Science. 1987 Sep 4;237(4819):1147-54. doi: 10.1126/science.237.4819.1147.
Interfering light waves produce an optical interference pattern in any medium that interacts with light. This modulation of some physical parameter of the system acts as a classical holographic grating for optical radiation. When such a grating is produced through interaction of pulsed light waves with an optical transition, a transient grating is formed whose decay is a measure of the relaxation time of the excited state. Transient gratings can be formed in real space or in frequency space depending on the time ordering of the interfering light waves. The two gratings are related by a space-time transformation and contain complementary information on the optical dynamics of a system. The status of a grating can be probed by a delayed third pulse, which diffracts off this grating in a direction determined by the wave vector difference of the interfering light beams. This generalized concept of a transient grating can be used to interpret many picosecond-pulse optical experiments on condensed-phase systems. Examples of some low-temperature experiments will be presented. In principle, many of these experiments could also be performed by using stochastic broad-band excitation. In these nonlinear photon-interference experiments the time resolution is determined by the correlation time of the light source rather than its pulse width.
干涉波在任何与光相互作用的介质中产生光学干涉图案。系统的某些物理参数的调制充当光辐射的经典全息光栅。当通过脉冲波与光学跃迁的相互作用产生这样的光栅时，形成的瞬态光栅的衰减是测量激发态弛豫时间的量度。瞬态光栅可以根据干涉光的时间顺序在实空间或频率空间中形成。这两个光栅通过时空变换相关联，并且包含关于系统的光动力学的互补信息。通过延迟的第三脉冲可以探测光栅的状态，该第三脉冲在由干涉光束的波矢量差确定的方向上衍射出该光栅。这种瞬态光栅的广义概念可用于解释凝聚相系统的许多皮秒脉冲光学实验。将呈现一些低温实验的例子。原则上，也可以通过使用随机宽带激励来执行许多这些实验。在这些非线性光子干涉实验中，时间分辨率由光源的相关时间而不是其脉冲宽度确定。
