are presented. These results are discussed according to simple theoretical models of laser energy absorption and the possible mechanisms of ultrashort pulse laser ablation, which in some cases involves multiphoton photodissociation processes. Finally, the design characteristics of the lasers employed in our experiments, are stated briefly.

A record average output power as high as 120 W was achieved for a CuBr laser. The high-power CuBr laser produced output powers of 100 W at an efficiency of 3 percent, and 120 W at 2.5 percent, respectively.

Laser oscillation on the 780.8 nm copper ion line was investigated using capacitive coupled radio frequency (CCRF) discharge excitation. Laser action was obtained at cw, quasi-cw and pulsed mode of excitation. The optical for lasing conditions were determined. A small-signal gain of 25 percent/m was measured at optimum laser conditions. The high gain and the stable operation offer good possibilities for UV lasing in Ne-Cu CCRF-excited discharge.

Water-cooled stable operating at average powers of 0.6-1.1 W, Sr⁺ recombination laser with independent production of Sr vapor is reported. Some features of the discharge tube construction and the laser operation are given. It is found that the application of the water cooling enables a higher input power loading for optimum tube-wall temperature. At Sr⁺ laser with independent production of the metal vapor it is possible to control the concentration of the Sr vapor and to inhibit the effect of overheating on lasing. This peculiarities result in an increase in the average laser power and an improvement of the laser operation stability.

Laser action in the soft x-ray and ultraviolet spectral regions is a subject of a number of papers, since this radiation is used in different types of experiments as well as in different type of technological devices. It is well known that one of the possible mechanisms for UV, VUV, and soft x-ray lasing is based on the process of ejecting one of the inner shell electrons. In this work, we propose the explanation of the laser action on nd⁸(n + 1) - nd⁹(n + 1)p electron configurations of ZnIII, CdIII and HgIII. The explanation is based on the information of atomic constants. In ZnIII and HgIII cases, different excitation sources were used, but the same excitation mechanism is a background. The similar electron configurations, which could be possible candidate for laser action will be discussed in the case of CdIII spectrum. The corresponding wavelengths are in the spectral interval below 300.0 nm. Based on the information available for the above mentioned electron configurations of ZnIII, CdIII and HgIII, a conclusion is drawn, that the same physical background is proposed for all discussed spectra.

Experimental and theoretical investigations were made of a radial inhomogeneity of the gain in a cw CO₂ laser with fast axial flow. The results showed that this inhomogeneity was the result of a radial inhomogeneity of the temperature and of contraction of a longitudinal self-sustained discharge towards the axial region in a gas-discharge tube. This caused saturation of the rise of the small-signal gain when the discharge current was increased. It also reduced the rate of the output radiation power with increase in the input energy when the fundamental Gaussian mode was generated.

The present work is aimed at investigating some important characteristics of standard two-mode laser tubes with internal mirrors of their frequency stabilization and their comparison with the Bulgarian-made He-Ne tube LXH-202M.

We demonstrate how a pulsed two-wavelength tunable Ti:Al₂O₃ laser can operate at near maximum efficiency, obtained in an optimized non-selective cavity. To achieve this efficiency we solve the intrinsic of the Passive Self- Injection Locking (PSIL) method problem of non-controlled free lasing at high pump level by combining the PSIL control with an appropriate dual-pulse pumping. Laser efficiency is increased and the background emission is limited to less than 1 percent in a region ten times larger compared with the standard PSIL control. From analysis we have found optimum conditions and show the advantages of this combined technique. The proposed approach is compared with spectral control of a Ti:Al₂O₃ laser, realized by injection from a coupled two-wavelength dye laser.

A theoretical model describing the mode competition in two- wavelength-injection-seeded pulsed dye lasers is reported. Expressions for both the instant powers during the FO's pulse and final energies of the two injected spectral lines, as a function of readily-measurable experimental parameters are obtained. The results of computer calculations using the model are shown and discussed. An experimental verification of the developed model for the case of Nd:YAG-laser-pulsed dye lasers shows a good agreement with the theory.

An injection seeding of narrowband and broadband radiation into a highly selective tunable laser is described. An increase of the laser output energy by a factor of 1,5 is achieved. Laser oscillations are induced by injection seeding when the active medium is pumped below the laser threshold. Optical signal as small as 0.2 nJ is detected and amplified by a factor of 150.

