本工作表明將原子核樣本放置在X光錐形波導的焦點處，聚焦的 X 光自由電子雷射(XFEL)可以產生同調地產生瞬時原子核居量反轉。用高原子序的包覆材料(如鉑)所製成的橢圓X光波導管可以聚焦X光使其強度比入口端大800倍左右。此功能可用於驅動原子核Mössbauer躍遷並達到原子核瞬時居量反轉。本工作還證明儘管在XFEL相干時間≤10fs 的參數區域中，仍可產生高達約 2×10^5 顆原子核處於激發態。此結果展示了錐形波導在 X 光量子光學領域中的重要作用。本工作和製造gamma射線雷射或原子核電池的應用息息相關。
This work show that transient nuclear population inversion can be coherently generated by a focused x-ray free electron laser pulse in a tapered waveguide where a nuclear sample is placed at the focal point.
We theoretically show that elliptical waveguides using a cladding material with a high atomic number, such as platinum, can maintain an x-ray intensity of up to three orders of magnitude larger than in free space. This feature can be used to place a nuclear sample in the waveguide focal area and drive nuclear Mössbauer transitions up to transient nuclear population inversion. The latter is a long-standing goal related to gamma-ray lasers or nuclear state population control for energy storage. We show that inverted nuclei numbers of up to approximately 2×10^5 are achievable in the realistic region of longitudinal x-ray-free-electron-laser coherence time ≤ 10fs. Our results anticipate the important role of tapered x-ray waveguides and strategically embedded samples in the field of x-ray quantum optics.
Figure. (a) Axial x-ray intensity for 14.4~keV x-ray propagation in a Pt-cladding elliptical waveguide (EWG). (b) Spatial distribution of 57Fe nuclear inversion (NI) driven by a focused XFEL. The maximum NI for 133Ba (unfilled red square), 57Fe (filled blue triangle), 187Os (filled yellow circle), and 169Tm (unfilled greed diamond) is depicted as a function of the photon number per pulse in a (c) platinum- (d) silicon-cladding EWG. Credit: Phys. Rev. Research 4, L032007 (2022)
