A new class of high power solid state lasers on neodymium containing media with passive Q- switches on LiF:F2- crystals was investigated. The generation regimes and the technological possibilities of such lasers were studied.

The paper treats the problems of growth of large defectless single crystals of gadolinium- gallium garnet (GGG) doped with chromium, cerium, and neodymium, up to 65 mm in diameter and 130 mm long. The influence of UV radiation of the pump flashlamp on the formation of stable color centers in GGG-crystals co-doped with Cr, Ce, and Nd-ions was investigated. The processes of a nonradiative energy transfer from Cr to Nd ions in GGG were analyzed. The lasing properties of the GGG:Nd and GGG:Cr,Ce,Nd crystals were studied at 4F3/2 yields 4I11/2 and 4F3/2 yields 4I13/2 transitions. On the basis of grown crystals efficient lasers with the wavelengths of 1.06 and 1.33 micrometers are developed.

High power solid state lasers in the range of kW average output are of interest for applications in material processing. Especially the transmission of power up to 2 kW by fibers makes these systems fascinating. A review on the state of the art is given and the different approaches to high beam quality lasers (multirod, slabs, tubes) are discussed.

Basic problems related to crystals growing and material science of rare-earth scandium garnets (RESG) are considered from the point of view of their applications in solid-state lasers. Special concern is dedicated to solid solutions of scandium garnets combining positive qualities of both aluminum and gallium RESG. The role of chromium impurity in garnets, which has great and versatile influence on the growth of crystals as well as on their physical properties and lasing characteristics, is discussed. Mechanical, thermophysical, optical, spectroscopical, and other properties of rare-earth scandium garnets are considered.

Lasers of 3 micrometers range on YAG:Er and YSGG:Cr,Er crystals were studied at similar experimental conditions. The results of the comparative investigations are presented.

Processes of interaction of excited ions are investigated in several laser crystals: Er-Er -- in YSGG:Cr, Er and GSAG:Cr,Er crystals; Ho-Ho -- in YSGG:Cr, Ho crystals; Tm-Tm -- in YSGG:Cr,Tm and YAG:Cr,Tm crystals; Tm-Ho -- in YSGG:Cr, Tm, Ho and YSAG:Cr, Tm, Ho crystals; Cr-Cr -- in 11 of different laser crystals (ruby, YAG, GSGG, YSGG, LICAF, et al.); Cr-TR (Er, Ho, Tb, Tm, Nd, -- TR) in YAG, YSGG, GSGG, GSAG crystals.

Results of spectroscopic and radiation investigations of disordered calcium-niobium-gallium garnets (CNGG) with wide inhomogeneously broadened lines in absorption and luminescence of Nd3+ are presented. A method of a selective and frequency tuned laser excitation at T equals 77 K provided discovery of four groups of optical centers and development of Stark multiplet 4F3/1 and 4I9/2 levels schemes for these centers. Laser excitation at the 4I11/2 yields 4F3/2 transition at T equals 300 K during time resolved luminescence spectra recording at the same transition resulted in discovery of an inhomogeneous character of amplification spectrum broadening as well as in estimation of spectral energy migration among the centers. This time it was found to be longer than the 4F3/2 level lifetime (150 microsecond(s) ec). Results of the investigation of free-generation and passive mode-locking regimes in lasers based on disordered garnets with neodymium are presented. It is shown that energy parameters of the lasers based on CNGG are higher than those of glass lasers. In the passive mode-locked regime pulses are generated with (lambda) equals 1.06 micrometers and duration time 5 - 7 psec. The pulses have positive linear frequency chirp and spectrum broadening up to 60 cm-1. Compression of the chirped pulses in an external compressor provides transfer to femtosecond time scale.

Trains of stable reproducible picosecond light pulses were obtained with a laser on the neodymium ions activated potassium-gadolinium tungstate single crystal, using stationary passive mode-locking technique. A single cavity-dumped pulse of not more than 5 psec duration was amplified up to approximately 10 mJ under repetition rate about 1 Hz in a wide- aperture active element made of the same material.

