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The femtosecond pulse quality in a laser system is determined by a non-compensated high-order dispersion and spectral deformation of the amplifier. A dispersive device that modifies the spectral amplitude and phase of the femtosecond pulse should be used to improve the duration of the compressed pulse and suppress the prepulses. The application of acousto-optical dispersive delay lines is considered. Different modifications of delay lines are compared and the types of devices used to shape femtosecond pulses are discussed. Several experimental dispersive delay lines were fabricated and investigated.

In this paper we discuss laser wake field acceleration experiments made at the PEtawatt pARametric Laser (PEARL). Using free 2mm and 5 mm gas jet without preplasma we generated electron beam with energy up to 260 MeV. The charge of quasimonoenergetic beams achieved 300 pC, angular divergence 0.2 degree. The special attention is paid for diagnostics which is adapted for low repetition rate systems with low output parameters stability.

Theoretical investigation of second harmonic generation (SHG) of super intense femtosecond radiation demonstrated that temporal Intensity Contrast Ratio (ICR) of output radiation of petawatt level laser complexes can be significantly increased. The cubic polarization effects in the process give possibility of additional pulse compression. We present experimental results of SHG of radiation with average intensity 2TW/cm 2 in 0.6mm KDP crystal. Theoretical model of linear regime of plane wave instability in mediums with quadratic and cubic nonlinearity is developed and thoroughly discussed. Analysis of small-scale self-focusing suppression methodic is presented. The influence of surface dust to spatial noises generation in SHG process is pointed out.

Optical parametric amplification of broad-band pulses in large-aperture KD*P (DKDP) crystals has been studied in experiment. A procedure of adjusting the amplifier for single-shot operation of a pump laser has been developed. Peak power of compressed signal radiation (pulse duration 45 fs at energy 9 J) was 200 TW. This considerably exceeds the record level obtained so far in lasers based on optical parametric chirp pulse amplification.

200 TW (pulse duration 45 fs at energy 9 J) peak power has been achieved experimentally using a Cr:forsterite master oscillator at 1250 nm, a stretcher, three optical parametrical amplifiers based on KD*P (DKDP) crystals providing 14.5 J energy in the chirped pulse at 910 nm central wavelength, and a vacuum compressor. The final parametrical amplifier and the compressor are described in detail. Scaling of such architecture to multipetawatt power is discussed.

We have experimentally demonstrated the existence of super-broadband non-degenerated phase matching for a signal with a wavelength of 911 nm in KD*P crystal pumped with wavelength of 527nm. Parametric amplification coefficient of more than 10 7 in three cascades is achieved. This resulted in pulse energy 10mJ at the output of third cascade. It is shown that in the KD*P crystal chirped pulses of conventional femtosecond sources (a Ti:Sa laser at 911 nm and a Cr:forsterite laser at 1250 nm) can be amplified up to the level that ensures multipetawatt power after compression.