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Spectral and kinetic characteristics of photoluminescence of commercial YAG:Ce phosphors excited both by laser radiation in the range of 4–6.415 eV and by beams of electrons with energy of 250 keV are investigated. It is shown that electron-hole (e-p) pairs are formed in the matrix by electron beam and upon exposure to laser radiation at 193.3 nm (6.415 eV) as well. All excitation methods initiate the band in the range of 560 nm caused by Ce3+ ions and the UV bands at 320 nm and 360–380 nm. UV luminescence is due to luminescence of intrinsic lattice defects. Possible processes of energy transfer to luminescence centers under optical excitation in the range of 4–6.415 eV are discussed.

The paper presents results of experimental study of the dynamics of laser-induced fragmentation of nitrobenzene molecules. It has been shown that when two laser pulses interacting with nitrocompound molecules and their decay products (NO fragments) are time delayed, it is possible to increase the sensitivity of the method of laser fragmentation/laser-induced fluorescence by approximately an order of magnitude for an optimal time delay between the pulses.

Results of investigations into the development of effective N2-lasers pumped by a longitudinal discharge with specific pump powers exceeding 3 MW/cm3 are presented. It is shown that the main reason that limits the duration and energy of the output beam is unstable burning of the diffusion discharge in these modes of laser operation. Methods of forming the diffusion discharge are proposed that allow the lasing pulse duration to be increased from 5 to 20 ns.

We report the results of investigations aimed at raising the peak output power of a THL-100 visible-range hybrid femtosecond laser system based on a XeF(C − A) photodissociation amplifier. The increase in power was achieved due to the shortening of the pulse duration at the system output by broadening the spectral profile of the second harmonic from 5.3 to 8 nm, which takes place in the transformation of a negatively chirped pulse of the fundamental frequency radiation in a nonlinear KDP crystal. After the KDP the radiation pulse was stretched to 1.8 ps in a prism stretcher and amplified in the XeF(C − A) amplifier. The energy obtained at the amplifier output was 1.2 J. After compression of the amplified output pulse, its duration was equal to 29.4 fs, which means that a peak output power of 40 TW was reached at the output of the laser system.

The results are presented from experimental studies of the emission of NO radicals in a filament of femtosecond radiation produced in a N2/NO2 gas medium with total pressures of up to 1 atm. It is shown that in the recorded emission spectrum of the filament, emission transitions A2Σ+ (ν' = 0–2) – X2Π (ν'' = 0–5) of NO molecules are observed at concentrations of NO2 gas of up to 10 ppb−1. It is shown that the intensity of emission of NO A–X molecules grows along with the nitrogen pressure, due to the intermolecular nonradiative transfer of energy from the metastable $${{{\text{A}}}^{{\text{3}}}}\Sigma _{u}^{ + }$$ level of a N2 molecule to the electron A2Σ+ level of a NO molecule.

The results of remote detection of objects containing explosives with a lidar detector of traces of explosives in combination with a portable express gas chromatograph are presented. It is shown that the lidar detector of traces of explosives confidently detects the simulators of TNT, hexogen, and PETN from a distance of 5 m when sounding the surface of a sample. Laser action on the sample surface causes desorption of vapors, which are reliably detected by the gas chromatograph. It is shown that the joint use of the laser sounding and gas chromatography techniques makes it possible to increase the reliability of detection of explosives. The prospects of using the gas chromatography in the development of laser sounding techniques are determined.

In this work, we study the process of laser photolysis of NO2 molecules followed by fluorescence of NO radicals when interacting with broadband radiation from an ArF laser. It was shown that in the presence of nitrogen dioxide in the cuvette with a pressure of 1 mbar, the spectral distribution of fluorescence includes high-intensity spectral bands that correspond to optical transitions NO C2Π (v' = 0) → NO X2Π (v'' = 0-4). When helium with the ratio He / NO2 = 1000/1 mbar was added to the cuvette, intense fluorescence was observed at optical transitions from the electron-vibrational levels of NO C2Π (v' = 0) and A2∑+ (v' = 3) to the ground state X2Π (v'').