A novel approach for narrow-line selection and wideband tuning of lasers using a self-selection interferometer is applied to obtain a high spectral purity emission. A comparison on the base of the background emission level is made between a proposed and a conventional cavity scheme with same selector. The results of theoretical investigation and experiments show a decreasing of the background emission in more than two orders of magnitude for the new realized scheme. Such kind of lasers are of special interest for application in Raman spectroscopy and isotope separation systems.

The optical properties of the interference wedges are analyzed in the case of restricted laser beam illumination. The results of computer simulation of intracavity selection with Fizeau wedge are present in the report. There are calculated transmitted beam profile for typical intracavity laser beam diameters for Gaussian intensity distribution. Certain dependencies concerning the wedge thickness and incidence angle for dual laser technology application are obtained.

Optical parametric oscillator based on LiB₃O₅ (LBO) crystal and synchronously pumped at 532 nm by second harmonic generation of Nd:YAG mode locked laser, is described. In the xy plane, we use type I nonlinear interaction. Using the Sellmeier equations for the principal refractive indices of LBO, the phase-matching is calculated and the tuning curves within all transmission range are obtained. Temperature-tuning within 120-180 degrees C for the crystal is applied, and a precise thermostabilization of the heating is also realized.

Analytical formula using elementary functions for the description of the process of nonlinear phase shift of the fundamental waves involved in second harmonic generation or sum frequency mixing have been derived. The analytical results can be used for the design of devices based on cascade second order nonlinear phase shift. Using this formula it is shown that the system 'polarizer-Type II SHG crystal-analyzer' possesses pulse compression capability.

In this work we explore the optical properties of a thin interferential wedge with a saturable absorber in the gap. The knowledge of wedge transmission as a function of nonlinear absorption in the gap is essential for creation of interferometric devices for direct control of high power light by light with many times lower power. Such devices exploit the fact that two light beams can penetrate in different ways in the interferometer gap. With a view to this, we consider the wedge illuminated by a high power beam falling quasinormally on the interferometer surface when the same gap region is simultaneously illuminated directly by the low power beam. To evaluate the dependence of transmission of the high power beam on the absorption, we propose a technique for calculating the nonlinear attenuation of multiple beams in the gap. The analysis of the wedge's behavior is made using the approach derived by as for restricted laser beam illumination of the assumption of truncated Gaussian amplitude distribution and uniform phase distribution. The cases of linear and nonlinear absorption, as well as saturation of the absorber as a function of variations of the low-power beam are analyzed.

The first investigation on the nonlinear optical properties of Magnesium sulfite hexahydrate monocrystals are reported. The crystal has been grown, for the first time according to our knowledge, by our new original method, that allows them to reach up to 40-50 mm linear size. Both Type I and Type II phase matched effective second harmonic generations are observed when the crystal is pumped with Nd:YAG laser radiation. First data for MgSO₃6H₂O indici of refraction dispersion and for its second order susceptibility tensor components are presented.

The effect of pre-chirping on soliton switching dynamics in nonlinear directional coupler using the direct numerical solution of the system of nonlinear Schrodinger equation is considered.It is found that the initial pulse chirp dramatically change transmission characteristics. As a rule, switching of a down-chirped pulse occurs at a higher critical power. Switching of weekly up-chirped pulse occurs at a lower critical power. The effect of pre-chirping of a week control pulse on transmission characteristics is studied and the possibility of chirp-controlled switching is investigated. It is less effective than phase-controlled switching. A symmetry-breaking instability for chirped pluses is studied. It is found that intensive energy exchange takes place even the pulse amplitudes are below instability threshold. The influence of polarization state on the switching of a chirped pulse is investigated.

A set of two coupled nonlinear Schroedinger equations, describing nonlinear propagation in strongly birefringent and multimode optical fibers is analyzed by means of Lie group technique. As a result complete list of group- invariant exact solutions is obtained. A new exact solution is presented. The so-called symbiotic periodic and soliton solutions are included in this classification in natural ways. Laws of conservation are also derived.

Variable number os quasi-2D dark spatial solitons of adjustable transverse velocities could be generated by a proper choice of the initial phase profile and width of crossed dark stripes and the background-beam intensity. The possibility to branch single input probe beam into ordered structures of subbeams is demonstrated numerically in bulk self/induced-defocusing Kerr nonlinear media.

