Methods of precision laser spectroscopy and optical frequency synthesis are discussed in view of their application in optical frequency standards. The lowest possible uncertainty is expected from a standard based either on a single ion, trapped and laser cooled in a radio-frequency trap, or an ensemble of neutral atoms released from a magneto-optical trap. A relative frequency uncertainty of 2.5 (DOT) 10^-13 has already been demonstrated for a Ca optical frequency standard using the latter concept. Aa novel method of optical frequency synthesis based on femtosecond lasers is also described.

We analyze the Hanle effect on the closed F_g equals 3 yields F_e equals 4 D₂-line transition of ⁸⁵Rb, by both numerical solutions of the optical Bloch equations and by experimental investigations on cell containing rubidium vapor. For laser radiation with linear polarization orthogonal to the applied magnetic field, the Hanle signal is characterized by narrow bright resonances at low laser intensities. A bright resonance Hanle signal is obtained also exciting the rubidium atoms by circularly polarized laser light and scanning a transversely applied magnetic field, at different values of an applied longitudinal magnetic field. We report experimental and numerical evidence of this new bright resonance.

The basic ideas of the 'white-light' laser cooling and trapping are discussed and the applications to atom and ion cooling and trapping are presented. 'White-light' cooling allows one to maximize at the same time both the velocity capture range and the cooling rate. This give the possibility to improve the trapping collection efficiency, to reach lower temperatures in presence of strong heating processes, to cool and trap atoms by involving very narrow transitions from metastable levels. The definition and the realization of 'white' laser sources is presented and the improvements achieved with respect to the use of single mode lasers is demonstrated in the case of fast ions confined in a storage ring and in magneto-optical trapping of neutral atoms.

Production of translatory cold molecules from laser-cooled atomic ensembles is reviewed. Molecules in high vibrational levels of excited potentials are generated usually via photoassociation. For production of cold ground state molecules, up to now no general scheme is known.

A TEA-TEA HF (SF₆:C₃H₈:He) oscillator-amplifier laser system with one common switching element and one common power supply unit was designed. Two different preionization schemes were employed. One using a corona discharge on a glass plate and another one using semiconductor slabs. For both arrangements the improvement of the laser beam characteristics of the TEA HF laser oscillator, such as beam profile and output energy, was investigated. The beam profile is discussed and presented in detail in 2D and 3D figures with the help of a beam analyzer system and the gain measurements for the specific active gas mixture and the specific laser head geometry are given in terms of the small signal gain coefficient g_o and the gain value G parameters.

Experimental investigation of Q-switched Nd:YAG laser, utilizing unstable resonators with variable reflectivity dielectric mirrors is presented. We designed flat-convex and confocal unstable resonator. Gaussian and super-Gaussian variable reflection profiles with various mirror spot sizes are used. Comparison between the used resonator schemes is made by measurement of the following laser parameters: energy extraction, near- and far-field intensity distributions. Output energy of 400 - 450 mJ is obtained for different resonators at repetition frequency up to 5 Hz. The advantages of unstable resonators with variable reflectivity mirrors are demonstrated by efficient frequency conversion of the high power Nd:YAG laser.

We developed a novel type of Q-modulator based on cascaded nonlinear chi-2 processes. The principle of operation is based on the nonlinear reflection, which occurs in second harmonic generation or frequency mixing owning to polarization rotation of the fundamental wave in the nonlinear crystal by intensity- induced phase shift. Dynamics of the generation evolution in laser with nonlinear cascaded polarization mirror (NCPM) using the rate equations has been analyzed. Generation of giant pulses is theoretically obtained. This new method for passive Q-switching has a very large working spectral range (from VIS to NIR) and the lack of absorption losses results in low thermal effects which make it appropriate for passive Q- switching of high average power lasers.

It is shown that a combination of a polarizer, a type II second harmonic generation (SHG) crystal at nearly phase- matched conditions, and a back reflector has pulse shortening and mode-locking capabilities. The latter are due to the intensity dependent change of the polarization state of the fundamental wave by cascade second-order processes in the nonlinear crystal. This change of polarization state causes nonlinear reflection, when the fundamental wave passes back through the polarizer, i.e. the combination of a polarizer a SHG crystal and a dielectric mirror acts for the fundamental wave as a nonlinear mirror, called by us a frequency doubling polarization mirror (FDPM). The dependence of the properties of the FDPM on the nonlinear characteristics and the orientation of the SHG crystal, as well as on the accumulated phase shift between the second harmonic and the fundamental wave within the space between the nonlinear crystal and the back reflector were investigated.

We describe (computer analysis and experimental realization) a developed Nd:YAG laser system, capable of emitting a pair of nanosecond pulses with independently controlled delay and intensity. The output parameters of such a laser in low and high flash lamp pump levels are compared. The possibilities to achieve different temporal distances between the two pulses and different energies per pulse are discussed. The build-up time and levels ratio stability are studied. A method for total output energy optimization is proposed. The behavior of the two-pulse laser output after laser amplification and frequency doubling is discussed. Pure two-pulse Nd:YAG output with pulse distance from 0 to 3 microseconds is demonstrated. The possibility to apply this technique to different laser active media have been discussed as well as the different potential areas for application of a dual pulse laser output.

It is theoretically shown that using saturable absorbers in unstable resonators can lead to large-volume super-Gaussian beams generation under certain conditions. Practical aspects for Q-switched super-Gaussian beam generation are discussed. The method is experimentally improved.

We describe a simple, new technique for producing of nanosecond pulses with rectangular (or triangular) temporal shape and with tunable wavelength. The technique is based on a pumping of a tunable dye laser by pulses with formed rectangular (or triangular) shape, emitted from a standard Nd:YAG (2^-nd harmonic) or Copper-vapor lasers. The pump pulses are formed in a simple electro-optical system. We have shown theoretically that the main problem to reproduce the pump pulse shape in a nanosecond dye laser -- a 'spiking' phenomenon, can be avoided using an appropriate pre-pulse pumping of the dye before the main, formed pump pulse. The experimental check confirms the theoretical predictions.

We describe and analyze an original technique for all-optical and high gain (approximately 10³ - 10⁶) amplification of a periodically modulated (PM) intensity low-power (approximately (mu) W) laser radiation. The amplification is based on the injection locking control in linear laser schemes with homogeneously broadened active medium. The main problem of the injection locking amplifiers is to obtain a linear response to the PM injection. We propose to solve this problem by injecting a second laser beam with a constant power and a slightly different wavelength or orthogonal polarization compared to the injected PM beam.

Our work is based on a model with multidimensional variations of parameters and which includes 7 population equations and two field equations. The physical correspondence is a 7 level Er³⁺ fiber system placed in resonant cavity, and subject to lasing condition. Our project was focused on both time and optic - intrinsic parameters dependencies of the relevant physical quantities. The relevant physical parameters are highlighted. The change of the host material was embedded in a three dimensional variations. Time dependence is also investigated. Our results were consistent physically and in agreement with literature.

