Ptychography for pulse-to-pulse wavefront sensing at free-electron lasers.

The growing interest in the wavefront of ultra-bright and ultra-short pulses produced by free-electron lasers (FELs) brought to the development of several complementary approaches to characterize them. Ptychography has been proposed as a suitable method to retrieve full high-resolution complex-valued wave functions of FEL beams. We present a ptychography-based approach for the retrieval of wavefronts of individual pulses directly at the sample position and within experimental conditions suited for diffraction experiments. The approach is applicable to the investigation of single-pulse wavefronts for other FEL experiments and is especially advantageous in the case of high-fluence. As ptychography is a lensless technique, this approach can in principle achieve diffraction limit resolution.