Using the spectroscopic data obtained, the possibility of producing stimulated generation in doped solid state media -- beryllium aluminates doped by 3-D-ions (Ti3+, V4+, V3+, Ni2+, Cr3+) -- is considered and a series of emission parameters of Ti and Cr ions is presented.

The criteria-characteristics of glasses for active and passive laser components in respect to their thermomechanical, beam strength, and thermo-optical properties are analyzed. The perspectives and the ways of developing glasses with extremal strength and thermo-optical properties are considered. The parameters of new glasses are presented.

Two types of YSGG:Cr, Nd-lasers were investigated. The use of an opto-mechanical modulator in one of them and of a polarization-closed cavity in the other made it possible to achieve the efficiency of 3 - 4% with the output energy up to 460 mJ and the pulse repetition rate up to 50 Hz. Laser efficiency at the second harmonic wavelength was 1.5 - 2%, the frequency being converted in the KTP-crystal. The prospects of further growth of the output parameters were analyzed for such lasers.

We present the results of investigations of nonlinear absorption in alkaline-earth fluoride crystals containing divalent neodymium ions, and also the results of utilizing these crystals for passive Q-switching and mode-locking in solid state lasers radiating in the wavelength range (1.3 - 1.6) micrometers . Spectroscopic parameters of the studied materials such as the effective absorption cross-section and the relaxation time of the state of self-induced transparency (SIT) were estimated. The nature of the residual absorption was determined in these crystals and a simple spectroscopic model describing the SIT process in MeF₂:Nd²⁺-crystals is offered. It is demonstrated that MeF₂:Nd²⁺-crystals can be used as Q- switches for the lasers of the near IR wavelength range. The results of Q-switching of neodymium and erbium lasers generating in the ranges of 1.3 and 1.54 micrometers , respectively, are presented. The single-peak generation regime and generation of a train of modulated pulses are investigated. The use of SrF₂:Nd²⁺-crystals allowed us to realize the mode-locked regime in YAG:Nd-crystal laser, operating on the transition ⁴F_3/2 yields ⁴I_13/2. Evaluation of the duration of peaks gives the time less than 400 psec.

Hidden spatially periodic oscillations of energy absorption by orientation groups of anisotropic quantum systems in birefringent crystals were calculated. Conditions favoring experimental detection of modulation phenomena were determined, and their features have been studied under nonstationary excitation by ultrashort light pulses.

New active media for near IR cw tunable lasers based on F₂⁺O^2- color centers in additively colored crystals NaCl, KCl, KBr, RbCl doped with hydroxide ions OH^- were studied. The optimal conditions of these centers formation were determined. The generation characteristics of cw lasers based on F₂⁺-centers in LiF, TL⁰(I)-centers in KCl:TI, F_A(II)-centers in KCl:Li, and F⁺O^2--centers in crystals NaCl:OH, KCl:OH are presented.

The results are presented of theoretical and experimental studies of two-step photoionization and photochemistry of color centers in LiF crystals. The exact analytic expressions were obtained for the population of optic centers energy levels in the process of two-step photoionization within a framework of kinetic equations in three-level approximation. A transfer from cw to pulsed-periodic excitation was analyzed. An analytic dependence was obtained of the ionization cross-section on the incident light flux intensity. For the first time the cross-section was estimated of the photoionization from the excited level of F₂ color center in LiF crystal being pumped by 532 nm wavelength radiation. The processes were detected of mutual phototransformations of F₃, F₃⁺ and N color centers in oxygen-free LiF crystals. It was demonstrated that the presence of F₃ and F₃⁺ color centers in crystals is necessary for selective accumulation of N color centers at high temperature (300 K) action of Nd:YAG laser third harmonic radiation. In LiF- OH crystals the processes of mutual phototransformations were detected in a CC ensemble with absorption bands maxima at wavelengths 380 nm, 450 nm, and within the range 500 - 570 nm. It was demonstrated that an effective destruction of the CC absorption band (380 nm) along with the formation of absorption bands with maxima within 500 - 570 nm takes place under high-temperature (300 K) action of Nd:YAG laser third harmonic radiation ((lambda) equals 354 nm). Reverse phototransformation with the recovery of the band at 380 nm takes place along with the known phototransformation F₂ (450 nm) yields F₂⁺ (654 nm) under the subsequent action of the same laser second harmonic radiation ((lambda) equals 532 nm).