The feasibility to stabilize ensembles of optical vortex solitons with respect to their positions on a common background beam is numerically demonstrated. The topological charge of the vortices is found to rule the propagation characteristics of the ensemble as a whole. The most stable configurations regarding ensemble rotation/repulsion are discussed.

We present experimental results on the evolution of ring dark solitary waves and optical vortices generated by computer-synthesized holograms. The detailed comparative numerical simulations show, that this approach ensures reproduction of the correct intensity and phase portrait of the dark waves at the entrance of the nonlinear medium. The transverse dynamics at both even and odd initial conditions is studied and compared with the theory and simulations.

In this paper a new kind of device - a gradient distributed fiber amplifier -is proposed and analysed. In such an amplifier the concentration of the dopant ions increases along its length in the direction of pump power decrement, in a way that ensures nearly constant signal gain coefficient in every point of the fiber. Hence, an optimal amplification configuration that simultaneously minimises the influence of the background attenuation, the soliton self-frequency shift and the third order dispersion on the solitary signal pulses can be chosen and maintained in such device. Although in the general case the perturbations cannot be completely canceled4 ,the results of the computer model clearly show that a gradient fiber amplifier can be designed as a transparent transport media for high-speed, long distance optical fiber communications. Keywords: optical communication lines, solitons, Er3-doped fiber amplifiers.

The laser induced fluorescence spectrum of K₂YF₅:Nd³⁺ (PFYK:Nd) single crystal, pumped by the fluorine F₂ pulsed discharge molecular laser at 157.6 nm, was obtained in the Vacuum Ultraviolet (VUV) region of the spectrum. The fluorescence peaks were assigned to the 4f²5d yields 4f³ dipole allowed transitions of the Nd³⁺ ion. The absorption spectrum of the PFYK:Nd crystal samples in the VUV spectral region was obtained as well. The transitions between the ⁴I_9/2 ground level of the Nd³⁺ ion of 4f³ configuration and the levels of 4f²5d configuration were observed for these crystal samples, to our knowledge for first time. The electric crystal field splits all the levels of single and mixed configuration. The number and the spacing of the components depends on the symmetry and the intensity of the crystal field. We found that the 4f²5d levels of the Nd³⁺ ion, split into eight components in the PFYK host lattice. The edge of the 4f²5d levels of the Nd³⁺ ion in the PFYK crystal host was found to be at 54940 cm^-1. Furthermore, we report on the interconfigurational 4f²5d yields 4f³ VUV fluorescence characteristics of the PFYK:Nd crystal under excitation form the pulsed discharge F₂ molecular laser operating at 157.6 nm. The concentration of the Nd³⁺ ions in the crystal sample was 0.1 percent. The sample was an optically polished disk having a diameter of 5 mm and thickness of 1.2 mm. The experimental set up consisted mainly of the F₂ pulsed discharge molecular laser, a hydrogen lamp, an XUV- VUV monochromator, and the necessary electronic equipment for detecting and recording the spectrum. The laser source delivers 12 mJ per pulse and only 1 mJ, after focusing, was used to excite the crystal samples. The spectra were detected with a resolution better than 0.5 nm.

A compact and economic system is proposed for diode laser single-longitudinal-mode selection, oscillation linewidth narrowing and frequency tuning by means of feedback from a diffraction grating in Littrow configuration. For single- mode frequency tuning, an electromagnetic driver is applied which provides a few hundreds of microns change of the diode laser external cavity length. Continuous frequency scans over 50GHz are realized. Improved shape and coincidence with the diode laser axis of he output laser beam is achieved by means of 1 mm aperture in the diffraction grating. Laser wavelength measurement is performed using high diffraction orders of a diffraction grating with small period. The performance of the system is demonstrated resolving I₂ and Na₂ ro-vibrational absorption spectra in the spectral region around 670nm. The identified I₂ absorption spectrum can be applied for diode laser stabilization at many points of their tuning regions with known absolute wavelengths.

