Spectral Flux Enhancement of X Rays for Addressing Ultra Narrow Nuclear Transitions,Physical Review Letters

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Spectral Flux Enhancement of X Rays for Addressing Ultra Narrow Nuclear Transitions
Physical Review Letters ( IF 8.1 ) Pub Date : 2024-11-06 , DOI: 10.1103/physrevlett.133.193401
Elena Kuznetsova, Xiwen Zhang, Yuri Shvyd’ko, Marlan O. Scully, Olga Kocharovskaya

Recently, the 1.4 feV ultranarrow nuclear transition at 12.4 keV energy in

45 S c

was resonantly excited for the first time using radiation from the self-seeded EuXFEL laser [Y. Shvyd’ko et al., Resonant x-ray excitation of the nuclear clock isomer

45 S c

, Nature (London) 622, 471 (2023)], establishing

45 S c

as a promising candidate for a future Mössbauer nuclear clock. While this experiment demonstrated a high potential of x-ray free-electron laser sources for resonantly exciting nuclear isomers in the hard x-ray range, it also highlighted a severe limitation in the achievable excitation level caused by their extremely large spectral bandwidth

\sim 1 e V

. In this Letter, we propose a method to enhance the spectral flux of x-ray free-electron laser radiation using a resonant absorber with a longitudinal gradient in the nuclear transition frequency. A portion of the incident pulse can be absorbed into a nuclear collective excitation, and converted back into x-ray radiation by reversing the sign of the frequency gradient. Spectral narrowing and flux enhancement of this re-emitted x-ray field is achieved by using a reversed frequency gradient with a smaller magnitude than the initial one. About a hundredfold of such spectral flux enhancement is feasible in

45 S c 2 O 3

single crystal, rendering a more efficient source for nuclear excitation and facilitating the experimental observation of resonant fluorescence and coherent forward scattering at the 12.4 keV transition, both of which are essential for realizing a nuclear clock.

更新日期：2024-11-06

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