Results of numerical and experimental studies of the control of optical elements of a KrF laser cavity by use of the image processing method are presented. Different methods of beam image binarization for determining the boundary dimensions and flattening the distribution of its radiation intensity are considered. Conditions allowing one to accelerate the process of dispersive cavity adjustment in the automatic regime of laser operation and to restore the initial parameters of the output beam with an accuracy of up to 5% are determined.

The results of studying the 2D-simulation of evolution of a diffusion channel in the KrF-laser pump discharge initiated by the pin on the cathode surface are presented. It is shown that during the pump pulse, the inhomogeneity passes successively through three stages: a plasma spot on the cathode surface, a diffuse channel, and a high-conductivity channel. From the analysis of the dynamics of spatial distribution of spontaneous emission on the B0-X transition of the KrF molecule in such a discharge, it is obtained that the channel can work as an amplifying medium while the volumetric form of its glow is maintained. Despite the contraction of the channel into a narrow cord at the end of the pump pulse, the distribution of the radiation energy over the entire pulse has the shape of a torch with the width at the anode of ~0.6 cm.

Results of investigation of the parameters of the THL-100 hybrid laser system of visible range developed at the IHCE SB RAS in collaboration with the LPI RAS are presented. The laser system consists of the Ti:Sa Start-480M starting complex and the photodissociation XeF(C-A) amplifier with aperture of 24 cm. The starting complex provides 50-fs spectrally limited radiation pulses with energy of the second harmonic (475 nm) up to 20 mJ and 50-ps positively chirped radiation pulses with energy up to 5 mJ. The active medium of the XeF(CA) amplifier is created in the XeF2/N2 mixture upon exposure to VUV radiation of xenon excited by a highpower electron beam. It is demonstrated that record power of 14 TW is attained by amplification of negatively chirped radiation pulse with duration of 1.6 ps in the XeF(C-A) amplifier, and maximum energy of ~3.2 J is realized by amplification of positively chirped radiation pulse.

The results of studies on the development of laser sources in the UV and IR spectral ranges for the lidar systems operating on the basis of a method of laser fragmentation with subsequent laser-induced fluorescence (LF/LIF) are presented. It is shown that LF/LIF is an effective method for the remote detection of harmful and dangerous substances including nitrogen oxides in the atmosphere. The formation of a high-quality sounding UV radiation in excimer lasers and its transportation along the atmospheric path is studied. The causes are revealed that lead to the formation of noise arising in the atmosphere and limiting the sensitivity of the applied method.

The optimization of geometrical parameters and calculation of the force fields of trans -acrolein (CH 2 CHCHO) in the ground S 0 and lowest excited triplet (T 1 ) and singlet (S 1 ) electronic states are performed at the CASPT2/def2-TZVPP theoretical level. Co-assignments of the vibrational frequencies calculated from the corresponding force fields are validated by calculations of the analogs of the Duschinsky matrix for the pairs of the (S 0 , T 1 ) and (S 0 , S 1 ) electronic states. The results obtained by comparing the vibrational frequencies calculated from the scaled force fields with the experimental vibrational frequencies made it possible to corroborate some details of the molecular structure in these electronic states.

The results of experimental investigations of the discharge plasma emission spectrum in high-pressure gases, including fluorides, are presented. For the gas mixtures Ne/Kr/F 2 and Ar/Kr/F 2 , the emission transitions of KrF * and Kr 2 F * excited molecules emitting in the ultraviolet and visible spectral range are experimentally studied. It is established that growth of Kr content from 10 to 400 mbar in the gas mixture leads to an increase in the fluorescence intensity of Kr 2 F * molecules. The stable bulk discharge in a few oscillation periods of the current pulse pump in excimer gas mixtures is demonstrated. It is shown that the bulk discharge in Ar/Kr/F 2 =1000/400/1 mbar mixture forms the active medium on the Kr 2 F * molecules with a gain of 3.14×10 −4 cm −1 .

