Adaptive compression of intense 250-nm-bandwidth laser pulses
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Self-phase modulation produced by propagation of a 50-fs laser pulse in a hollow-core fiber capillary filled with argon gas was used to broaden the bandwidth from 30 nm to 250 nm. A subsequent compressor utilizing a pair of gratings and cylindrical optics compressed the pulse to 12.5 fs. A liquid-crystal spatial light modulator (SLM) was placed in the compressor, and an evolutionary algorithm based on feedback from the second-harmonic signal was used to control the SLM and optimize the pulse duration. The algorithm increased the second-harmonic signal by a factor of two, indicating that it has substantially improved on the 12.5-fs pulse duration.