Theory of degenerate four-wave mixing in resonant Doppler-broadened media. - II. Doppler-free heterodyne spectroscopy via collinear four-wave mixing in two- and three-level systems
Theory of degenerate four-wave mixing in resonant Doppler-broadened media. - II. Doppler-free heterodyne spectroscopy via collinear four-wave mixing in two- and three-level systems
复制标题
谐振多普勒展宽介质中简并四波混频理论。
DOI：
10.1051/jphys:0198200430105700
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发表时间：
1982
期刊：
影响因子：
--
通讯作者：
D. Bloch
中科院分区：
文献类型：
--
作者：
M. Ducloy;D. Bloch
在本文中，我们分析了一种新的灵敏光谱技术，其中样品池受到双频泵浦光束 (ω + Δ ± δ/2) 和反向传播探测光束 (ω) 的照射。通过四波混频过程以频率 ω ± δ 重新发射的相位共轭场通过其与探测场的外差跳动来检测。外差拍频信号的特性通过介质非线性响应的微扰计算来研究，在入射场中进行三阶。在谐振气体介质中，发射线形表现出无多普勒双峰结构[单光子谐振频率分裂 3 δ/2，双光子跃迁频率分裂 δ/2]。通过使用差频信号的相敏检测，可以单独分析非线性磁化率的实部（色散）或虚部（吸收）。对于单光子跃迁，信号相移与原子能级寿命相关，并允许人们研究气相中的弛豫动力学（如猝灭碰撞、速度扩散等）。这对于交叉共振特别有趣，其中只有公共电平起作用。在三能级系统中，人们还预测通过拉曼型双光子过程会选择性共振增强相位共轭发射。这些预测大部分都已得到实验验证。
In this article, we analyse a new sensitive spectroscopic technique in which a sample cell is irradiated by a two-frequency pump beam (ω + Δ ± δ/2) and a counter-propagating probe beam (ω). The phase-conjugate fields re-emitted at frequencies ω ± δ, via four-wave mixing processes, are detected through their heterodyne beating with the probe field. The properties of the heterodyne beat signal are studied by means of a perturbation calculation of the nonlinear response of the medium, carried out to the third order in the incident fields. In resonant gas media, the emission lineshape exhibits a Doppler-free doublet structure [frequency splitting 3 δ/2 for single-photon resonances, and δ/2 for two-photon transitions]. By using a phase-sensitive detection of the beat signal, one can separately analyse real (dispersion) or imaginary parts (absorption) of the nonlinear susceptibility. For single-photon transitions, the signal phase shift is related to the atomic levels lifetime and allows one to study the relaxation dynamics in gas phase (like quenching collisions, velocity diffusion, etc...). This is particularly interesting for cross-over resonances, in which only the common level contributes. In three-level systems, one also predicts a selective resonant enhancement of the phase-conjugate emission through Raman-type two-photon processes. Most of these predictions have been experimentally verified.