The first experimental results obtained in visible range using the THL-100 multi-terawatt hybrid laser system after modernization of the starting femtosecond complex and the gas amplifier are reported. The modernization was performed to increase the output beam power at the expense of changing the configuration of the vacuum diode of the electron accelerator used for pumping of the XeF(C-A) amplifier. As a result, the increase of the VUV radiation pumping energy of the active medium of the XeF(C-A) amplifier by 30% is attained. This leads to doubling of the output laser beam energy of the XeF(C-A) amplifier.

The results of experimental studies aimed at increasing the power of THL-100 hybrid laser system are presented. The laser system consists of Ti:Sa front-end, operating at the central wavelength of 950 nm, second harmonic generator (SHG), prism stretcher, gas XeF(C-A) amplifier, and compressor based on fused quartz plates. In these experiments the SH spectrum broadening in a nonlinear crystal was realized, which allows to reduce its pulse duration from 50 to 30 fs. This radiation pulse was extended in the prism stretcher to 1.8 ps and amplified in the XeF(C-A) amplifier. At the output of amplifier 1.2 J energy was obtained. After compression, this laser pulse had duration of 29.4 fs and peak power of 40 TW. It is the second highest peak power value in visible spectrum range.

The results of experimental and numerical studies of the possibility of formation of an active medium on a Kr 2 F trimers in the discharge plasma, are presented. It is demonstrated that the trimer fluorescence includes three spectral bands corresponding to wavelengths of 414, 456 and 503 nm. It is shown that the experimentally measured gain of the active medium on the Kr 2 F trimers is g = 3.14×10-4 cm-1.

The latest results obtained in THL-100 hybrid femtosecond laser system operating in the visible spectral range are presented and the ways of the peak power increase of the laser beam are discussed.

The possibility of remote detection of traces of explosives using laser fragmentation/laser-induced fluorescence (LF/LIF) is studied. Experimental data on the remote visualization of traces of trinitrotoluene (TNT), hexogen (RDX), trotyl-hexogen (Comp B), octogen (HMX), and tetryl with a scanning lidar detector of traces of nitrogen-containing explosives at a distance of 5 m are presented.

Results from studying the conditions under which spectra generated by a 50 fs pulse from a Ti:Sa setup broaden at a wavelength of 475 nm are described, along with how to compensate for the accompanying positive dispersion. It is shown that the width of the spectra grows from 5 to 15 nm when the thickness of K8 glass is optimal. Pulse recompression with a spectral width of a 12.2 nm is achieved, along with a pulse duration of 22.6 fs.

Results of experimental studies of the chemical HF laser with a non-chain reaction are presented. The possibility of the total laser efficiency of 5 % is shown when a traditional C-to-C pumping circuit with the charging voltage of 20-24 kV is used. It is experimentally shown that the specific radiation output energy of 21 J/l is reached at the specific pump energy of 350 J/l in SF6/H2 = 14/1 mixture at the total pressure of 0.27 bar.

The results of the formation and amplification of positive chirped 0.1 ns laser pulse at a central wavelength of 470 nm in the laser system THL-100 are presented. It is shown that a front-end allows forming a radiation pulse with a Gaussian intensity profile and the energy up to 7 mJ. At amplification in XeF(C-A) amplifier of the pulse with 2-5 mJ energy a saturated mode is realized and 3.2 J output laser beam energy is reached.

The KrF laser with radiation pulse duration at half maximum of 20 ns is experimentally investigated. A selfconsistent model is developed considering the electric circuit, the kinetic processes in the active medium, and the formation of laser radiation in a resonator. Time dependences of the discharge current and voltage on the capacitor and discharge electrodes, plasma particle concentration, and rate constants of the processes determining the characteristics of the discharge and laser radiation are presented. Processes are revealed that determines the characteristics of the space charge and laser radiation. The kinetics of the processes of production and annihilation of KrF excimer molecules is studied in detail. It is demonstrated that high rates of destruction of excimer molecules increases the time of delay of generation thereby decreasing the efficiency of laser generation and limiting the possibility of decreasing laser radiation pulse duration.

