High-order harmonic pulse broadening in an ionizing medium

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Abstract
High-order harmonic pulse durations are measured using a laser and vacuum ultraviolet cross-correlation technique and the results are compared to theory. Harmonic pulses generated using moderate laser intensity are well described by current models and demonstrate that harmonic pulses are temporally broadened when produced at laser intensities sufficiently high to ionize the medium. At even higher generating laser intensity, measured pulse durations are longer than simulated pulse durations. We consider dipole emission from ions and distortion of the spatial laser profile as possible causes for the discrepancy.