NUMERICAL-ANALYSIS OF SRS CONVERSION OF TERAWATT FEMTOSECOND UV PULSES

The results of numerical modeling of nonstationary forward SRS of femt osecond pulses in molecular dispersive gases are presented. The calcul ations are carried out in one-dimensional two-wave approximation takin g into account self- and cross-action of the pulses. For the first tim e the dynamics of a Stokes pulse build-up and the transformation of it s spectrum and temporal shape during amplification are traced up to th e saturation regime in CH4, NH3, H-2, and SF6. The fundamental role of group velocity mismatch, which determines the velocity of a Stokes pu lse with respect to a pump pulse is revealed. It is shown that there e xists a range of parameters where pulse compression takes place under optimum amplification with drastic sharpening of the leading edge of t he pulse. The parameters of SRS converter based on an oscillator and a two-stage amplifier with beam summation at She second stage are calcu lated. The pumping high-power femtosecond excimer system produces two beams with an energy of 1 J each at the wavelength of 308 nm and pulse duration of 300 fs. The converter provides conversion efficiency up t o 60%, threefold compression of the pulse, prepulse suppression, and s harpening of the leading edge.