FEL2012 - List of Authors (Adams, B.W.)

Paper	Title	Page
WEPD31	Sub-Ångström Stabilization of an X-ray Free Electron Laser Oscillator and Nuclear Resonance Metrology	437
	B.W. Adams, K.-J. Kim ANL, Argonne, USA
	Funding: This work was supported by the U.S. Department of Energy, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357. A scheme is described to length-stabilize the cavity of an x-ray free-electron-laser oscillator (XFELO)* by keeping one of its longitudinal modes in nuclear resonance at 14.4 keV with a sample of ⁵⁷Fe. The mode spacing corresponding a 100 m XFELO cavity is about 12 neV, which can be resolved with the 5 neV linewidth of ⁵⁷Fe, even with some inhomogeneous line broadening. With a cavity thus stabilized, a standing-wave pattern can be maintained over hours, to be probed by another sample of ⁵⁷Fe in a meter-long scan to compare the nuclear-resonant wavelength with a known optical standard. This should improve the relative accuracy of this wavelength from 10^-7** to 10^-11. Ensemble, or long-time averaging, as used in atomic clocks, can further increase the accuracy. Refining the scheme to other nuclear-resonant species with narrower resonances, such as ¹⁸¹Ta (6.2 keV, 75 peV), will open up precision x-ray metrology for technological and fundamental applications. * K.-J. Kim, Yu. Shvyd'ko, S. Reiche, Phys. Rev. Lett. 100, 244802 (2008);K.-J. Kim, Yu. Shvyd'ko, Phys. Rev. ST-AB, 030703 (2009) ** M. Lucht, dissertation, Hamburg (2005)

Paper

Title

Page

Sub-Ångström Stabilization of an X-ray Free Electron Laser Oscillator and Nuclear Resonance Metrology

437

B.W. Adams, K.-J. Kim
ANL, Argonne, USA

Funding: This work was supported by the U.S. Department of Energy, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.
A scheme is described to length-stabilize the cavity of an x-ray free-electron-laser oscillator (XFELO)* by keeping one of its longitudinal modes in nuclear resonance at 14.4 keV with a sample of ⁵⁷Fe. The mode spacing corresponding a 100 m XFELO cavity is about 12 neV, which can be resolved with the 5 neV linewidth of ⁵⁷Fe, even with some inhomogeneous line broadening. With a cavity thus stabilized, a standing-wave pattern can be maintained over hours, to be probed by another sample of ⁵⁷Fe in a meter-long scan to compare the nuclear-resonant wavelength with a known optical standard. This should improve the relative accuracy of this wavelength from 10^-7** to 10^-11. Ensemble, or long-time averaging, as used in atomic clocks, can further increase the accuracy. Refining the scheme to other nuclear-resonant species with narrower resonances, such as ¹⁸¹Ta (6.2 keV, 75 peV), will open up precision x-ray metrology for technological and fundamental applications.
* K.-J. Kim, Yu. Shvyd'ko, S. Reiche, Phys. Rev. Lett. 100, 244802
(2008);K.-J. Kim, Yu. Shvyd'ko, Phys. Rev. ST-AB, 030703 (2009)
** M. Lucht, dissertation, Hamburg (2005)