The aspects of the optical power density resonator mirrors loaded in dynamically stable resonators at high power operation are discussed. A concept for symmetric multirod resonators is proposed as a way to reduce the on-mirrors power density proportionally to the square of the number of the rods used to obtain the same output power. Two-rods symmetric dynamically stable resonators are investigated theoretically. An optimized for 400 W average power operation at low diffraction limited beams two-rod dynamically stable resonator is designed for purposes of a solid-state laser cutting system.

A self-seeded coupled-cavity pulsed tunable laser using a novel competitive active mirror (CAM) is reported. The operation of CAM is demonstrated and studied experimentally in the case of pulsed dye laser, pumped by a frequency-doubled Nd:YAG laser, with a Fizeau wedge as a spectral selector. The results obtained reveal that both the conversion efficiency and output energy of the CAM laser are considerably higher as compared to the ones achieved in the case of pure selective laser under equivalent pumping conditions. Appearance of a spectral background is naturally prevented in the CAM laser, regardless of pumping energy fluctuations, cavity misalignments, and unperfect temporal synchronization.

A sliding-discharge directly-excited pulsed atomic fluorine laser was realized for the first time and investigated experimentally. The atomic fluorine was produced by dissociation of F₂ in a He:F₂ mixture by a fast-pulsed electrical discharge. The optimum active mixture was found to be 1.6% F₂ and 98.4% He, at a total pressure of 90 mbar. A doubling electrical circuit was used for sliding discharge excitation. The laser performance characteristics (the voltage and laser pulses, output energy and gas mixtures) were studied. The laser spectrum consisted of three lines at 703.7 nm (3p²P⁰_3/2 yields 3s²P⁰_3/2) 712.8 nm (3p²P⁰_1/2 yields 3s²P_1/2) and 731.1 nm (3p²S⁰_1/2 yields 3s²P_1/2). The output power of the laser was higher than 1 kW and the pulse duration (at FWHM) measured was about 30 ns.

For atomic species of molybdenum extracted by pulsed laser deposition and isolated in Ar matrix at 11 K the photoluminescence spectra in the range from 360 nm to 620 nm are recorded under excitation of the z⁷P absorption triplet by the 355 nm laser pulses. Emission lines at 496.7, 548.1 and 602.0 nm are assigned to atomic transitions from Mo b⁵D, a⁵P and a⁵G to the ground a⁷S state and the slightly red shifted peaks at 501.6, 550.3 and 603.9 nm are ascribed to atoms at different matrix sites due to preparation. Values of the stimulated emission cross section and of the optical gain coefficient obtained from experiment for the Mo/Ar solid lie in the range of (1 divided by 25)X 10^-20 cm² and up to 0.29 cm^-1, respectively and are comparable with those of other three- level laser systems.

We report the experimental results of the power-related frequency shift and the power-shift coefficient of an iodine- stabilized He-Ne laser with two methods of power variation: misalignment of the laser cavity and change of the polarization orientation between iodine cell and gain tube. A short internal-mirrors He-Ne laser PLL offset-locked to an iodine-stabilized He-Ne laser was the reference laser. The experimental data were processed following three methods: the standard matrix method, the diagonal method and the reference line method.

The influence of the ³He isotope as a buffer gas on the operating characteristics of the He-Ne and He-Kr hollow cathode lasers is studied. A comparison of the laser output power on the NeI 1.15 micrometer line (2s₂ - 2p₄ transition) and KrII 469.4 nm line (6s ⁴P_5/2 - 5p ⁴D_7/2 transition) in ³He-noble gas and ⁴He- noble gas mixtures is made. An increase of 4 times in the case of ³He-Ne gas mixture and of 33% in the case ³He-Kr gas mixture is observed. The plasma kinetics is analyzed and it is shown that the observed increase of the laser parameters is due to the following changes in particle kinetics: (1) increased rate constant for the excitation transfer reaction; (2) increased density of the He (2 ³S₁) metastable atoms; (3) decreased population rate of the NeI lower laser level 2p₄; (4) decreased density of the Ne (1s₃, 1s₅) metastable atoms and (5) increased density of the Kr ground state ions. The main reasons for that are the higher mean relative velocity of the colliding particles and the higher rate of electron cooling in ³He-noble gas plasma. Peak powers of 10 W and 1.5 W and small signal gains of 85%/m and 64%/m are measured for the blue and violet KrII lines, respectively, from 21 cm active length.

For SiO₂ glass samples doped with Cu⁺ ions at 150 - 500 ppm and prepared by the sol-gel method the absorption, excitation and emission spectra are recorded. Due to excitation in the broad absorption band (250 - 350 nm) a strong luminescence at 540 nm and of FWHM equals 100 nm is observed. Dependencies of the spectral characteristics of this emission on the excitation indicate on the ASE and a possible lasing potential.

The investigation deals with analysis of antireflection coatings of two transparent materials with high (H) and low (L) refractive index for two wavelengths 1.30 micrometer and 1.55 micrometer in the near IR on glass/silica substrates. The results are obtained by numerical optimization approach which algorithms are realized using programming language DELPHI. The initial structures of LHL three-layer and LHLH four-layer coating (optimized for both wavelengths) are modifications of double-layer antireflection coating for one wavelength 1.4 micrometer. It is shown that the highest transmittance near 1.30 and 1.55 micrometer (practically equal to 100%) shows LHLH four-layer coating structure. The total physical and optical thickness of optimized LHLH four-layer coating is smaller than corresponding value for optimized LHL three-layer coating. Four-layer LHLH coating is more stable with respect to small n and d variations and corresponding transmittance changes are less than in case of LHL three-layer coating.

In the present work we present a Fizeau wavemeter built on the base of uncoated optical flats for cw lasers. Testing of the wavemeter is made for a 1-mm thick wedge with apex angle of 3 min. The accuracy of the wavemeter is 5 X 10^-6. As a second task we study the possibility to use a wedge with reflecting coatings for enhancement of the interference pattern. The main advantage of such a wedge is the substantial rise in the peak intensity of the reflected fringes (two orders of magnitude larger intensity for 50% reflectivity of the coatings compared with the case of uncoated surfaces). The main drawback of using coated surfaces is that they create asymmetric fringes with many subfringes. We show by computer simulation that detection of the interference pattern in the zero-shear plane ensures symmetric fringes and high-accuracy wavelength estimates up to 50% reflectivity of the wedge coatings.

A two element magneto-optical trap (MOT) in standard configuration for Na and ⁷Li or ⁶Li is used to cool and trap Na and one Li isotope simultaneously or separately. The metal background vapor out of which the atoms are trapped comes from dispensers. The two atom clouds can be slightly shifted what makes it easy to overlap them. The number and density of the clouds were determined and the temperature measured roughly. The mutual influence of the clouds was investigated and turned out to be smaller than the noise. Preliminary experiments working towards the production of heteronuclear cold molecules by photoassociation were performed, showing the well known production of Na₂ long- range molecules. Additionally, the photoionization cross- section was determined by ionizing cold atoms in the excited state by UV-laser light. The results are in reasonable agreement with data obtained elsewhere using synchrotron radiation.