Passive laser Q-switches on the basis of crystals of LiF with F₃^-- and LiF with F₃^--like centers, and LiF:O, OH with new F₂⁺-like centers were investigated. The paper presents power characteristics and radiation parameters of alexandrite lasers with different Q-switches. Operating potentials of Q-switches are determined.

Spectroscopic characteristics, type, and orientation of elementary oscillators for color centers with phonon-deficient lines at 0.93 and 1.077 micrometers were determined. Passive laser shutters with controllable initial transmission for erbium ((lambda) equals 0.85 micrometers ) and neodymium ((lambda) equals 1.064 micrometers ) lasers were developed and tested.

We present the results of the experimental study of laser-induced absorption (LIA) in KTiOPO₄ crystal (KTP) under the action of laser radiation of wavelengths 0.37 - 0.44, 0.53, and 0.68 - 0.88 micrometers . New data are obtained on the nature of the color centers in KTP. The relationship is established between the LIA effect and laser damage threshold of the crystals. The influence is outlined of the LIA effect on the process of frequency doubling in KTP crystal.

Efficiency of conversion to second harmonics of the radiation at (lambda) equals 1079 nm from the rubidium titanil phosphate crystal and of conversion to high harmonics on BBO crystals is investigated.

P-p'-dioxydiphenylsulpfone, p-nitro-p'-methylbenzylidenaniline, 3-metoxy-4- oxybenzaldehyde crystals are obtained of high optical quality. Refraction index dispersion, nonlinear susceptibility tensor components values, and symmetry classes are determined. It is shown that the crystals posses high nonlinear susceptibility along with a wide range of transparency and high laser damage threshold. A new method of nonlinear susceptibility measurements is considered.

Crystals Ral₃(BO₃)₄ (R equals Y, La and lanthanoids), (beta) -BaB₂O₄, and LiB₃O₅ serve for laser radiation conversion from ultraviolet to mid-IR. The process of their flux crystallization is limited by a specific process for each material. In the case of RAl₃(BO₃)₄ it is the separation of the BO₃-triangles. For (beta) - Ba₂O₄ the limiting factor is the formation of isolated threefold rings B₃O₆. Finally, regrouping of three-dimensional polymers limits the crystallization of LiB₃O₅. These processes are usually accompanied by the change of coordination number of B from 4 to 3 and vice-versa. For YAl₃(BO₃)₄ the growth activation energy is as much as 335 kJ/mole. For crystal growing, the limiting concentration of borates are: 20 - 30 wt% (system RAl₃(BO₃)₄- K₂Mo₃O₁₀ - R₂O₃ - B₂O₃), 59 wt% (NdAl₃(BO₃)₄ - BaO (DOT)2Ba₂O₃), 77.5 mol.% (BaB₂O₄ - Na₂O), and 97 mol.% (LiB₃O₅-B₂O₃).

A dislocation model is proposed on the basis of the experimental data, observed for the first time, of photorefractive effect in the DKDP crystal below room temperature. It is shown that a similar effect can be expected in a rather wide class of crystalline materials with well pronounced piezoelectric and electro-optic properties.

Frequency locking of diode pumped YAG lasers to high finesse interferometers is discussed. Relative stability at the sub-Hz level is demonstrated and application of this work to the generation of mmwave radiation to 1 15 GHz for high speed photodetector characterization is presented. 1.

