<title>Stretcher-compressor design for OPCPA system with chirp reversal</title>

Abstract

A prismlgrating aberration-free stretcher for OPCPA system with chirp reversal is presented. A designed stretcher with a conventional grating compressor allows to accurately compensate the residual dispersion of the system up to the 4-th order inclusive. The peak power of200 TW in the 45-fs pulse at the output ofthe OPCPA laser was achieved. ThTRODUCTIONThe fruitful idea of chirped-pulse amplification (CPA) [1] is used practically in all extra-high-power laser systems generating super-short pulses terawatt, multi-terawatt, sub-petawatt and petawatt level of peak power. The principle scheme of CPA is presented in Fig. 1. Seed pulse of low-power radiation from femtosecond master oscillator is chirped in a stretcher. Here its duration increases up to hundreds of picoseconds that allows to amplify energy of a pulse up to tens and even hundreds of joules without undesirable effects of self-focusing and optical breakdown. Then this amplified pulse is compressed up to initial duration and, thus, gets huge values of peak power.By present time the peak power petawatt level has been reached only on four laser systems [2][3][4][5];however all over the world there is a number of projects aimed to the creation of petawatt laser systems. In operating and in projected systems, Nd:glass or Ti:Sapphire are used or planned to be used as the amplifying medium of final stages. Fig. 1. The principle scheme of CPA method.In the mid-90-s for receiving of super-power laser radiation it was offered to use optical parametric chirpedpulse amplification (OPCPA) [6,7]. The basic OPCPA scheme is very similar to CPA one (see Fig.1), only here parametric amplification in nonlinear crystals is used instead of laser amplification in active elements. However, for an achievement of petawatt power, nonlinear crystals with the big aperture are required. In this connection, in developed super-power OPCPA-systems KDP crystals which aperture can reach 20-30 centimeters are considered as amplifying elements.Nonlinear crystals stable to laser radiation possessing a large value of nonlinear coefficients (first of all BBO and LBO) are used in the first stages of hybrid type systems [8] including both parametric and laser amplifiers. In some of them the conversion of signal wave to the conjugated (idler) one is used and then, in the subsequent stage, return conversion to initial wavelength of signal radiation is carried out. Such "maneuver" allows to raise essentially contrast of intensity of output recompressed pulse.It is important to note, that in all listed CPA, OPCPA and hybrid systems (we shall name them traditional CPA systems) the wavelength of stretched and recompressed radiation is the same (see Fig. 1) and corresponds to the wavelength of a femtosecond master oscillator. Thus, conditions of the phase matching of a stretcher, an amplifier and a A A

Compact 0.56 Petawatt laser system based on optical parametric chirped pulse amplification in KD*P crystals

“…We used an original stretcher, which incorporates a prism pair between the diffraction gratings [20,22]. For a certain choice of parameters (see details in [28,29]) this stretcher allows efficient pulse compression at a wavelength of 910 nm after OPA using an ordinary grating compressor. The stretcher having a transmission band of 1000 cm −1 expanded the pulse duration up to 600 ps.…”