The process of fourth harmonic generation in multicascade laser installation is experimentally investigated. The operative correction of phase synchronism in nonlinear crystals permits to compensate an installation parameters drift and provides stable radiation conversion to the 4-th harmonic with efficiency 0.4÷0.5 at E4'1O J.The use of UV-radiation instead of Nd-laser IR-radiation in laser plasma heating experiments permits to heat the plasma of great density. The obtaining of powerfiul (1 GW) pulses of UV-radiation with a beam divergence of the order of diffractional one is possible by means of two consecutive frequency doubling of Nd-laser frequency in the KDP crystals. However the effective frequency transformation by nonlinear KDP crystals (NC) requires the stabilization of radiation parameters and the synchronism angle of NC, both of which depend on temperature. We have demonstrated an opportunity of high effective quadruplicating of fundamental radiation frequency (? = 1,06 .t) without long-term stabilization of laser radiation frequency and NC temperature. The influence ofthe laser installation parameters drift has been eliminated by the exact tuning ofNC phase synchronism angle just before the experiment.The laser installation consists of a master oscillator (MO) and a multistage power amplifier (MA). The construction of the MA is based on five silicate glass rods of 45 mm diameter and 680 mm length. Each of them was pumped by four 580 mm length xenon flashtubes. For suppression of self-focusing process the MA contains three vacuum space filters.As the MO a Q-switched single mode laser was used. The active element of the MO was gallium-scandiumgadolinium garnet (GSGG) rod of 3 mm diameter and 50 mm length. Q-switch was produced by a passive shutter based on the LiF crystal with F2 color centers. The diaphragm placed in a resonator provided single transverse mode of the MO generation. The one longitudinal mode generation was reached by means of 1) use an output Fabrie-Perrot selective mirror, 2)use of a Q-switch in the resonator of a MO with the LiF:F2 crystal which also has selective properties'.The pulse duration was 10 ns. Laser pulse had an asymmetric time envelope. The sharp front of the pulse (duration -1 ns) was formed by an electro-optical shutter. The rear side of the pulse was smoother. Its shape was determined by the master oscillator generation kinetics. The MO operated in pulse repetition regime (f 1 Hz), which promoted the high reproducibility of radiation parameters after achievement of a thermal steady-state.Between the MO and the MA an additional GSGG preamplifier was placed, which operated also in a pulse repetition regime. The energy of pulses after this preamplifier (without MA amplification) was sufficient to control exactly the angle position of the KDP crystals just before the laser plasma experiment. This simple control method resulted in the elimination of laser parameters drift influence on the frequency conversion efficiency. After that the MA pumping was switched on. As a resu...
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