An experimental study of electromagnetically induced two- photon transparency (EITT) in rubidium atomic vapor at room temperature is presented. A four level system is considered, involving the two-photon absorption process 5S_1/2 to 8S_1/2 via an intermediate state 5P_3/2, and the single- photon control process 5P_3/2 to 5D_5/2. A controlling pump laser beam is employed to coherently couple the 5P_3/2 and 5D_5/2 states, thus producing two dressed intermediate states, which give rise to destructive interference in the two-photon transition. Fluorescence from 8S_1/2 to 5P_1/2 is used to monitor the 5S_1/2(Fequals3) to 8S_1/2(Fequals3) two-photon absorption. An induced two-photon transparency of about 80% has been obtained at resonance; the experimental results are in good agreement with the general theory of Agarwal, when the appropriate spectroscopic parameters are employed.

In this communication we present experimental investigation of coherent effects at Zeeman sublevels of hyperfine levels of Rb in dependence on the polarization of the pumping laser field in order to obtain more complete information about the dark and bright CPT resonances. The coherent effects are examined in Hanle effect configuration, exciting Rb vapor cell with a single-frequency diode laser. By means of phase-sensitive detection (PSD) the amplitude and sign of the CPT resonances are registered in the vicinity of the Rb D₁ and D₂ lines. It is shown that the sign of the CPT resonances changes when the polarization of the exciting beam changes. Theoretical calculations are performed for the population losses of the given transition in order to clarify the observed experimental results.

Dark States for Rubidium 85 have been obtained in glass cells containing saturated vapors of natural Rubidium at room temperature. The two radiation, which are required to induce the dark states, have been generated by modulating the light emission of a laser diode, tuned at the S-P optical transition. A measurement of the energy difference between the hyperfine states F equals 2 and F equals 3 of 5S_1/2 is performed by an optical way. By using simultaneously two laser diodes, one tuned at the D₁ transition and the other at the D₂, we have generated two different Dark States. Interference between the two dark states prepared on the same place has been studied by changing the phase of the D₁ and D₂ excitations. A new way to modulate laser beam intensity is shown.

A simple theoretical description is proposed aiming at a qualitative explanation of the observed in ¹¹ dependences of the fluorescence from the resonant Rb levels excited by a single frequency diode laser on the magnetic field, when Hanle effect configuration of the experiment is used. The components of the statistical tensor for population and longitudinal alignment are calculated by iteration method up to fourth order terms. The spontaneous emission transfer influence is taken into account. A good qualitative agrement between calculated and experimentally observed resonances is obtained.

A nonlinear Hanle effect on the 2³ P yields 3³ D HeI transition has been investigated. The experiment was performed in way to eliminate from the signal the contribution of the population dependence on the magnetic field. The shapes and widths of the Hanle curves were analyzed for different saturation parameters. The signal arises from two nonresolved He transitions-the 2³P₂ yields3³D₂ and the 2³P₂ yields 3³D₃. Cross-correlation analysis was suggested to analyze the contribution of a low intensity optical signal to the main experimental curve.

The saturated absorption spectrum of D2 line in Cs was investigated using two diode lasers emitting at 852 nm. It was obtained in a 5 cm long Cs cell at room temperature. The frequency scale was calibrated using the beat note signal from a fast photodetector on which the two laser beams were combined. In order to eliminate the effect of the reference laser frequency drift, a two-laser beam optical arrangement producing the saturated absorption was used. A simple model giving the number of observed peaks and the frequency intervals between them was developed. The two spectra corresponding to the two ground state components of Cs were fitted using a Lorentz profile as a model function and the obtained frequency intervals were compared with the Cs atom hyperfine splittings.

We analyze the picosecond pulse propagation in a fiber communication line with periodically inserted semiconductor optical amplifiers in the framework of averaged soliton concept. It is numerically shown that in such line the pulses similar to the dissipative optical solitons observed earlier in the non-linear two-level medium can appear.

Propagation of an intense femtosecond light pulses is investigated by a numerical model which provides the full spatial and temporal description. This is a simulation of pump and probe experiment where the probe pulse is affected by the presence of the pump pulse. Deviation of the plane-wave approximation and its correction to Gaussian beams is studied under variation of several sample parameters. The results give a view to some limitations of use of the approximation.

It is well known that the nonlinear Schrodinger equation (GNLSE) has bistable soliton -- like solutions for a nonlinear form of the functions f(E²). Such kind of solitary bistable waves doesn't appear in the case of the Kerr -- like nonlinearities of the medium. The stability of these solitary bistable waves was later on studied by Enns et al., who have established, by numerical simulations, the soliton- like nature of these solutions for a certain category of functions f(E²). Our numerical simulations, based on similar mathematical models are presented in this work. By comparing our results to those obtained by Enns, Rangnekar and Avity, as well as to Ikeda's results, who have used a similar model, we have obtained results which are in good agreement with theirs, for small values of A. For larger values of A, the system doesn't return to period 1, but continues to have a chaotic behavior. Such kind of bistable soliton solutions for the GNLSE equation is very important for several applications, such as: optical fiber communications, optical switching, bistable optical devices, etc.

Various types of dark optical beams with respect to their phase dislocation are discussed and their propagation dynamics is analyzed. On the basis of numerical results 1D and 2D optical couplers are proposed. The respective energy efficiencies for each of the output channels are estimated. Multiple charged optical vortices and their topological instability are presented. Through a proper type of perturbation applied to these vortices they could be split into several sub-beams, thus giving the opportunity of proposing all-optical branching schemes. Two output channel distribution schemes for such an optical brancher are discussed.

Theoretical and experimental results on optical ring dark solitary waves are presented, emphasizing the interplay between initial dark beam contrast, phase-shift magnitude, background-beam intensity and saturation of the nonlinearity. An enhanced RDSW transverse dynamics originating in the interaction with a second coaxial dark beam is analyzed theoretically in a good agreement with the experiment. The results may open the way to construct a parallel all-optical three-position radial switch.

Multiple-charged optical vortex solitons (OVSs) are generated in a thermal nonlinear medium with saturation. The respective soliton constants are found to be linearly proportional to the topological charges. The linear stability analysis and the numerical simulations indicate a rich variety of instability scenaria depending on the type of perturbation. The saturation of the nonlinearity is shown to be able to slow down the decay of multiple charged dark beams at an intermediate evolution stage and to prevent their ultimate decay into charge-one OVSs. This concept is experimentally verified by the experimental observation of a partial decay of a triple- charged optical vortex beam.

In this work we present nondestructive measurements of the optical parameters and propagation losses of multimode planar H_xLi_1-xNbO₃ waveguides using m-line spectroscopy. The dependence of the attenuation coefficient on the effective refractive index was investigated for z- and y-cut samples. Theoretical modeling of the experimental data revealed that the main loss mechanism in z-cut waveguides is the surface scattering, while in y-cuts the mode conversion dominates.