Results of 2D simulation of a KrF laser are presented. In the model, inhomogeneities of distributions of the electric field and plasma particle concentration are considered. It is demonstrated that starting from electron concentration of ~1014 cm–3, the rate of electron production depends on the electron concentration ne. This changes the distribution of the concentration ne over the discharge width. If we estimate the discharge width from the electron concentration at half maximum, than depending on the pumping mode, the discharge width decreases by an order of magnitude by the end of the lasing pulse. In addition, it is demonstrated that the laser beam width is larger than the width of the electron concentration profile at half maximum.

The influence of the composition of a gas mixture in a XeF(C-A) amplifier of the THL-100 hybrid femtosecond laser system on the main channels of energy loss is studied via numerical simulation. It is shown that an increase in the N2 buffer gas pressure from 100 to 760 Torr increases the fraction of absorbed energy transferred to the upper laser level XeF(C,ν = 0), while an increase in the XeF2 partial pressure increases energy loss in collision quenching of the XeF(B, C) states and reduces the energy transferred to the XeF(C,ν = 0) state.

TEA CO2-lasers generating short pulse radiation and operating in a pulse-periodic mode with the repetition rate up to 10 Hz have been developed. It is shown that the addition of nitrogen up to 8% in the mixture of molecular gases СО2:H2 = 500:50 at a total pressure of P = 0.6 bar enhances the peak emission power maintaining the temporary pulse shape. An output beam intensity of 12.3 MW/cm2 was obtained for the 30 ns pulse at a laser efficiency of 2.8%. In a compact TEA СО2-laser with an active medium volume of 6 cm3, a beam with an output intensity of 24 MW/cm2 at pulse duration of 70 ns was obtained.

Results of experimental and theoretical investigations of the hybrid (solid state/gas) visible-range femtosecond systems THL-100 (IHCE SB RAS) and THL-30 (P.N. Lebedev Physics Institute) based on a Ti : sapphire front end and a photochemical XeF(C–A) amplifier are reported. The front end generates 50-fs optical pulses with the second-harmonic (475 nm) energy of up to 5 mJ. The active medium of the amplifier is produced in a mixture XeF2 – N2 subjected to VUV radiation of xenon excited by an electron beam. The computer model is developed for calculating parameters of the XeF(C – A) amplifier, which is in a good agreement with experiments. In the THL-100 system with the 25-cm output aperture of the XeF(C–A) amplifier, a record visible-range femtosecond radiation peak power of 14 GW was obtained in a 50-fs pulse with the time contrast of above 108. The measured power of an amplified spontaneous emission of the XeF(C–A) amplifier in the angle of 0.2 mrad was 32 W. The result obtained testifies that the hybrid approach to the development of ultrahigh-power systems provides a high time contrast of radiation (greater than 1012 for the projected peak power of 100 TW). In the THL-30 system, prospects for shortening an amplified femtosecond pulse are studied and it is experimentally shown that by compensating a third-order dispersion in a hybrid system one can obtain pulses with duration of at least 27 fs with a recompression of amplified pulses in bulk glass. Also, a new phenomenon was observed of spectrum broadening and self-compression of negatively chirped femtosecond pulses in the visible range under a nonlinear interaction of wide-aperture beams with fused silica. This result opens prospects for development of the new methods of selfcompression for femtosecond pulses that are lacking physical limitations on pulse energy and realisation of self-compression of amplified pulses in the output window of the XeF(C–A) amplifier.

Stable glow of the discharge of various types in the gas mixture of a XeCl laser is investigated for specific pumping power in the range 1.2–4.6 MW/cm3 and pulse duration of 40 ns. It is demonstrated that formation of partially homogeneous plasma with many intensive cathode spots on the electrode allows the maximum energy and duration of the lasing pulse to be obtained with laser efficiency of 2.4%. It is revealed that for the specific pumping powers up to 1.5 MW/cm3, a very homogeneous volume discharge with a small number of lowintensive cathode spots is formed in the discharge gap. With further increase in the specific pumping power exceeding 4.5 MW/cm3, current microinhomogeneities are formed in the volume discharge of this type leading to lasing breakdown.

THL-100 hybrid femtosecond laser system operating in the visible spectral range and the experimental results obtained by now are presented.

