Measurement of High Harmonic Pulse Durations Via Laser Assisted X-Ray Photoionization

Abstract

Ultrashort x-ray pulses are powerful diagnostic tools, combining the temporal resolution typically reserved for optical (laser) pulses with atomic scale spatial resolution which, in principle, can be achieved using high energy electromagnetic radiation. Progress in the development of femtosecond x-ray sources has been hindered by an inability to measure x-ray pulses of femtosecond duration. Streak cameras are typically used to measure ultrashort x-ray pulses, however the ~1 ps resolution limit of these instruments abates their usefulness in the femtosecond regime. We report use of a visible/x-ray cross correlation technique, based on laser assisted x-ray photoionization, to measure 50 fs soft x-ray pulses. The technique permits direct measurements on the duration of femtosecond high order harmonic radiation. We find that harmonic pulse durations are determined by the spatial and temporal profile of the generating laser pulse.