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

Proceedings of the National Academy of Sciences of the United States of America 119(12), e2119616119 (2022). doi:10.1073/pnas.2119616119
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 than 3*107 photons at 5.9 keV (2.1 ��) with ~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�� emission induced by an X-ray free-electron laser. The fringes constitute the time-frequency X-ray analogue of Young���s double-slit interference allowing for frequency-domain X-ray measurements with attosecond time resolution.
Published by National Acad. of Sciences, Washington, DC