An ultrastable hard x-ray attosecond split-delay line

Abstract: We present a novel split-delay line design for generating hard x-ray attosecond pulse pulse pairs. The design introduces an unconventional delay adjustment mechanism, where an x-ray mirror pair rotation was used for adjusting the path length differential between two beam paths. The exit beam pointing stability is guaranteed by the mirror-pair self-compensating geometry, therefore enabling stable continuous delay adjustments. We present a parameter study for this concept covering 5-11 keV photon energies with high efficiency over a delay time coverage window of 20-femstosecond with sub-20 attosecond scanning resolution. Wavefront simulations incorporating realistic mirror parameters demonstrate that the system achieves high throughput and is capable of delivering high-peak-intensity pulses. Attosecond x-ray pump x-ray probe capability enabled by such a delay line is poised to unlock a wide range of hard x-ray nonlinear spectroscopy measurements at sub-femtosecond timescales for the first time.