We demonstrate a method for femtosecond, phase sensitive detection of optical polarization, using an acousto-optic pulse shaper to create a sequence of up to several hundred phase coherent pulses. Essential to this method is the ability of the acousto-optic pulse shaper to update the phase relation of the pulses in the sequence on a nanosecond timescale. The method is demonstrated by measuring the optical free induction decay’ of rubidium vapor, and can be particularly useful for experiments involving very low or very high optical densities. It can easily be extended to multidimensional spectroscopy.
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