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Generation of multi-millijoule red-shifted pulses for seeding stimulated Raman backscattering amplifiers.

The efficient generation of redshifted pulses from chirped femtosecond joule level Bessel beam pulses in gases is studied. The redshift spans from a few 100 cm⁻¹ to several 1000 cm⁻¹ corresponding to a shift of 50-500 nm for Nd:glass laser systems. The generated pulses have an almost perfect Gaussian beam profile insensitive of the pump beam profile, and are much shorter than the pump pulses. The highest measured energy is as high as 30 mJ, which is significantly higher than possible with solid state nonlinear frequency shifters.