Cavity stabilization of an x-ray free-electron laser oscillator and metrology with nuclear resonance
by
Bernhard W. Adams(Advanced Photon Source, Argonne National Laboratory, Lemont / USA)
→
Europe/Berlin
Building 25 b / Room 109
Building 25 b / Room 109
Description
An x-ray free-electron laser oscillator (XFELO) [1,2] will use highly reflective backscattering crystals and grazing-incidence mirrors to form a recirculating cavity and produce a sequence of intense, coherent hard x-ray pulses.
A scheme is proposed [3] to stabilize the cavity length by making one of its longitudinal modes stay on a nuclear resonance, such as that of 57Fe.
With a typical longitudinal mode spacing 15 neV and an inhomogeneously
broadened 57Fe resonance of 10 neV, a feedback signal can be obtained
with sufficient contrast.
An application of this device is a measurement of the nuclear-resonant
wavelength relative to optical length standards to an accuraccy of 10^-11, and possibly better.
To that purpose, the output of this stabilized cavity is back-reflected into itself to produce a standing wave, which is probed by 57 nuclei embedded into a thin crystal of a matching lattice spacing. This crystal is moved along the standing-wave pattern under optical interferometric control, and the resonance fluorescence from the nuclei is monitored.
With a tight focusing, the number of probing nuclei could even be
reduced to one. With existing knowledge of the wavelength, sparse probing of the standing wave can be applied to drastically reduce the data acquisition time.
Extensions of this method to longer-lived nuclei, such as 181Ta, can further improve the accuracy.
Applications may be found in fields from metrology at atomic length scales to tests of quantum gravity. With further developments, the accuracy the scheme could surpass that of optical time/length standards.
[1] Kwang-Je Kim, Yuri Shvyd'ko, Sven Reiche, Phys. Rev. Lett. 100,
244802 (2008)
[2] Kwang-Je Kim, Yuri Shvyd'ko, Phys Rev. ST-AB 12, 030703 (2009)
[3] Bernhard W. Adams, Kwang-Je Kim, manuscript in preparation
