Generation of Intense Phase-Stable Femtosecond Hard X-ray Pulse Pairs

TL;DR

This paper reports the generation of intense, phase-stable femtosecond X-ray pulse pairs with sub-10 femtosecond separation, enabling advanced coherent spectroscopy and imaging in the X-ray domain.

Contribution

It demonstrates the creation of highly directional, phase-stable X-ray pulse pairs with high photon counts and femtosecond separation, a novel achievement for X-ray free-electron lasers.

Findings

Produced phase-stable X-ray pulse pairs with over 3 x 10^7 photons

Observed interference fringes indicating phase stability and coherence

Achieved pulse durations around 1 fs with 2-5 fs separation

Abstract

Coherent nonlinear spectroscopies and imaging in the X-ray domain provide direct insight into the coupled motions of electrons and nuclei with resolution on the electronic length and time scale. The experimental realization of such techniques will strongly benefit from access to intense, coherent pairs of femtosecond X-ray pulses. We have observed phase-stable X-ray pulse pairs containing more thank 3 x 10e7 photons at 5.9 keV (2.1 Angstrom) with about 1 fs duration and 2-5 fs separation. The highly directional pulse pairs are manifested by interference fringes in the superfluorescent and seeded stimulated manganese K-alpha emission induced by an X-ray free-electron laser. The fringes constitute the time-frequency X-ray analogue of the Young double-slit interference allowing for frequency-domain X-ray measurements with attosecond time resolution.