We report magneto-optical rotation due to the interaction of atoms with a resonance laser beam. Our experiment is performed on the excited He states, 2³P-3³D transition, (lambda) equals 587,56nm. Two processes are responsible for the magneto-optical activity: the Zeeman coherences, induced in the absorbing level, and the optical pumping processes, each of them due to the laser beam excitation. The Zeeman coherence creates peaks with a width determined by the coherence relaxation rate, while the optical pumping creates a structure with a width in the order of the natural width of the transition. Due to the difference between the relaxation rates of the 2P and 3D He levels, the two parts of signal are well resolved and depend on the He pressure in different ways. The narrow coherence signal disappears at high He pressure, unless the amplitude of the optical pumping signal increases. The optical pumping signals saturates as He pressure increased and changes its sign. At high gas pressures, such that only the optical pumping signal exists, an increase of the He pressure leads to the narrowing of both the 'classical parabolic dependence' and the optical pumping signal.

The He(s$_1,3)S, 2^1,3P) states play a significant role in different type discharges, including laser media. There are not data in the literature for quenching of these states by atoms of rare earth elements (REE). One could not also find information about quenching of He(n^1,3S, n^1,3,P; n equals 3-6) states by REE (Eu and Yb) atoms. These states determinate the population of low lying He(2^1,3S, 2^1,3P) once.In this paper the theoretical calculations are done, taking into account different quenching channels. THe experimental method for investigation of He(n^1,3S, n^1,3P; n equals 2-6) states is presented. A computer model of the processes of interaction of low lying He states with Eu is developed.

Investigations of the behavior of mercury transitions are reasonable tasks for improvement of different types of light sources as well as for solving environmental problems. Recently, the time behavior of the 546.0 nm spectral line was studied after two step pulse laser excitation of the 7³S state via the 6³P₁ state. A nonmonotonical decay of the population of 7³S was observed and was interpreted as a results of the stimulated emission in forward direction of the excitation laser beam. In our experiment we observe the nonmonotonical behavior of the decay of the 546.0 nm spectral line intensity when the 6³P₁ state is excited by strong pulse laser beam. This behavior is changing when the wavelength of excitation laser beam is tuned around the 253.6 nm wavelength. Some hypothesis for explanation of this behavior is given.

Resonances with complex shape have been obtained experimentally in the magnetic field dependence of the optogalvanic signal induced in a Cu/Ne hollow cathode discharge by 632.8 nm laser radiation. Either population trapping or transfer of coherence are considered as possible mechanisms of formation of these resonances. Both of them, however, appear insufficient to obtain full qualitative explanation of the observed dependencies.

The dynamic optogalvanic signals from N₂ and (N₂ + He) mixtures have been registered as a function of discharge current and laser pulse energy in a hollow cathode discharge. The time-dependent optogalvanic signals obtained in this investigation are a good basis for an interpretation of the optogalvanic effect from molecular nitrogen.

The appearance of an optogalvanic response of dumping oscillating type in a hollow cathode discharge is considered. Having analyzed the transient processes in the electric circuit, including the gas discharge cell, the oscillating response is found to be connected with the negative resistance of the discharge and with other circuit elements. The results are compared with measured photoemission dynamical optogalvanic signal. An optical method for probing of light absorbing gas discharge is suggested. It is based on the light induced response of the spectral line intensity. The sputtered atoms of magnesium are taken to probe an illuminated Ar/Mg hollow cathode discharge.

Preliminary results of restoring potentials of interactions Na(3s, 3p)-CO₂(X¹(Sigma) _g⁺) from measured far wing spectra of sodium resonance line Na-D perturbed by CO₂ are presented. The spectra in the range of (Delta) (sigma) approximately equals 10-3500 cm^-1 are considered following the quasi-static theory of line broadening by inert gases as continua and due to the A $ARLR X and B $ARLR X transitions of Na-CO₂ quasi-molecules. The reduced absorption coefficient K((sigma) ) at frequency (sigma) equals (sigma) ₀ + (Delta) (sigma) is calculated as corresponding to the radiation from molecules with internuclear separation R, where hc(sigma) equals V^A,B - V^X. As a first approximation, all the three potentials are presented in the shape of a (6,12)-Lennard-Jones potential. The constants C₆ and C₁₂ are determined as independent variables by minimization of the sum of squared deviations between measured and calculated K((sigma) ). Four versions of minimization were considered successively: (1) only red wing, (2) only blue wing (3) both blue and red wings with 6 independent variables (C₆ and C₁₂), and (4) both wings with fixed C₆. The calculated K((Delta) (sigma) ) are compared to the measured ones.

