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Ellipsoidal laser pulses with central wavelength of 1030 nm and duration of 40 ps were obtained. It is expected that after conversion into the fourth harmonic this will reduce appreciably emittance of the electron beam, injected by the laser.

Thermal effects in optical mediums became more and more important in applied optics because of quick and steady grow of average power of modern lasers. Radiation power is so high that phase distortions caused by thermal lensing effects became important for achieving lasers resonators stability. In this paper we discuss interesting experimental results for YLF crystal: high anisotropy and high astigmatism of thermal lens in acutted YLF rods. The first effect is more or less predictable because YLF is uniaxial crystal. But high astigmatism of thermal lense is unexpected and is not explained in literature so far. Astigmatism is so high that phase distortions profile for perpendicular directions can change its sign [1–3]. Unfortunately in most papers the reason of thermal lens astigmatism is not discussed. At some papers there is a try to explain this by thermal conductivity anisotropy and as a result - non-symmetric temperature distribution but this effect is unable to change the sign of the lens.

In struggle for record average and peak power of laser radiation it was found out that many characteristics before used materials don't answer increasing inquiries. There was a problem of searching new alternative materials. One of such materials can be a ceramic. For lasers with high average and peak power a polycrystalline ceramics offers well-known advantages: large aperture like in glass, high thermal conductivity like in single crystals, higher than in single crystal thermal shock parameter, possible control of spectroscopic characteristics and low cost. Recently, 67kW CW ceramics laser was reported. At such power the important role is played by the thermal effects which studying in ceramics becomes actual. In this paper, we present a theoretical model of thermal effects in laser ceramics and their experimental confirmation.

Positive thermal lens in optical element (Faraday isolator in our case) produced by absorption of high power radiation was experimentally compensated with negative thermal lens in DKDP sample self-adaptive to different radiation powers.