This paper reports on the creation of a THL-100 multi-terawatt hybrid laser system based on a Start-480M titanium-sapphire starting complex and photochemical XeF(C-A) amplifier with a 25-cm aperture. The complex produces 50-fsradiation pulses of energy up to 5 mJ at a second harmonic wavelength of 475 nm. The active medium of the amplifieris created in a XeF 2 /N 2 mixture under vacuum-ultraviolet radiation of electron beam-excited xenon. The results of firstexperiments on femtosecond pulse amplification in the active medium of the XeF(C-A) amplifier are presented todemonstrate that a laser beam peak power of 14 TW has been attained.Keywords: Chirped pulses; Femtosecond pulses; Hybrid (solid/gas) laser system; Photochemical XeF(C-A) amplifier;Second harmonic INTRODUCTIONAt present, the development of ultra-high power laser sys-tems with a pulse duration of 10–100 fs is based mainly onnear-infrared solid-state titanium-sapphire or parametric am-plifiers and amplification of positively chirped pluses, i.e.,stretched in time (0.5–1 ns), by linear frequency modulation(Strickland & Mourou, 1985) with their subsequent com-pression to the initial duration. Stretching of a pulse is re-quired to decrease its power below a threshold at which thebeam is self-focused; in solid-state systems, pulses are nor-mally stretched about 10

A unique ultraviolet laser system has been developed for a lidar intended to detect nitrogen oxide molecules in the atmosphere. The electric-discharge KrF laser system is capable of producing a highly coherent laser beam with practically the same energy over a spectral range of 247.5–249.5 nm. At the edge of the amplification band in the range 247.5–247.8 nm, the system produces a beam of energy 0.3 J, pulse duration 16 ns, and spectral line width 2 pm. Atmospheric sounding by using this beam with an energy density of 200 mJ/cm2 in the scattered signal has detected noise in the 226 and 236 nm bands whose intensity increases the laser beam pulse repetition rate and energy density.

Scaled quantum mechanical force field (SQM-FF) vibrational analyses of the gauche,Trans,trans,Trans,gauche-conformers of octa-1,3,5,7-tetraene (I) with C i and C 2 symmetry at the HF/6-31G//HF/6-31G computational level were used to identify the rotational isomer observed in the IR spectrum of this excited molecule in the solid state. Geometry optimizations at the MP2(FC)/aug-cc-pVDZ level show that the two non-planar structures of gTtTg-I have the terminal -CH=CH2 moieties rotated by ∼30.6° with respect to the remainder of the nearly planar skeleton. The MP2 and HF energies of the C 2 conformer are slightly lower than the corresponding values of the C i conformer. A set of the experimental wavenumbers relating to the C 2 conformer was determined by the detailed analyses of the experimental IR spectra of compounds obtained by Datta et al. via photolysis of 1,3,5-cycloterraene and bicycle[4.2,0]octa-2.4-diene. The available experimental wavenumbers correlate better with the results of our SQM-FF calculations at the HF/6-31G level for the conformer with C 2 symmetry than for the conformer with C i symmetry. In further support of these results, the van der Waals molecular volume of the C 2 conformer was calculated to be somewhat smaller than the volume of the C i conformer, suggesting that in the solid state, where the close-packing principle comes into play, the C 2 conformer would be preferred.

The parameters of electric-discharge pulse-periodic XeCl lasers with a pulse duration of 25 - 40 ns, an energy of 0.2 - 0.7 J, and a pulse repetition rate up to 100 Hz have been investigated. It is shown that the total laser efficiency of 2.6 % and the maximum efficiency with respect to the stored energy of 3.8 % are obtained at a specific pump power of 2.8 - 3.3 MW cm-3 and a discharge circuit inductance of 3.5 - 4 nH.

An assignment of the out-of-plane vibrations of the trans-buta-1,3-diene molecule was performed by analysis of the isotopic shifts of wavenumbers in the methylene moieties =CHX, where X = H, D or T. A suggestion for the mutual reassignment of the wavenumbers belonging to the twisting vibration of the methylene moiety =CH2 and the out-of-plane vibration of the methine moiety =CH— was shown to be incorrect.

