Phase-sensitive femtosecond time-resolved four-wave mixing with spatial light modulators

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Phase-sensitive femtosecond pulse shaping apparatus has been constructed using a liquid crystal spatial light modulator (SLM) with is commercialized for use in projectors. The SLM was an active-matrix TFT twisted nematic liquid crystal SLM with 640x 480 pixels, each of which can be controlled independently by a personal computer in 256 greyscale. A Michelson interferometer was built for the measurement of the amplitude and phase change of the light transmitted through the SLM at each of the 256 levels. Mask patterns and the generated waveforms were calculated by a newly written simulated annealing computer program which incorporated the experimentally obtained amplitude-phase relation. An interferometric cross-correlation measurement apparatus was constructed which used two-photon-induced current in a GaAsP photodiode. God quality of data was obtained when the path length was modulated by a piezo-electric actuator. Another cross-correlation measurement technique using two- photon-induced photocurrent in a photomultiplier tube has also been developed. Measurements of the generated waveforms using the technique described above have confirmed the ability of the constructed pulse shaping apparatus. Phase control of the generated waveforms was also performed.