With the help of the self-consistent ABCD matrix method the fundamental normal mode of a four-mirror cavity with active rod and hard aperture is analyzed. Cavity parameters ranges with the small diffraction losses at hard aperture and the decreased diffraction losses for the increased mode intensities due to self-focusing in active medium are shown immediately for practical Kerr-lens mode-locked Ti:sapphire lasers. The fluctuation model of self-mode-locked lasers is used to demonstrate the generation of a stable ultra-short pulse train by the system under constant pumping for the obtained cavity parameters.

The generation dynamics of a linear He-Ne laser at (lambda) equals 1.15 micrometers with rotation and simultaneous harmonic oscillations of resonator anisotropy directions is investigated theoretically. It has been found that modes with a polarization ellipse rotation with frequency greater than the rotation frequency of modulator anisotropy directions may be possible both in a resonator and in a laser. The two-parameter diagram constructed indicates the regions of `positive' rotation and of torus-attractors with resonant two-period cycles.

Pump modulation is used to explore multimode interactions in an standing-wave Nd:YAG laser. Large amplitude modulation drives the system into apparent period doubling cascades and chaos as are expected for the nonlinear oscillations of the driven relaxation oscillations of the laser. However, examination of the intensity fluctuations and intensity power spectra of individual modes indicates that anti-phased fluctuations and subharmonic resonances are quite common and that they masquerade as simpler period-doubling phenomena. Even the sinusoidal response of a multimode laser to weak modulation is found to reveal multimode couplings in the distortions of the resonant frequency and width of the resonance as the pump current is raised, bringing more modes into the dynamics and strengthening the side modes.

The abilities of TEA-CO₂ laser controlling by LC modulators have been investigated. It is shown, that beam direction, beam profile, energy and time position of the pulse can be controlled by LC modulators. Some problems of interaction of radiation with LC are discussed.

At present, to solve a number of technological problems and to conduct various researches, electhcdischarge C°2 ' operaling in continuous and repetitively-pulsed (RP) modes with powers of up to 10 kW are used. The demand for 10-1000 kW lasers sets a problem of stable high-energy deposition into an active medium of rat1r large (hundreds ofliters) volume. Co2laserswith diffusion cooling usually employ a self- sustained discharge in tubes. In such a scheme, maximum power depends on the tube length only rather than on radius and constitutes 100 W/m. A number of setups - "Kometa", "Kardamon", are based on this principle, the top power of which won't exceed several kW. In TRINFI an MKTL-1O laser with the output power of 14 has been developed. The drawbacks of this type of lasers are short service life, difficulties in operation because of the oil cooling of the tubes as well as fragility of the structure. That's why high power lasers use airfuel mixture convective cooling by a gas flowing through a discharge area 2• Amongthe lasers ofthis type we can mention: LT1-2 (TRIMTI), Slavyanka (NIIEFA), LT-S (Shatura). They feature a triple mixture circulation through the entire loop, aclive-medium low pressure (30-60 Torr) and resonator alignment with the discharge area. The parameters of the most widely used LT1-2 lasers are shown in Table 1 . i.asers with a closed loop have a decrease in output power because of changes in mixture composition due to chemical pmcesses. The solution to this problem resides in partial renovation of the working gas mixture (03-1%) or in addition of stabilizing substances to the laser mxture. The best experimental results were obtained with the additive: 1.7%CO+1.4%H Fig.1 shows that the extent of CO2 dissociation with such an addition is only 20% within 4 hours of operation1.

The results of an experimental study of the laser action on XeCl^*, KrF^*, and N₂ molecules and by the atomic transitions of xenon and neon are presented. Laser radiation energies of 110, 90, 3, 100, 50, and 0.5 J have been obtained at (lambda) equals 308, 249, 358, 1730, 2030, and 585 nm, respectively. The experiments were carried out on two accelerators producing radially convergent electron beams, that pumped laser chambers 20 mm in diameter with a beam current of FWHM duration 0.3, 30, and 100 microsecond(s) .

