Abstract

We demonstrate intensity autocorrelation techniques to directly characterize the pulse duration of hard x-ray free-electron laser (XFEL) pulses. A bottleneck for the realization of the technique is insufficient intensity of XFELs propagating through currently available autocorrelators, which employ silicon perfect crystals that work as a monochromator with a bandwidth of much narrower than typical XFEL bandwidths. Thanks to the self-seeding amplification mechanism, the spectral brightness of XFELs is increased and the XFEL intensity after the crystal-based autocorrelator reaches ~10¹⁷ W/cm² at a micrometer-scale focal spot size, making the intensity autocorrelation techniques possible for hard x-ray lasers.

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