相干布居俘获中的Dicke窄化理论
Theory of Dicke narrowing in coherent population trapping
摘要：
多普勒效应是热蒸气光谱中主要的展宽机制之一。对于双光子跃迁，人们会天真地认为多普勒效应会导致与波矢差成比例的残余展宽。在相干布居俘获（CPT）中，这是一种窄带现象，实验上没有观察到这种展宽。这通常归因于频繁的速度变化碰撞，已知窄多普勒加宽的单光子吸收线（迪克窄化）。在这里，我们从理论上表明，这样的窄化机制确实存在CPT共振。窄化因子是原子的平均自由程和与两个辐射场的波矢差相关联的波长之间的比率。提出了一个可能的实验来验证这一理论。
英文摘要：
The Doppler effect is one of the dominant broadening mechanisms in thermal vapor spectroscopy. For two-photon transitions one would naively expect the Doppler effect to cause a residual broadening, proportional to the wave-vector difference. In coherent population trapping (CPT), which is a narrow-band phenomenon, such broadening was not observed experimentally. This has been commonly attributed to frequent velocity-changing collisions, known to narrow Doppler-broadened one-photon absorption lines (Dicke narrowing). Here we show theoretically that such a narrowing mechanism indeed exists for CPT resonances. The narrowing factor is the ratio between the atom's mean free path and the wavelength associated with the wave-vector difference of the two radiation fields. A possible experiment to verify the theory is suggested.
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