Laser photodetachment measurements of the negative ion density in an oxygen currentless plasma are reported. For this experiments a DC gas discharge tube with a coaxial nickel sectional cathode (diameter 5.10^-2 m) and a grid anode (diameter 2.10^-2 m and length 0.2 m) is used. The measurements are made in pure oxygen at gas pressure 109 Pa and discharge current 40 - 80 mA. Inside the anode region the reduced electrical field E/N_g is near zero (N_g is the gas density). The currentless plasma is formed by plasma particles moving from the negative glow into the cavity inside the anode. The negative charged particles dominantly are negative ions with Maxwellian energy distribution. The negative ion density is measured on the axis in the center of the discharge tube by measurement of the relative absorption of the laser power. A 5 mW 785 nm diode laser is used for the measurements. The obtained values of the oxygen negative ion density at gas pressure 109 Pa and 80 mA are approximately 10^-13 cm^-3 and are in good agreement with the values obtained by second derivative Langmuir probe measurements.

Negative hydrogen ion concentration in (Ne+H₂) positive column glow discharge has been investigated. It is measured by optogalvanic method. The populations of neon metastable 1s levels and neon 2p and 2s blocks of levels and concentrations of Ne⁺, H, H⁺, H₂⁺, H^- in this discharge are estimated, including vibrational kinetics.

Laser induced Galvanic Signals (LIGS) were observed in a Se- buffer gas hollow cathode (HC) discharge irradiated by He- Se⁺ or cw dye lasers. Radial and current dependences were studied. A similarity of the radial dependences for the two buffer gases He and Ne and maximum in the current dependences are registered. The possible mechanisms which form GS responses in Se HC discharge are discussed.

Some interesting results on the laser ionization of sodium in thermionic diode based on 3s - 3p resonance saturation (LIBORS) with excimer pumped dye laser are reported. The results are compared with two-color/two-photon ionization where the excimer photon at 308 nm is used as the 2nd photon.

Light induced atomic desorption (LIAD) is an impressive manifestation of a new class of phenomena involving alkali atoms, dielectric films and light. LIAD consists of a huge emission of alkali atoms (experimentally proved for sodium, potassium, rubidium and cesium) from siloxane films when illuminated by laser or ordinary light. Most of the experiments have been performed in glass cells suitably coated by a thin film (of the order of 10 micrometer) either of poly - (dimethylsiloxane) (PDMS), a polymer, or of octamethylcyclotetrasiloxane (OCT), a crown molecule. LIAD is a combination of two processes: direct photo-desorption from the surface and diffusion within the siloxane layer. The photo-desorbed atoms are replaced by fresh atoms diffusing to the surface. Moreover, from the experimental data it comes out that the desorbing light increases atomic diffusion and hence the diffusion coefficient. To our knowledge this is the first time that such an effect is clearly observed, measured and discussed: LIAD represents a new class of photo-effects characterized by two simultaneous phenomena due to the light: surface desorption and fastened bulk diffusion.

Light-induced absorption in pure B₁₂TiO₂₀ crystal and crystals doped with Nd, Mo, W, and V was investigated using the pump-probe method. Q-switched frequency-doubled (532 nm) YAG:Nd laser with pulse duration approximately 20 ns was applied for sample irradiation. Investigation of pump-induced transmission was carried out by means of a tunable dye laser radiation at (lambda) ₁ equals 568 nm and (lambda) ₂ equals 698 nm. The dependence of the light-induced absorption coefficient on the pump beam intensity and probe wavelengths was determined. The two-center model was used to explain the observed results.

Here we report the proposed by us concept for monitoring the atmospheric and Earth Hg and Pb pollution by means of Intracavity Laser Spectroscopy (ILS). The concept profits from the extremely high sensitivity of the ILS dye laser registration by preliminary excitation of the Hg(Pb) atoms to a suitable level to induce absorption at the analytical transition corresponding to the second dye laser emission spectrum. A theoretical proof is given on the possibility for two-step optical excitation from the ground state level.

The hydrogen bonding in water and 2M aqueous solutions of NaCH₃COO, (CH₃)₄NCl, NaCl and NaCSN was studied by Raman spectroscopy of the vibrationally decoupled O-D stretching band of water. The isotropic O-D stretching spectra were modeled by means of Gibbs' statistical ensembles of hydrogen bonded oscillators. The thermodynamical parameters of the ensembles were estimated. They were related with properties of the hydrogen bond network in water. It was revealed that the salts break the structure of water reducing the strength of hydrogen bonding. According to their influence on the strength of hydrogen bonding the salts can be arranged in a series similar to the Hofmeister series of salts.

In this work an automatic operating prototype of a laser refractometer is described. The device consists of a refractometric block, where the refractive index (RI) of liquids is detected according to modified prism method, build- in interferometer for determination of the angle of rotation, which use the same laser and system for contact measurement and control of the liquid temperature with an accuracy of 0.3 degrees Celsius. The automatization of the measurement avoid the subjective related errors. The construction permits the utilization of various lasers as light sources. The achieved accuracy of about 1.10^-4 allows applications of the refractometer in various kinds of problems as optical constant determination, concentration measurements, purity control, in situ biomedicine diagnostic and etc.

We present an improved version of the Inverted Perturbation Approach (IPA) method for construction of potential energy curves of ¹(Sigma) and ¹II stats of diatomic molecules directly from the experimental data. Using the constructed IPA potential one can reproduce the experimental energy levels within the given accuracy of measurement. We describe application of the method to a case of double minimum potential where the traditional RKR method fails.

Studies of the radiative lifetimes of some of the Beutler (formula available in paper) states of the mercury atom have allowed us to propose an inversion population mechanism for some of the laser actions observed previously. Most of the laser transitions in HgI are in the IR spectral region and few of them are connected with the Beutler states. We focused on the (formula available in paper) ((lambda) equals 5.88(mu) ) transition. A qualitative analysis of this laser transition is proposed.

LiNbO₃ and LiTaO₃ are commonly used ferroelectric crystal materials. Since the first reports of successful single domain crystal growth in 1965, these materials have found increasing use in optoelectronics, laser systems, Q- switching and frequency conversion, holographic data storage, surface acoustic wave devices, integrated optics and modulator use, and most recently, microwave telecommunications. In single domain format these ferroelectrics are photorefractive, pyroelectric and piezoelectric, and possess usefully large nonlinear optical and electro-optical coefficients. If domain engineering or micron/nano-scale bulk or surface modification is performed however, greater functionality is introduced, leading to additional uses such as phase-matched frequency conversion, grating and photonic structures, and the recently proposed use in MEMS and MOEMS devices. We discuss here a range of techniques for domain engineering and domain selective etching, as well as the use of light in poling and etching modification, and illustrate this potential with several devices that we have constructed by these routes.

In this paper we describe the use of pulsed laser deposition (PLD) for the growth of thin film V_xO_y, NdNiO3 and Pb(Mg_1/3Nb_2/3)O₃. We begin by briefly describing our growth system. By showing case studies of the three materials systems we identify some important aspects and conditions that we believe are of crucial importance to oxide film growth in general.

Highly nitrogenated CN_x films were created by pulsed laser deposition (PLD), combined with radiofrequency (RF) and hollow cathode (HC) discharges. The RF discharge was held between two electrodes situated parallel to plasma plume from a graphite target. In PLD combined with HC discharges an one of the RF electrodes was used to supply nitrogen on the substrate. The N/C ratio higher than 1 was measured. Deposition set-up and its various modifications and an accuracy of composition measurement of CN_x layers by WDX and RBS methods are discussed.