Due to the publication of a number of contradictory assignments of the vibrational wave numbers of rotational isomers of Acrolein in the ground electronic state, the analysis of their vibrational spectra is repeated based on the previously calculated scaled ab initio force fields. With the use of the reported results that predicted the force fields of trans-acrolein in the 1(n,π*) and 3(n, π*) states at the CASSCF/cc-pVTZ level, the experimental vibrational bands are analyzed in these excited electronic states based on well-established regularities. It is noted that in the assignment of the calculated vibrational wave numbers of the molecule, the isotopic shifts in the ground and excited electronic states 1(n, π*) and 3(n, π*) are taken into account. The previously considered calculated potential curves of the internal rotation of acrolein in combination with the data on the difference in the enthalpies (ΔH0) of conformers allow a choice to be made in favor of one of the variants of the torsional vibration wave numbers that have been reported in the literature.

The parameters of ultrasonic testing equipment and techniques of producing 2D ultrasonic images of welds at frequencies of 10–50 MHz are given.

The generation of nanosecond and subnanosecond pulses in a XeCl laser is studied. The short radiation pulses are generated in a resonator with a SBS mirror. By focusing laser radiation inside and on the surface of a nonlinear medium, it is possible to generate pulses of duration 3 ns and 150 ps, respectively. The laser beams obtained in this way contain more than 70% of energy within the diffraction angle and have the signal-to-noise ration exceeding 104.

The wave numbers of trans-2,3-13C2-buta-1,3-diene were calculated using a scaled quantum-chemical force field found at the MP2/6-31G*//MP2/6-31G* level of theory. The obtained results and the theoretical sets of wave numbers for twelve deutero and 13C derivatives of the trans form and five deutero and 13C derivatives of the gauche form of buta-1,3-diene found previously at the MP2/6-31G*//MP2/6-31G* level are compared with the corresponding experimental vibrational spectra corrected for the Fermi resonance. Combined analysis of the vibrational spectra of the above mentioned isotopomers was performed.

The geometrical parameters and quantum mechanical force fields (QMFF's) of 3,3-dimethyl-1-(trimethylplumbyl)cyclopropene (I), 3,3-dimethyl-1-(t-butyl)cyclopropene (II), 3,3-dimethyl-1-(trimethylsilyl)cyclopropene (III), 3,3-dimethyl-1-(trimethylgermyl)cyclopropene (IV), and 3,3-dimethyl-1-(trimethylstannyl)cyclopropene (V) were calculated at the pseudopotential (HF/SDDAll) level. Analysis of the optimised geometrical parameters was performed. The set of scale factors for correction of the pseudopotential QMFF of III was determined using its earlier well-characterised vibrational spectrum. Transferral of the set of scale factors obtained for III to the QMFF's of I, II, IV and V was followed by calculation of the fundamental vibrational frequencies. Analysis of the results for these molecules revealed some peculiarities in the vibrational frequencies obtained at the pseudopotential level.

The results of experimental research on an x-ray source intended for preionizing the laser mixture in wide-aperture electric-discharge excimer lasers are presented. An experimental prototype of the source in which an x-ray radiation pulse is formed in an inverted-type vacuum diode during braking of accelerated electrons in a tantalum foil has been developed. It is shown that the use of a metal-dielectric cathode allows generation of x rays with nonuniformity of the intensity distribution within limits of 10% at an energy of quanta no higher than 55 keV and a radiation exposure dose 160 mR.

Results of experimental measurements and numerical simulations of the N 2 and XeF 2 gas pressure effects on the gain characteristics are presented in the paper. It is experimentally and theoretically is shown that maximum total gain (5-6)×10 4 achieved at a pump energy E = 240 J, 0.2 Torr XeF 2 and 0.5 atm N 2 pressure. Increasing and decreasing of N 2 pressure leads to decrease of the gain. The possibility of the XeF(C-A) amplifier operation in a generator mode is discussed and the theoretical study results of generation are presented. It is shown that an annular laser radiation with energy up to 8.5 J can be obtained. The study results of the influence on the laser energy of N 2 and XeF 2 pressure and reflectance coefficient of output mirror are presented.

