Use of KD*P crystals for non-degenerated broadband optical parametric chirped pulse amplification in petawatt lasers

The problem of creating optical parametric amplifiers of femtosecond pulses up to the multiterawatt level was fiist discussed in [l, 21. In these papers, as well as in subsequent studies [3-91, only nonlinear elements made from KDP crystals, whose aperture can be as great as 30cm, were considered as nonlinear elements for final cascades of optical parametric amplifiers (OPAs). The most promising pump source is the second harmonic of a Nd:glass laser with a wavelength of 3L3=527nm. At this pumping, the KDP crystal has two serious disadvantages: it absorbs greatly at wavelengths higher than 1200nm and has maximal gain bandwidth (1000-1200~m~[l~]) at the wavelength of signal 1050-1 1 OOnm, i.e., at degenerated (or nearly degenerated) phasematching. In this wavelength range, however, it is difficult to create light sources with pulse duration of less than 50fs.