Advantages of coaxial radio-frequency excited discharges for the design of slow-flow and fast- flow high power CO₂ lasers are discussed. The crucial point of the development of such laser systems is the feasibility of resonators with high extraction efficiency and high focusability. Azimuthally unstable resonators prove to be suitable for these annular gain media. A theoretical description of such resonators is compared with experimental results with both slow-flow and fast-flow discharges.

A high-power KrF laser system based on a wide-aperture electron-beam pumped excimer laser `GARPUN' with injection-locking from a discharge pumped narrow-band oscillator has been developed. The laser radiation spectral brightness of approximately 5 X 10¹⁴ W/cm² srad cm^-1 with narrow linewidth approximately 0.1 cm^-1 tunable near (lambda) equals 248 nm, and the output peak power of approximately 1 GW have been obtained.

A current status and perspectives of the work on a high density polarized ³He target are reported. The problems of high-power laser design for optical pumping are discussed. A general formulation for the analysis of an arbitrary linear resonator with internal lens of variable focal length, which represents the rod of a solid-state laser is presented. It is shown that mode spot size is stable with respect to lens optical power fluctuations in one part of resonator when it reaches a minimum on a laser rod. The rules for the design of stable resonators with two or more variable lenses are proposed.

The output characteristics of the continuously operated femtosecond Ti-sapphire laser are given. The dependence of generated beam parameters on mismatching focusing arm length of cavity has been experimentally investigated. The modulation processes affecting on the pulse regime start are discussed.

The nonlinear non-radiative interaction processes lead both to up-conversion of excitation and population of the upper-lying levels, and to the luminescence quenching nonlinear with respect to the excitation intensity. As is evident in this case, a change in the decay kinetics of the given term should be observed. Besides, the probabilities of nonlinear non-radiative interaction depend on the concentration of excited ions. In this work we considered the prospects of development of the visible and IR laser-diode pumped lasers based on TR³⁺-doped double-fluoride crystals. The luminescence spectra of Er ions in LiYF₄ (YLF) crystals were recorded at the up-conversion pumping at different temperatures, the mechanisms of the inverse population of the laser levels produced with selective IR pumping are discussed.

The construction of 1 TW Nd:glass laser system with pulse compression is described. The laser system consists of master oscillator with self-mode locking and negative feed-back, stretcher, regenerative amplifier, two preamplifiers, amplifier chain and diffraction gratings compressor. The possibilities of improving the laser system parameters are discussed.

Evaluations of the average power limits of YAG:Tm-Ho and YAG:Yb-Ho slab-lasers, transversely pumped by the radiation of the laser diode array, are carried out on the base of the detailed study of the energy conversion processes in the active media.

It's noted that in spite of a wide variety of record results reached up till now for experimental models of Titanium-Sapphire (Ti-Sa) lasers, there is a great market demand for commercial models of nanosecond pulsed lasers, as well as of ultrafast modelocked CW lasers. The commercial models of research-quality nanosecond tunable Ti-Sa lasers developed and manufactured by SOLAR are considered.

The paper reviews recent results obtained with wavelength tunable multielectrode lasers and external cavity laser diodes tuned electrically. Potential applications in future systems are also reported, with emphasis put on optical functions such as wavelength switching, bistability and multistability in wavelength.

The arrays of diffusion-stripe monolithic AlGaAs/GaAs lasers with 5, 8, 10, 20 stripes were prepared and investigated. Their light emission characteristics are presented. Power up to 400 mW CW at 293 K and full conversion efficiency 41% were observed from the array of 8 stripes an antiguide regime with 40 microns emitting area. Up to 60% of optical power was coupled to multimode fiber at wavelength 808 nm for applications in Nd:YAG laser-pumping systems.

This report presents some considerations on comparison of subsonic and supersonic chemical oxygen-iodine lasers performance.

Investigations of iodine amplifiers with an aperture of 20...200 cm are presented. It is shown that at the aperture of 200 cm and active length of La equals 720 cm it is possible to extract Ep approximately equals 40 kJ in a monopulse from the amplifier. The results of work can be used at laser fusion facilities for the energy of Ep approximately equals 10⁶ J.

