Abstract

The successful operation of x-ray free-electron lasers (FELs) such as SPring-8 Angstrom Compact free-electron Laser (SACLA) in Japan provides novel x-ray sources with great properties: an unprecedented peak brilliance, full transverse coherence, and a duration down to a few femto-seconds, which offer great promise for exploring new scientific possibilities in ultrafast science with hard x rays. A split-delay optics (SDO), which can provide two replica FEL pulses with time delay precisely controlled, enables us to investigate ultrafast dynamics induced by intense x rays in currently unreachable time scale of up to nanosecond. A mirror-based SDO using a geometrical splitter [1] has successfully contributed to the progress on ultrafast measurements with soft x-ray FELs. Usage of a similar SDO for hard x-ray FELs, however, includes some problems such as a small critical angle (i.e., a huge system is required) and strong scattering from the mirror edge. We proposed a SDO based on the Bragg diffraction from Bragg-case FZ-Si(220) crystals, in which an FEL pulse is reflected with a large angle and a high spectral reflectivity. Combination with a focusing mirror system enables to generation of a high power density field while precise tuning of crystal angles is required. Here we present the details of the SDO and requirements for overlapping replica beams.

© 2014 Japan Society of Applied Physics, Optical Society of America