Laser materials processing has been used in the industry for drilling, cutting, welding, scribing, and etc. In most of the scientific papers, the authors assume that the laser energy imparted to the material is transformed into heat. This induces phase transformation as melting, fusion, sublimation, or vaporization. It is known that the atoms and ions are produced in high density plasma plume due to laser irradiation. In order to clarify microscopically the ablation and vaporization phenomena the material must be regarded as an aggregate of atoms or molecules, not as a continuum. It is difficult to observe the processing phenomena experimentally, because it occurs in very small region and for a very short time interval. Consequently, the phenomena must be elucidated by theoretical analyses or simulation to some extent. Laser ablation of nickel has been investigated by molecular dynamics simulation. The process of determination of equilibrium in the atomic system was examined as a first stage of simulation. The influence of the laser energy fluence on the process of ablation was studied. The threshold for ablation, values of the velocities of the ablated atoms were obtained.

The development of a viable HTS coated conductor technology requires the deposition of biaxially aligned Y₁Ba₂Cu₃CuO_7-y (YBCO) layers onto flexible metallic substrates. Using pulsed laser deposition (PLD) YBCO/CeO₂/YSZ heterostructures have been deposited onto biaxially textured Ni and Ni-alloy substrates. The influence of the critical processing parameters on the texture is investigated and some of the issues involved in the deposition of heterostructures are discussed. The texture in the layers has been characterized using X-ray Diffraction (XRD). The as deposited architecture shows YBCO layers with biaxial alignment with XRD (omega) and (phi) scans having best FWHM values of 3.5 degrees and 11 degrees respectively. The growth of the layers has also been studied using Atomic Force Microscopy. Tc at 90 K with sharp transition ((Delta) equals 2K) have been measured.

We report a theoretical and experimental comprehensive study of the synthesis of TiN by RPLD from Ti targets in (0.2 - 50) Pa nitrogen. We used an UV XeCl* excimer laser source ((lambda) equals 308 nm, (tau) _FWHM<EQ 30 ns). The deposited structures were characterized by electron microscopy, XPS and RBS. We observed a tight interval of the ambient gas pressure of (0.7 - 7) Pa within we deposited stoichiometric, polycrystalline TiN films. The theoretical analysis was performed with a numerical multifluid code using the 1D heat- conduction equation. The transit of the ablated material from target to collector was treated by a Monte-Carlo method. Finally, the thickness profile of the deposited films was predicted. The obtained results are in good accordance with experimental measurements.

The ferroelectric Pb_1-xLa_x(Zr_yTi_z)_{(1- x/4})O₃ (PLZT) (x equals 0.09, y equals 0.65, z equals 0.35) optical waveguiding thin films have been prepared on fused silica, (001) quartz, (0001) sapphire and CeO₂ coated (11 02) sapphire substrates by pulsed laser deposition. X-ray 20 scans showed that the films are amorphous, highly pyrochlore <110> and highly <110> pseudocubic perovskite textured. The chemical composition of the films was determined by WDX and the influence of oxygen partial pressure on the lead content was observed. The optical waveguiding properties of the films were characterized using a rutile prism coupling method. The distinct m-lines of the guided TE and TM modes of the films have been observed. The refractive index measured by m-line technique reached value about 2.2 at 633 nm wavelength, which is close to the PLZT bulk value. The films have transmittance of about 70% at the wavelength 400 nm.

Thin films of YBa₂Cu₃O_7-x have been obtained on NdGaO₃ substrate by pulsed laser deposition with an excimer KrF* ((lambda) equals 248 nm, (tau) _{FWHM>= 20 ns} laser source from a stoichiometric target. In the present paper we report details of the technology of pulsed laser deposition of high-temperature superconductor thin films, substrates' requirements and high-temperature superconductor thin film characterization. The study of some parameters' intercorrelations for optimization of the technology of the pulsed laser deposition of high-temperature superconductor thin films is also analyzed. Moreover, the contacting technology and techniques of characterization are described.

We investigated the effect of substrate orientation and film thickness on the microstructure and magnetic properties of Sr- ferrite films grown on (0001) and 1102) sapphire substrates by pulsed laser deposition (PLD). The films grown on (1102) sapphire displayed a presence of various magnetic phases, including SrFe₁₂O₁₉ Fe₂O₃ and Fe₃O₄. The single hexaferrite phase was obtained in GIXRD at 1 degree and 5 degree for the thicker film. The structure measurements showed that all films on (0001) sapphire were single-phase c- axis oriented hexaferrites. The highest in-plane coercive force of 2.5 kOe was detected for the thicker film grown on (1102) sapphire. These films exhibit the highest in-plane squareness. The saturation magnetization of the films on (0001) sapphire rose when the film thickness was reduced.

Crystalline hydroxyapatite (HA) thin films grown on metallic substrates is the best choice for bone restoration. This is due to the good biological compatibility of the hydroxyapatite material combined with the good mechanical characteristics of the substrates. We deposit HA thin films by Pulsed Laser Deposition (PLD) in vacuum at room temperature using a KrF* excimer laser ((lambda) equals 248 nm, (tau) _FWHM >= 20 ns). The depositions were performed directly on Ti-5Al-2.5Fe or on substrates previously coated with a TiN buffer layer. The HA deposited structures were characterized by complementary techniques: GIXRD, SEM, TEM, SAED, EDS and nanoindentation. Properties of the HA films grown with and without the TiN buffer were discussed in term of microstructure and mechanical behavior. The films with interlayer preserve the stoichiometry, are completely recrystallized and present better mechanical characteristics as compared with those without buffer.

Thin films (250 nm - 1200 nm) of cubic Y₃Fe₅O₁₂ (YIG) were deposited on fused silica and monocrystal Y₃Al₅O₁₂ (YAG) 100 substrates by spray pyrolysis (using ethylene glycol solutions of Y-Fe(III)-citric complexes) and additionally annealed at 950 degrees Celsius in static air for 2 h. The films were afterwards irradiated by a free-running Nd-YAG laser (pulse energy 650 mJ, pulse duration 700 microseconds, energy density 100 mJ/cm²) whose onset was synchronized with that of a magnetic field pulse of nearly-square shape (magnetic induction 0.5 T, pulse duration 900 microsecond). The samples were placed normally to the direction of the magnetic field. The temperature reached at the film surface was estimated to be as high as the melting point, considerably higher than the Curie temperature. The laser-magnetic field treatment causes: a sharp weakening of the YIG/YAG films texturation, highly textured before that treatment; an increase of the crystallites size; change in the phase composition of the YIG/silica films; an increase of the magnetization by more than 45%; an increase (in the case of YIG/silica) and decrease (in the case of YIG/YAG) of the coercive force.

A locally developed 200 W CO₂ laser with multi-mode output was used to study the surface hardening of different steels. Maximum hardness was achieved in the region where the microstructure was transformed to martensite. The microhardness was found to increase with carbon content. In a new experiment, AISI 1045 steel specimen was first annealed and then treated with laser. The microhardness of annealed samples was found to be higher than the untreated samples. Preliminary results are presented.