Experimental investigations of inversion formation dynamics in the iodine laser pumped by shock wave front radiation were performed. Vacuum ultraviolet (VUV) radiation presence in the pumping spectrum is shown to cause substantial reduction of the inversion in the region just before a shock wave. A supposition is stated that probable mechanism of this phenomenon is quenching of excited iodine atoms by an unknown substance generated during VUV photodissociation of iodides. The ways of active medium protection against VUV radiation by condensed-matter and gaseous spectral filters are suggested.

VNIIEF have been conducting chemical oxygen-iodine laser (COIL) research since 1982. With successive set-up optimizations, this laser had its power increased by 1986 from 10 mW to lkW and was used as a basis to design a new research set-up of about 4 kW power and about I min continuous operation [2]. COIL is traditionally designed to incoiporate a singlet oxygen generator (SOG), a heat exchanger, a laser volume and a pump out system. The schematic diagram of this laser is shown in fig. I. One of the most important parameters of COIL active medium is its temperature. One may use temperature measurements at various gas flow sections as indications of the gas flow and gas mixing homogeneity, processes kinetics, etc. During operation, alkali-solved hydrogen peroxide cooled down to T=255 is put into SOG. As chlorine gas is bubbled therethrough, singlet oxygen is generated. The oxygen together with water vapor enters the heat exchanger having temperature T= 193 K. While passing through the heat exchanger, the oxygen cools and becomes free of water vapor. The laser volume will have iodine - argon or iodine -nitrogen gas mixtme at T=393 K injected to the singlet oxygen flow. To protect the resonator mirrors, there will be also argon or nitrogen screen made in the laser volume, this being at room temperature. The gas flow has velocity up to I 00 mis in laser volume.

Phase conjugation quality of photodissociation laser with SBS mirror depending on the selection grade of Stokes radiation nonreversed component was studied by experiment. Strehl number for the output beam was found it equaled 0,73 (St equals 0,73). Direction of radiation backward was not worse than accuracy of measurement 3 (DOT) 10^-6 rad.

Approximations for frequency and amplitude of relaxation oscillations are considered both in a common case and for CO₂ laser. Different schemes of frequency stabilization system constructions are analyzed for the laser on base of CO₂ active medium.

It has been found, that the main process, responsible for the frequency shift of hybrid CO₂-electron beam laser generation with a pulse duration of more than 10 microsecond(s) is the thermal self-action of radiation. The possibilities of frequency shift decreasing at the expense of self-action decay by active medium optimization are demonstrated.

Repetitively pulsed iodine laser with Q-switch and controlled by magnetic field spectrum of radiation is studied. The application of the laser in the location system with an optical preamplifier is analyzed.

Results of the investigations of the new passive shutter on the base of yttrium-aluminum garnet activated by vanadium ions (V³⁺) are presented. Wide absorption band (1.2 - 1.4 (mu) ) with maximum on the wavelength 1.34 (mu) corresponds to the electron-vibration transition ³A₂ - ³T₂ of ions V³⁺.

An unstable resonator for a laser based on two Nd:YAG active elements with induced thermal lenses is proposed and investigated. The output beam divergence greater by factor 2 than the diffraction limit is achieved. The radiation power of the laser with the resonator proposed has been obtained 20% below but with the 30 times greater on-axis intensity as compared to the ordinarily used resonator in a commercial laser of a similar type.

Considerable increase in efficiency of counterrunning and corunning SRS has been found in system SRS-element and broad-band electronic-vibrations amplifier medium. The characteristics of SRS-lasers with following SRS-elements: barium nitrate, benzol, nitrobenzol which were pumped by YAG-Nd and YAG-Nd lasers and characteristics of the laser with self- transforming active elements PGW-Nd. The broadband medium LiF with color centers inserted in scheme for amplification of the SRS. The efficiency of the pump transformation to the first Stokes was more than 50%. The results can be explained by resonance on first Stokes frequency occurs in coupling system-SRS-element-broadband amplifier medium.

Coherent energy transfer gives rise to a new peak and dip in the probe gain spectrum that move proportionally with the intracavity injected power, showing that stimulated emission and absorption significantly speed up the semiconductor response.