This paper presents the experimental results on the intracavity adaptive correction of the thermooptical phase distortions in the pulsed YAG-laser. Average 3-times increase in the beam axes intensity has been achieved with only 10 loss in the total output laser pulse energy. The system stability to variations of the thermooptical distortions has been demonstrated. 1 .

Nonstationary processes in multi-axial-mode solid-state lasers caused by combination mode coupling (fourwave mixing) were investigated in theory and experiment. The role of frequency nonequidistancy of the mode spectrum was analysed. Routes to chaos and instability character have been studied both for free-running generation and for the case of intracavity second harmonic generation ( " green problem " ). 1 .

Using a conceptual designing technique developed we evaluate the feasibility of laser diode pumped solid state laser systems which have 1OMJ blue output 10 overall efficiency and 10Hz repetition rate with typical solid state laser materials for the reactor driver from both technical and economical points of view. For an economical laser fusion reactor driver the solid state laser materials are required to have the following properties hw/a 40J/cm2 (hco : the laser photon energy a : the stimulated emission cross section) a thermal shock parameter of ≤3W/cm a nonlinear index of refraction smaller than --3x1013 esu and a fluorescence lifetime of ≤4ms. 1.

Erbium-doped glass lasers operated near by 1 5 mm wavelength are helpful for medicine and biology optical communication and eye-safe range finder systems. Advances in erbium-doped glass especially phosphate glass and lasers based on it have been extensive in recent years. Nowadays we can approve that erbium glass lasers are not worse compared with the neodymium ones by many spectroscopic and laser properties. Developments of the energy spectral and temporal characteristics and tuning near the 1500 nm wavelength of the erbium - doped phosphate glass lasers are reported. 2. SPECTROSCOPIC PECULIARITIES OF THE ERBIUM DOPED GLASS Phosphate erbium-doped glass possess a number of spectroscopic peculiarities as a laser active medium. Energy level diagrams of Er3 ions and two other its co-doped ions -Yb3 and Cr3 and the actual transitions (radiate and nonradiate) between them are shown in Fig. 1 (a). Absorption spectrum of that phosphate glass is also shown in Fig. 1 (b) . One can see that the whole pum energy is absorbed only by coactivators - Yb Cr - Yb E r and Cr3 - and then quickly and efficiently transferred from them to Er3 ions. Thus ''7 lasing and pumping of the erbium glass are ''4 realized by means of quite different ions. 4 Thanks to that one can get a low laser threshold t1/2 usin a small doping of Er3 ions (about 1019 I3/2 cm ) and the same time have a high efficient 4T pumoing by using the big concentration of ions 15/2 Yb3 and Cr3 in them (1021 cm3 and 1020 b cm3 accordingly). Obstacles for high efficiency of the lasers may be connected with either increase of the back pump energy transfer from Yb3 ions to Cr3 ones by too large concentration of Cr3 ions or thermal distortions of the active medium. Optimal pumping conditions for lamp pumped Er - doped glass laser differ from neodymium ones. It is explained by the important role of pump energy transfer processes in Er - doped glass. In order to have of high efficient pumping it is necessary that energy transfer rates from Yb3 to Er3 - 3+ 3+ WybEr and from Cr to Yb - WCrYb would be a lot of more then pumping rate W p (mainly object to WYbEr W1). It means the need to use pump pulse durations of about 1O - 102 s and more in that lasers. 3. EFFICIENCY AND THERMAL DISTORTIONS IN THE LASERS Efficiency of the lamp pumped Cr - Yb - Er doped phosphate glass oscillator can be up to 3 or some more (slope efficiency is up to 3. 5 ) /1 at free - running operation and storage efficiency of amplifiers based on the glass can be up to 1. 2 / 3 /. It was achieved

A new concept of high peak power solid state laser system on the basis of successive amplification of a relatively long pulse (5O-l5Ons) and its effective compression by stimulated Brillouin scattering (SBS) is discussed. Analyses and experiments indicate that the energy fluence for long pulses can be significantly increased. Such laser system can be more effective more simple and less expensive than traditional master oscillator-power amplifier (MOPA) geometry.