Sub-Angstrom Cavity Stabilization of an X-ray Free-electron Laser Oscillator and Metrology with Nuclear Resonance
Highly coherent laser-light sources have proved to be indispensable in precision metrology and fundamental physics. X-ray sources have always lagged behind those on the eV scale in terms of coherence and stability.
The concept of an x-ray free-electron-laser oscillator (XFELO) [1-3] will go a long way towards providing longitudinal coherence within each pulse. With additional sub-angstom stabilization of the recirculating cavity, the XFELO can achieve pulse-to-pulse coherence. An ideal reference for this stabilization can be found in nuclear resonances, such as the 5-neV-wide resonance (140-ns lifetime) at 14.4 keV in 57Fe. An XFELO stabilized in this way can come close to rivaling state-of-the-art atomic clocks.
Other isotopes, especially 45Sc may lead to 6-8 orders of magnitude improvement, opening new possibilities in metrology and fundamental physics. The talk will present the concept of the XFELO, the stabilization, proposed metrology applications, and fundamental science such as studies of quantum decoherence and quantum gravity.
 Kwang-Je Kim, Yuri Shvyd’ko, and Sven Reiche, A Proposal for an X-Ray Free-Electron Laser Oscillator with an Energy-Recovery Linac, Phys. Rev. Lett. 100, 244802 (2008)
 Kwang-Je Kim and Yuri V. Shvyd'ko, Tunable Optical Cavity for an X-Ray Free-Electron-Laser Oscillator, Phys. Rev. ST-AB 12, 030703 (2009)
 B. W. Adams and K.-J. Kim, in preparation