Cold-rolled rimming steel has been surfacely treated by pulse Nd:YAG laser. The modification of structure parameters has been analyzed by X-ray diffraction. It has been found that the main consequences of the laser treatment are surface oxidation and formation of significant residual macrostresses.

Photoanisotropic materials make it possible to produce novel optical elements with specific polarization characteristics. Good examples are polarization holographic gratings (PHG) recorded with two waves with orthogonal circular polarizations. It has been shown that these PHG are of great interest for polarimetry as they allow for an easy and fast measurement of the Stokes parameter S₃, including its spectral dependence. Here we discuss in details the polarization characteristics of PHG recorded in high-efficient photoanisotropic materials. It has been taken into consideration that due to the nonzero recording angle the real interference pattern is modulated not only by polarization, but also by intensity. This modifies the final modulation of the photoinduced anisotropic changes in the optical constants of the material and hence, the polarization characteristics of the produced gratings. The differences between the 'ideal' and a real PHG depend on the recording angle and on the photoresponse of the recording material, especially on the presence of scalar component in the photoinduced changes of the refractive index n. These polarization characteristics have also been observed experimentally.

A new method for restoration of ceramic surfaces, based on laser ablation of impurities has been developed. Optical pulses generated by Nd:YAG laser are used to remove a high absorbing layer (fungi) from the surface of a lower absorbing ceramic substrate. Two regimes of operation have been employed: Q-switched mode and free running mode. Analysis suggests that Q-switched mode of operation is the most efficient for cleaning processes. Densities of energy 1.60 - 1.90 J/cm² at the fundamental wave and pulse duration 10 ns are the typical values for removing of impurities of fungi from ceramic surfaces. The second, third and forth harmonics of the Nd:YAG laser have been also used for optimization of the process of laser restoration. The absence of structural changes of the ceramics surface after the process of laser cleaning has been observed by X-ray analysis. The used ceramic substrate is dated 5000 BC- a part of the excavations near Durankulak.

Photoinduced changes in the structure of amorphous chalcogenide films reflect in their optical transmission as photodarkening (PD) or photobleaching (PB). As a rule As- chalcogenides photodarken while Ge-chalcogenides photobleach when illuminated by band-gap light. Our previous investigations have shown that in Ge_xAs_40-xS₆₀ films PD and PB depend on the prevalence of the As- or Ge- content, respectively. In the present work we show for the first time that the appearance of PB or PD in the Ge-As-S films depends not only on the composition, but also on the characteristics of the irradiation source. Pulsed and CW lasers as well as HBO 500 lamp were used to specify the necessary experimental conditions. Possible explanations of the differences in the light effects are discussed.

In this paper the possibility of applying the new-generation high-power CuBr laser in precision micromachinging is presented. Several industrial applications of the presented CuBR laser set-up are shown.

Until now, all studies were done over the semiconductor glasses doped with CdS_xSe_1-x, in which the microcrystallite phase was grown into a vitreous silica matrix. Our study was made as for growing microcrystallites of CdS_xSe_1-x into a vitreous aluminophosphate matrix. In the first step, the samples of semiconductor glass were obtained by melting the raw materials batch and then by adding sulphur selenium and cadmium into the molten glass. In the second step, the resulted glass was annealed in order to bring about the microcrystallite nucleation and growing process. Both linear and non-linear optical properties are deeply influenced by the microcrystallite size, which, in its turn is determined by the duration and temperature of the annealing treatment. By means of a spectrophotometer (SPECORD M-42), were drawn absorption, transmission and fluorescence spectra, in visible domain. From the shape and the absorption edge of these spectra, we are able to characterize the microcrystallite growing process. From these spectra it can be observed a shift of the absorption edge to red which depends on the microcrystallite size.

The mechanism of laser beam and tissue interaction is governed by the technical characteristics of the laser beam and the optical properties of the tissue. The therapeutic laser wavelength, pulse duration and beam quality, as well as the laser radiation delivery systems, the ablation mechanisms and the diagnostic techniques to monitor a surgical process are studied in this work. Advanced therapeutic and diagnostic techniques, such as integrating sphere, atomic force microscopy and beam profiling are used in the experimental study. In vitro experiments on tissue, laser ablation and diagnosis using laser induced fluorescence are performed. Finally, in vivo animal trials of an endoscopic/laparoscopic laser prototype are realized, in the framework of the appropriate protocols.

Volume-pressure plots of human arteries can be revealed in vivo, in finger arterioles. To get such plots, we recorded the arterial blood pressure noninvasively by applying a standard method, and detected a signal proportional to the blood volume by using a diode laser. The interest comes from the utility of such topics for diagnostic purpose. One laser beam is focused on the soft portion of the middle phalanx of a finger. The laser beam penetrates the skin and is the blood volume. Such a volume pulses according to the blood pressure. At the finger a small cuff is applied and we control the transmural pressure by inflating and deflating the cuff. The laser operates through small holes in the cuff. The photodiode is inserted into the cuff. Despite of the arbitrary units obtained for the volumes (volume signal is not calibrated) the pattern of the function can be studied and analyzed. By simple mathematical elaboration, the 'relative' compliance of the system can be obtained. At the moment we got data from 5 subjects, and computed the pressure-volume curves and their parameters. The function obtained is highly nonlinear, and a phase shift between volume and pressure is documented as well as hysteresys effects. The study supports future developments of the method in order to calibrate the response and to get a plot of both the static and the dynamic Young modulus.

Excimer laser refractive surgery used in Ophthalmology in order to treat the human eye refraction problems has been performed over 10 years around the world. However a systematic approach of the physical phenomena and especially of the absorption on the cornea during the laser treatment is missing in the literature and the doctors are usually using empiric nomograms in order to achieve good results. The theoretical approach is difficult because of the complexity of the phenomena interconnected each to the others. The UV excimer laser beam used to controllably ablate the cornea is highly absorbed in the air and also is supplementary absorbed in the plume generated almost instantaneous as consequence of the ablation on the cornea. Because of this non-linear proces the energy of the laser beam delivered to the eye must be calibrated before each intervention on a patient. The purpose of the present work is to develop a mathematical model of the excimer laser absorption on PMMA and on human cornea based on a new physical notion, the Volume Luminance. The Volume Luminance is defined as volume density of the intensity of laser radiation. A brief theory of the Volume Luminance is also presented.

The purpose of this paper is to develop an application that allows an image enhancement to prepare it for an automatic processing. In this way it could be used to establish a computer aided recognition of radiological, echographical and microscopical images.

Last years, lasers' applications in medicine and biology were fully enriched by using computer facilities. Our studies were focused on the nonlinear behavior of some substances important for the living matter, as for example fatty acids and their mixtures with cholesterol and some drugs. The experimental data were computer processed and some computer models of the phenomena were built.

In the present report we draw attention to the phenomenon of laser-induced photodissociation of oxyhemoglobin in cutaneous blood vessels as an important factor in biostimulating and therapeutic action of low energy laser radiation. Calculations of absorption efficiency of laser radiation both by oxyhemoglobin and carbon monoxide hemoglobin were carried out by a computer simulation using Kubelka-Munk model of tissue. It has been shown that the absorption of the oxyhemoglobin in the visible region corresponding to the Q-band of absorption spectra possesses a relatively high selectivity. The obtained results are discussed in terms of developing new methods for wound healing, as well as for carbon monoacid poisoning. Some aspects of the laser-induced photodissociation of oxyhemoglobin complexes are discussed in view of its practical use for developing new diagnostic methods. An attractive way to use this phenomenon is monitoring of local concentrations of oxygen by laser light irradiation.

