Large aperture stretchers for high intensity laser systems

The paper presents analysis results of large aperture stretcher schemes for use in laser systems after pre-amplification stages. To increase output peak power in the two-channel femtosecond laser system with coherent field combining, developed at ILP SB RAS, a stretcher for deployment in front of additional amplification stages is required. The stretcher and additional stages will boost pulse energy in a channel up to 1.5 J. Since beam energy at stretcher input is 100-150 mJ, beam diameter exceeds 20 mm what, is determined by damage thresholds of stretcher elements. With a stretching ratio of 10 and such an aperture, aberrational distortions of the stretcher obstruct further compression, focusing, and effective coherent combining of amplified pulses. Optimized parameters of the off-axis and off-plane Offner stretchers allow pulse stretching to 2.1 ns (spectrally limited duration ~20 fs and carrier wavelength 0.83 μm) and subsequent recompression down to 24 fs and 35 fs in a beam with 20 mm aperture.