Adaptive shaping of high-power broadband femtosecond laser pulses

We demonstrate the implementation of a feedback controlled pulse shaping device in a femtosecond high-power Ti:sapphire laser system. The laser system consists of a mirror dispersion controlled oscillator and a multipass amplifier with a pairing double prism compressor. The system provides pulses with a duration of 30 fs and an energy of up to 1.2 mJ per pulse at 1 kHz repetition rate. The phase distorted output pulses are phase modulated with a high resolution spatial light modulator (SLM). The pulse shaper consists of an all-reflective zero-dispersion compressor equipped with a liquid crystal array. For adaptive compression of the amplified pulses a feedback loop is implemented. A two-photon process is used to monitor the temporal pulse characteristics. To achieve the shortest possible pulse an evolutionary algorithm controls the pulse shaper utilizing the two-photon signal as feedback. With this set-up transform limited pulses are achieved. Detailed investigations of algorithm parameters and their effect on convergence behaviour have been performed and are compared with the experimental findings.