Monte-Carlo simulations of the light diffusive reflectance from semi-infinite turbid media were performed in order to study the possibility for a stationary diagnostic of biological tissues. Initially the intensity distribution of the diffusively reflected photons as a function of the separation from the light source was calculated for a wide range of absorption and scattering coefficients. The typical maximum in the radial distribution of the intensity was detected. Analyzing those results a relation between the intensity maximum position and the scattering coefficient was observed for all the cases studied. Suggesting that the relationship mentioned could be concludable for an estimation of the scattering coefficient of the tissue an additional study of the angular distribution of the diffusively reflected photons was also made. As a result the applicability of an optical fiber light probe for collection of the photons was discussed. Finally, it was concluded that the steady-state intensity dependence of the diffusively reflected photons on the separation from the light source could be applicable for biologic tissue diagnostics.

In the present work some results of the comparative measurements of the tooth whitening effect using a bleaching agent activated by Ar⁺ (emitting at 488 nm) and CuBr (emitting at 510 nm) lasers are reported. It is shown that the whitening effect is observed in both cases. Some of the peculiarities in application of CuBr laser in the field of aesthetic dentistry are discussed, as well as the possibility to replace the more expensive Ar⁺ laser. In order to ensure reliable results from a light-chemical treatment of the teeth, as spectroscopy method has been developed and applied. The method is based on the analysis of laser-induced fluorescence spectra of the teeth with different coloring.

The aim of this study was to perform a preliminary evaluation of the diagnostic potential of noninvasive laser-induced autofluorescence spectroscopy (LIAFS) for human skin in vivo. The autofluorescence characterization of tissue relies on different spectral properties of tissue. It was demonstrated a differentiation between normal skin and skin with vitaligo. In our experimental investigation of the autofluorescence spectrum of human skin in vivo a nitrogen laser with excitation wavelength 337 nm was used. Two fluorescence bands were observed at 440 and 490 nm, these were attributed to reduced nicotinamide adenine dinucleotide (NADH) and collagen. The intensity of the NADH emission band was markedly reduced in the skin with vitaligo compared with the normal skin, which could indicate different redox conditions in skin with vitaligo. The autofluorescence spectrum of human skin depends on the main internal absorbers, which are blood and melanin. In this study was described the effect caused by melanin content on the shape of the autofluorescence spectrum of human skin. Human skin fluorescence spectrum might provide dermatologists with important information and such investigations are successfully used now in skin disease diagnostics, in investigation of the environmental factor impact or for evaluation of treatment efficiency. The goal of this work is optimization of detection and diagnosis of hollow organs and skin.

A laser laboratory prototype for laparoscopic, endoscopic or angioplastic surgery was developed, incorporating an Er:YAG laser as the therapeutic tool in endoscopic/laparoscopic surgery and angioplasty and a N₂ laser induced fluorescence system in order to monitor the surgical process. Additionally, a laser radiation transmission system with waveguides and fibers was developed, to transmit the laser radiation, through an endoscope or laparoscope. The system was used in in vivo animal trials, giving promising results for the application of the device in semi-operative applications, in combination with systems of improved endoscopic imaging.

The determination of the tissue optical parameters and the study of light propagation in multicomponent tissues is an important tool for real time laser treatment dosimetry and non-invasive laser diagnostics. The purpose of this work was the evaluation of a small portable spectrophotometry system, for non-invasive laser dosimetry, as compared to a more sophisticated, tabletop, spectroscopic system. The small portable system consists of an optical spectrum analyzer, an oscilloscope and appropriate fibers, while the complete laser spectroscopy system consists of a spectrograph, an integrating sphere and a photodiode array as a detector element. The determination of the optical properties of soft and hard biological tissues -- in vitro -- was performed with both systems. Spectral information obtained, the appropriate mathematical modeling and the comparative results are discussed.

In the present work we report the results of the measurement of the angular distribution of laser light reflected from a rough tooth surface and of Monte Carlo simulation of the 3-D process of photons migration in a two-layered human enamel- dentin structure. The measured reflected patterns are as a whole asymmetric and more spread than the calculated by the simulation. The measured total diffusely reflected power reaches 3 - 20% from the irradiating power. An increase in the total absorbed energy as well as in the spread of absorption is observed below the enamel-dentin interface. The scattering anisotropy affects in a different way the absorption below the tooth surface: the highly forward peaked phase function leads to decrease of absorption just below the air-enamel boundary and rise of absorption below the enamel-dentin boundary.

CO₂ laser-tissue interaction results in the ejection of destruction products from the irradiation zone and the radiation scattering at these products. The autodyne detection of Doppler-shifted backscattered radiation gives the possibility to obtain the information directly from laser- tissue interaction zone. Some possibilities of such Doppler diagnostics are demonstrated.

We review the history and capabilities of UMIST's Rapid- scanning Lidar (RASCAL). This is a backscatter Lidar designed to study aerosol dispersion from industrial plant. The system is fully computer-controlled and is based around a frequency- doubled Nd-YAG laser having a pulse repetition rate of 30 Hz. The signal is measured with a 10-bit, 60 MHz digitizer. Overall, a plume cross-section can be obtained in < 2 s and repeated every approximately 4 s. Such scanning can continue for several hours. Range resolution is typically 5 m with sensitivity down two a few (mu) g m^-3 of aerosol. Over 10 years we have developed software to analyze the returns to estimate plume height, spread and intermittency; wind speed at plume height; and mixing layer depth. The backscatter from combustion plant plumes appears to be well enough conserved to allow point measurements within the plume to be interpreted as concentration/flux ratios, (c/Q) for comparison with dispersion models. This technique has recently been successfully tested using a chemical tracer. A substantial dataset acquired with the system has been used to test the predictions of various regulatory models. We present recent comparisons of modelled and measured c/Q at a small power station: the ensemble values show impressive agreement.

In lidar remote sensing the classical lidar equation is normally used for the retrieval of environmental parameters from the return signal. One of the most important reasons for this is the simplicity of this equation which describes the contribution of single scattering to the return signal only. But it is well known that multiple scattering occurs in lidar sensing of dense clouds and remote cirrus clouds. Therefore a more precise description of lidar returns is needed. We use a general stochastic model for the description of the transport of light through the atmosphere. This model is a 'corpuscular stochastic multiple scattering process including polarization, and random change of type of scatterers (for fixed wavelength)' which is (under mild conditions) equivalent to a corresponding general radiative transfer equation. From this exact multiple scattering lidar equation a hierarchy of lidar equations including the classical lidar equation may be derived by introducing simplifying assumptions step by step. Of course, more information about the scattering behavior of the scattering particles or molecules of the atmosphere is needed for such an exact multiple scattering equation, but the more input is necessary the more output is possible. Indeed, it is possible to obtain simultaneously quite different environmental parameters (e.g. extinction and size distribution) from one multiply scattered return signal. We show examples of simulations of multiply scattered returns of a spaceborne lidar from an atmosphere consisting of a mixture of molecules, cirrus, water clouds, and haze with a height dependent extinction coefficient for each component.