The effects of the direction of propagation of the optic wave, the length of acousto-optic interaction and the power density of the controlling RF-signal on the spectral response of a noncollinear acousto-optic tunable filter of TeO₂ is discussed and illustrated from the viewpoint of practical applications. An example of filter design using these dependencies is presented. The calculated spectral characteristics of the bandpass width, the spectral resolution and the diffraction efficiency are compared with those measured experimentally. It is shown that the calculated spectral characteristics describe well the experimentally measured ones for a filter prototype.

Performance of CO₂ doppler lidar for fixed hard target at low laser frequency stability is presented using the novel wide-band doppler detection technique described before. The approximate maximum likelihood estimator is used. The velocity estimation error is experimentally determined at various SNRs and is compared to the Cramer-Rao Bound. Our results show a deviation of the unbiased velocity error from the CRB less then the width of the confidence interval for the error. The biasing of the estimator at low SNRs is studied experimentally for non-ideal equipment performance; we propose the Gaussian model of the distribution of so called 'bad' estimates are more appropriate for experimental data, instead of the uniform one recommended.

In the paper some results of polarization investigations of various objects and phenomena in the atmospheric planetary boundary layer performed by a ground-based lidar are presented. An attempt is made the frontal zone passing to be followed in more detail. The dynamics of the cloud system formation is observed. Differences between the optical properties of the aerosol near the clouds base and top are established; through the depolarization coefficient changes within the clouds the phase composition of the latter is determined.

This paper presents some results of an elastic- backscattering lidar experiment carried out in the Bulgarian Black Sea coastal area in September 1992. The distribution of aerosol within the planetary boundary layer is studied following the variations of the lidar return signals. A combined interpretation of the lidar data with conventionally measured meteorological parameters is made. The obtained results prove the ability of the lidar the cases of sea-to-land and land-to-sea breezes to be distinguished. Based on the changes of the backscattered return signal the prevailing effect of the radiative or advective processes is determined. An attempt is made the height of the thermal internal boundary layer near the shore line to be determined.

The intensity fluctuations of laser beam cross section caused by a local air turbulence have been experimentally investigated. Registration of successive saturated images of the laser spot has been provided by imaging camera using a computer for image acquisition and processing. Evaluation of the state of turbulence by estimation of the refractive index structure parameters has been carried out.

A type of exponentially-shaped sensing laser pulses is shown to lead to simple, accurate, and fast deconvolution algorithms for improving the lidar resolution. In this way the possibility is pointed out and illustrated to achieve accurate and fast investigation of the fine spatial structure of atmospheric and other objects by use of controlled, well-defined and reproducible pulses of the sensing radiation.

The problem for improving the temporal resolution of highly dynamic backscattering signals is important in the remote probing of the atmosphere. The use of inverse methods in lidar receivers is one of the novel approaches to improve their performance at arbitrary photon rates. In previous works we have developed a model of a lidar receiver based on the excitation of decayed oscillations in a set of resonators and the use of inverse algorithms for retrieving the lidar profile. In this work we present the experimental results obtained with the specialized receiving system developed according to the above model. It makes use of low frequency non-Fourier eigensignals of periods larger than the observation interval.It is shown that the profiles of electrical pulses may be resolved by 50 ns resolution at 10 frequencies below 1 MHz.

The work presents results of simulation of processing of wideband doppler lidar signals by analog and digital heterodyning at different profiles of the transmitted laser pulse. At assumption of signal statistics determined by the transmitted pulse, the return signals are simulated immediately after the optical mixing in the time-domain using three pulse shapes: rectangular, Gaussian and a CO₂ laser pulse with a tail at different wideband signal-to- noise ratios. Simulation of analog heterodyning includes quadrature detection with reference frequency instability. Simulation of the digital heterodyning includes the direct sampling of the return signal after the photomixer as well as the undersampling of this signal without and with preliminary filtering. The cases of narrow and wide return doppler spectra compared with the Nyquist interval are simulated. The number of generated realizations varies with the signal-to-noise ratio. To compare the vulnerability of the considered processing schemes with the pulse shape a maximum likelihood doppler shift estimate is used. As an output of the simulation the probability density function of the doppler estimate for the ensemble of generated realizations is found.

