Exploring the wavefront of hard X-rayfree-electron laser radiation

摘要

The high photon flux and femtosecond pulse duration of hard X-ray free-electron lasershave spurred a large variety of novel and fascinating experiments in physical, chemical andbiological sciences. many of these experiments depend fundamentally on a clean, welldefined wavefront. Here we explore the wavefront properties of hard X-ray free-electron laserradiation by means of a grating interferometer, from which we obtain shot-to-shot wavefrontinformation with an excellent angular sensitivity on the order of ten nanoradian. The wavefrontdistortions introduced by optical elements are observed in-situ and under operationalconditions. The source-point position and fluctuations are measured with unprecedentedaccuracy in longitudinal and lateral direction, both during nominal operation and as the X-rayfree-electron laser is driven into saturation.