This lecture describes the development of lidar techniques to measure the atmospheric temperature profile. Particular attention is given in the lecture to the technique that uses pure rotational Raman scattering of light by molecular nitrogen and oxygen. At present, this approach to temperature profiling in the atmosphere with lidars has received a new impulse because of recent advances in laser and optoelectronics technologies. The instrumentation aspects that determine the feasibility of one or another lidar technique to measure temperature profiles based on the pure rotational Raman spectrum (PRRS) of N₂ and O₂ molecules are considered. The primary instrumental problem is isolation of extremely weak Raman-lidar returns within the PRRS of N₂ and O₂ against the background from the much stronger line of unshifted scattering. Mie + Rayleigh, that simultaneously contributes to lidar returns. Besides, the daytime sky background is the factor that severely hampers daytime lidar measurements especially in the case with Raman lidars. So it is an important task of Raman-lidar technologists to find proper ways to overcome this difficulty that would made it possible the temperature profiling in the atmosphere to be performed whole day round. The approach to achieving this task by use of a Fabry-Perot interferometer (FPI) is discussed in the lecture.

This paper presents a study of the distribution of aerosol extinction coefficient and its time and spatial variations during the morning breeze transition period. The experiment was carried out near the town of Akhtopol with a groundbased aerosol lidar. The results show an existence of characteristic extinction distribution (aerosol stratification) for each stage. In the beginning of the period, when in the lowest 200 m there is still an off-shore breeze, an aerosol layer with high extinction exists at heights of about 150 - 200 m above the sea surface. As the sunheating gets stronger this layer is gradually destroyed. At the end of the period, when the on- shore breeze is already established, in the lowest 200 m, a layer of low extinction is observed at height of about 200 m above the sea surface. A coincidence has been revealed between the heights of the wind changes and location of layers where the extinction differs from the one of the surrounding air. Besides the change in breeze pattern, the change in the relative humidity also affects the observed time and spatial variations in aerosol extinction.

Results of systematic investigations of the aerosol structure of the planetary boundary layer over a part of Sofia city are presented. The study aims at investigation of formation of aerosol distribution after sunrise using a lidar-kytoon system. Lidar data are interpreted combined with profiles of atmospheric thermodynamic parameters determined by conventional means.

A part of the results obtained during the winter experimental campaign 'LIRADEX'98' are presented. A vertically sounding aerosol lidar and a thermal infrared radiometer were used for joint investigation of 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 during November and December, 1998. The data discussed in the presented paper are obtained on December 2, 1998.

Cloud base profiles measured with laser ceilometer are studied using multifractal approach. The method assesses nonstationarity and intermittency pertinent to such highly fluctuating signals. The irregular structure of the signals is a benchmark for non-linear dynamics processes. The analysis searches for the scaling properties of q-th order singular measures and q-th order structure functions. Therefore, the method seeks for various scales of self-affinity, i.e. searches for multi-affinity. We found that multifractality is the signature of the cloud base height profiles, characterized with a hierarchy of exponents q H(q) and K(q). The value of the roughness parameter H₁ is consistent with the one obtained for the same data using different method of analysis. The multifractal behavior is consistent also with the multi- affine properties of other atmospheric data recorded simultaneously during the same field experiment ASTEX'92.

The performance is considered of some coherent-lidar inverse techniques for retrieving high-resolution Doppler-velocity profiles, with a resolution cell that is far below the pulse length and even of the order of the sampling interval. The speckle noise influence on the retrieved Doppler velocity profiles is investigated as a function of the lidar pulse length, the data sampling interval, the ratio between them, and as a whole, of the lidar radiation wavelength. It is shown that at a constant Doppler-velocity sensitivity the speckle noise error increases with the increase of the pulse length and the decrease of the sampling interval. Moreover, a similarity relation is established consisting in that the level of the error is practically invariable when the ratio of the pulse length to the sampling interval is retained. The results obtained lead to the conclusion that shorter- wavelength lidar radiation should be used not only to retain a good Doppler-velocity sensitivity at shorter pulse lengths, but to retain as well a satisfactorily high accuracy of retrieving the Doppler-velocity profiles, with proportionally shorter range resolution cell.

The lidar technique used provides simultaneous recording of parallel and cross polarized components of the returned signal at different viewing angles of the receiving optics. The experimental data consist of time series of both polarized components recorded from different distances along the sounding path within the cloud. The auto-correlation functions of both polarization components are calculated using the time series of the lidar signal obtained at different distances. The auto-correlation functions of the parallel component of the lidar signal show two zones within the cloud, where the aerosol backscattering coefficient has close values. The auto- correlation functions of the cross component of the signal reveals the existence of a similar zone, which determines the area which the multiple scattering develops in the same manner. The cross-correlation functions of the parallel and cross components of the polarized signals confirm our suggestions as they show a time delay of approximately 150 ns.

Investigation of new aspects of application of pulsed quantum well (In)GaAs/AlGaAs diode lasers to atmospheric spectroscopy and lidar remote sensing is reported. The presented method utilizing these powerful multichipstack diode lasers of broad radiation line is approved theoretically and experimentally for monitoring of atmospheric humidity. Molecular absorption of gas species in the investigated spectral band 0.85 - 0.9 micrometer implemented by laser technology initiates further development of prospective DIAL analysis. A mobile lidar system is realized, employing optimal photodetection based on computer-operated boxcar and adaptive digital filter processing of the lidar signal in the analytical system. Aerosol profile exhibiting cloud strata in open atmosphere by testing of the sensor is demonstrative of the efficiency and high sensitivity of long-range sounding.

Recent experiments conducted using a ground-based lidar have shown that laser-induced fluorescence spectral emissions from green plants are detectable from a remote platform. A pulsed Nd-YAG laser emitting at 532 nm was used as an excitation source. The fluorescence maxima in Populus tree were found to be at 685 nm and 740 nm. An increase of the ratio 685/740 nm between the intensity maxima of the fluorescence spectra was observed for that tree in the case of water stress. The morphological differences or difference in the photosynthetic properties between the two sides of the leaves cause differences between the ratios of the intensity maxima at 685 nm and 740 nm of the fluorescence spectra observed in cases of different geometries of measurement during the laboratory study.

The image quality of the laser sounding of distant objects is limited mainly by the resolution of the optical system 'a telescopic objective -- a turbulent layer.' Fried formulated a theoretical expression concerning the system's resolution, but he assumed a diffraction-limited objective. Our goal here is to increase the estimation accuracy of the resolution of lidar optical systems, using the measured in advance resolution of the receiving objective. We show the possibility to substitute the maximum angular frequency of a diffraction- limited objective, in the expression of the optical transfer function, by the measured angular frequency of the actual objective. We propose a method, based on measuring the common resolution of the system 'a lidar telescope -- a turbulent layer,' for estimating the structural constant Cn2 of the turbulence. We have also calculated numerically the resolution of such a system for one-kilometer turbulent layer.