The use of lidar systems as distance non-contact devices by the control of the parameters of phenomena for ecological protection needs a development of technical capabilities for the realization of that idea. The high dynamics of the process in the phenomena can be measured only with the real- time data acquisition system. The real-time working systems allows an express analysis of lidar information. The lidar signal includes in it information of the parameters of the ecological pollution. In such systems as a control devices are used PCs with special software. The stream of information into the lidar systems usually need tow or more input channels and have an input speed about 20 MB/sec per channel. It is difficult for the PCs to collect that data directly without additional devices.

Pulsed laser ablation is well established as a universal tool for surface processing of organic polymer materials. The effect of pulse duration on the ablation process is extended to ultrashort laser pulses, of picosecond and femtosecond pulse width. The main advantages of using such very short laser pulses for the ablation of polymers is that heat diffusion into the polymer material is negligible an the energy loss into the sample is minimized. As a results the ablation threshold is reduced and also high precision patterning of the sample without thermal damage of the surroundings becomes possible. For transparent materials, in the corresponding ablation wavelengths, the mechanism of ultrashort pulse laser ablation is complex involving a multiphoton photodissociation process. Ablation rates of polymers have been measured by irradiating the polymers with a variety of laser sources. The laser sources use were producing pulses of picosecond and subpicosecond duration, in order to investigate comparatively the ablation efficiency and the phenomenology of the etched patterns.

Two types of thin films with magnetic properties were deposited using XeCl excimer laser ablation. Mn-Zn ferrite films were deposited on Al₂O₃ substrates and perovskite-like films of La_0.8Sr_0.2MnO₃ were deposited on Si substrates. The properties of stoichiometric Y₃Fe₅O₁₂ thin films prepared by KrF excimer laser ablation of targets were investigated. It was revealed that magnetic properties strongly depended on the crystal structure of three types of substrates used. The influence of processing conditions on the magnetic properties was investigated. Magnetic properties wee analyzed using vibrating sample magnetometer. The laser-induced plume optical emission was examined. Ellipsometry was utilized for optical constants measurements.

This work summarized the results of XeCl excimer laser ablation deposition procedure of Ti-doped sapphire thin films. Three types of targets are utilized-monocrystalline and two different ceramics synthesized in vacuum and H₂ ambient. The influence of the target's type in the film quality is studied. The films are investigated by XRD and SEM, as well as by optical methods. Optical emission measurements of laser ablated plumes are performed.

Laser pulsed deposition technique was utilized for preparation of LiNbO₃ thin films on sapphire and GaAs substrates. XeCl excimer laser was used for the ablation of monocrystalline LiNbO₃ target. The deposition was performed in oxygen atmosphere at different substrate temperatures. The ablation threshold was determined from the experimental results presented ablation rate vs. on laser fluence dependence. The films were characterized by XRD, SEM and ellipsometry.

The aim of this work was to investigate the growth mechanism of Y₁Ba₂Cu₃O_7-(delta ) thin films prepared by KrF and XeCl excimer laser ablation on different substrate. To investigate the film's properties - morphology, epitaxy, c-axis length and critical temperature (T_c) - we varied the process parameters - oxygen partial pressure, substrate temperature and laser energy density. The films were analyzed by (Theta) -2(Theta) XRD, (phi) -scan XRD, optical microscopy, AFM, prophilometry and electric measurements.

Laser surface alloying processes all the features of surface melting, plus additional capability of modifying the chemical composition by adding alloying elements which greatly enhance the wear and corrosion resistance of aluminium alloys. This paper is concerned with a study of the formation mechanism and structural changes of the alloyed layer during laser surface alloying aluminium with niobium...The material is formed dendrites of Al₃Nb and a small volume fraction of interdendritic (alpha) -aluminium solid solution...Surface alloying was performed by the blown powder technique using a CW 3 kW CO₂ laser.

A process of laser cutting has been investigated by means of a 3D numerical modelling and a theoretical analysis in terms of Mathieu functions. The mean object of the work is to show and compare the temperature field distributions around the groove obtained by the methods mentioned. The results for the heat flux and the temperature field concern laser cutting if Plexiglass but the methods can be applied also to other materials of interest. It is shown that assuming a moving circular cylinder the analytical solution underestimates the temperature field distribution. It is necessary to take into account an elliptical cylindriform heat source having a proper aspect ratio.