The possibility of remote detection of traces of high energetic materials using laser fragmentation/laser-induced fluorescence (LF/LIF) method is studied. Experimental data on the remote visualization of traces of trinitrotoluene, hexogen, composition B, octogen, and tetryl obtained at a distance of 5 m with a scanning lidar detector of traces of high energetic materials are presented.

Detailed model study of THz generation by CO 2 laser down-conversion in pure and solid solution crystals GaSe 1-x S x is carried out for the first time. Both forward and backward co llinear interactions of common (eo-e, oe-e, oe-o, oo-e, ee-o) and original (ee-e, oo-o) types are consid ered. Possibility of realization, phase ma tching angles and figure of merits are estimated for line mixing within 9 P m and 10 P m emission bands, as well between them. Dispersion properties of o- and e-wave refractive indices and absorption coefficients for GaSe, GaS and GaSe 1-x S x crystals were preliminary measured by THz-TDS, approximated in the equation form and then used in the study. Estimated results are presented in the form of 3-D figures that are suitable for rapid analyses of DFG parameters. The most efficient type of interaction is eo-o type. Optimally doped (x = 0.09-0.13) GaSe 1-x S x crystals are from 4 to 5 times more efficient at limit pump intensity than not doped GaSe crystals. Keywords: GaSe, GaSe

The quantum mechanical force fields (QMFF's) of 3,3-dimethyl-1-(tert-butyl)cyclopropene (I), 3,3-dimethyl-1-(trimethylsilyl)cyclopropene (II), 3,3-dimethyl-1-(trimethylgermyl)cyclopropene (III), and 3,3-dimethyl-1-(trimethylstannyl)cyclopropene (IV) were calculated at the HF/3-21G*//HF/3-21G* level. The set of scale factors for the correction of HF/3-21G*//HF/3-21G* QMFF of II was determined using its well-characterised vibrational spectrum. Transferral of the set of scale factors obtained for II to the QMFF's of I, III and IV and calculation of the fundamental frequencies resulted in good agreement between the calculated and previously assigned experimental frequencies of III. This again demonstrates the feasibility of transferral of a set of scale factors obtained for the correction of the QMFF of a molecule to others containing heteroatoms from the same column of the Mendeleyev Periodic Table. Thus the calculations performed permitted the accurate assignment of the fundamental vibrational frequencies in the experimental IR spectrum of IV. The vibrational frequencies of 3,3-dimethyl-1-(tert-butyl)cyclopropene (I) were also calculated from the HF/6-31G*//HF/6-31G* QMFF, scaled by the set of scale factors used previously for the HF/6-31G*//HF/6-31G* QMFF's of II and III. Regularities in the trends of some vibrational frequencies with increasing atomic number of the heteroatom are observed.

Quantum mechanical geometry optimizations and the calculation of vibrational frequencies of hexafluoroethane have been performed at the HF/6-31G*, MP2/6-31G*, CCSD/cc-pVDZ, and B3LYP/6-31G* levels. The force fields obtained were scaled. The necessity is stressed of carrying out the detailed analysis of the vibrational spectra of small reference molecules to determine sets of scale factors which are transferable to quantum mechanical force fields of large molecules for the purpose of predicting their vibrational spectra.

An excimer laser system having an output aperture diameter of 40 cm and consisting of five lasers, three of which are excited by an electric discharge and the remaining two by an electron beam, is built. The first laser produces a 308-nm radiation with a duration of 200—250 ns, a spectral linewidth of 0.9 cm-1 and the beam divergence close to the diffraction limit. This pulse is amplified in the active media of the other lasers. As a result, radiation with an energy of 5 J, spectral linewidth 0.9 cm-1 and beam divergence 37 μrad is produced at the output of the third laser. The output energy of the entire system amounts to 330 J and the pulse duration is 200—250 ns.

Two-high power excimer laser systems with square (25 × 25 cm) and circular (with a diameter of 40 cm) cross sections of the output laser beam are described. The first (second) system consists of four (five) excimer lasers. The experimental results on the generation of the high-quality high-power laser pulses are presented. Laser beams with a pulse duration of 1–250 ns, a divergence of 0.01 mrad, a spectral line width of 0.01 cm−1, and a pulse energy of up to 330 J are obtained.