The development of a novel laser-based seam tracking system for real-time industrial robot welding applications is presented. The system is based on a infrared diode laser, able to scan perpendicularly the seam joint using a laser scanner. A dedicated CCD camera collects the reflected laser light and the relative distance of the surface points under the sensor, form the sensor itself, is then calculated by simple triangulation techniques. The features of the seam profile such as the joint position and geometry are extracted and measured, with a precision of a some microns. In this paper the main components of the novel laser-based seam tracking system will be presented, as well as preliminary results obtained by our system. The laser-based seam tracking system will be of low cost, simple to use a nd rugged enough to provide trouble-free service in any welding or hostile industrial environment. This system will be the first to be developed and installed in Greece.

An optical inspection system has been developed to detect the surface quality of flat surfaces. The system monitors surface quality by using a laser scanner sensor which detects spatial differences in the intensity level of the light scattered in various directions. An image processing algorithm has been developed to classify the surface quality either by measuring the average of the intensity difference or by counting the number of defects when a more detailed analysis is necessary.

We report the use of computer techniques for modeling and visualization of the laser monitoring of the inner surface of an operating Bessemer converter. The purpose of the study was to estimate the accuracy of the laser measurement technique, to determine the geometrical parameters necessary, and to establish the requirements to the accuracy of the scanning part of a laser meter when the pulse duration, beam divergence and defects size are pre-set. The following basic conclusions can be drawn: firstly, it is possible to use a laser meter as a device for monitoring the casing thickness based on the use of a pulsed solid-state laser; secondly, the process of non-uniform wear can be handled by means of additional measurements with off-axis sounding geometry; thirdly, the numerical experiment demonstrates that, based on the accuracy achieved of determining the casing thickness, the operating life-time of the converter can be extended.

A noncontact optical sensor for vibration measurement in a broad frequency and amplitude ranges is investigated. The sensor is able to measure vibration amplitudes less than 1 micrometers and up to 5 mm with the upper frequency of 100 kHz. The frequency range of the measured vibration is limited up only by the frequency characteristics of the electronic device. The sensor measures vibration from small area and it might measure vibration from objects of small mass, because no any influence of the mechanical characteristics of the vibrating object.

Spectral dependencies of Verdet coefficient (V) of undoped Bi₁₂SiO₂₀ (BSO) and doped with Fe and Cr BSO crystals are studied. It is established that Cr and Fe change V in BSO in the spectral range 440-700 nm. It is found that for doped crystals the Faraday rotation angle is not a single-valued function versus the magnetic filed. The magnetic field scanning causes deep hollows in the light power. This effect is strong at high coherent light and is related to the effectively excitation of Zeeman split electron levels. The same effect is observed for undoped BSO crystal, but below 530 nm. Therefore, it is expedient to use undoped BSO crystal and operate in 600-700 nm spectral range, where light sources are suitable for fiber-optic application. A construction of magnetic field sensor head is presented. The achieved accuracy of this element is 10^-5 T, with a variation of the output signal within 2 percent over the temperature range 10-40 degrees C.

Experiments on atherosclerotic plaque diagnosis were carried out using laser induced fluorescence. Different excitation wavelengths were tested: 488 nm and 457.9 nm of a c.w. Ar⁺ laser as well as 476 nm and 407 nm of a c.w. Kr⁺ laser. Over 15 samples were examined and several spectra were obtained from each sample. Results were cross- examined with conventional clinical techniques, such as histopathological diagnosis, which showed three main components of the atherosclerotic plaque: fibrous tissue, lipid constituents and calcified plaque. An effort was made to distinguish the composition of the sample from the obtained spectra. Fluorescence spectra corresponding to calcified plaque present their maximum in the area of 530 nm - 550 nm. However, there was not observed a specific wavelength where spectra corresponding to fibrous tissue and lipid constituents present maximum. Full width half maximum of the fluorescence spectra was also measured and the ratio of the fluorescence intensity at 600 nm over the intensity at 576 nm, I(600)/I(576), was calculated.

A compact fiber optic spectrometer has been developed for the identification of arterial tissues. Two methods of laser induced autofluorescence spectra analysis were suggested to strongly distinguish atherosclerotic plaque from normal arterial wall. When the fluorometer is combined with a XeCl excimer angioplasty system it can be capable of guiding the process of safe laser ablation of atherosclerotic occlusions.

The results of the measurement of the penetration of the laser light inside dental configurations are reported. The illumination of the pulp chamber is carried out. The results can be employed in clinical practice for dosage in treatment of periodontal diseases.