Department of Physical Science, Graduate School of Science, Osaka Prefecture University, 1-1 Gakuen-cho, Naka-ku, Sakai 599-8531, Japan.
Phys Rev Lett. 2013 Feb 15;110(7):077402. doi: 10.1103/PhysRevLett.110.077402. Epub 2013 Feb 13.
The detection-energy dependence of a coherent phonon in a (001) CdTe crystal, generated by ultrashort laser pulses with the center energy transparent or opaque to the sample, is investigated using a spectrally resolved pump-probe method. At the excitation in the transparent region, the detection-energy dependence of the phonon amplitude has two peaks at the energy shifted by one times the phonon energy of CdTe from the center energy of the probe pulses. On the other hand, the amplitude in the opaque region shows two peaks at the energy shifted by about two times the phonon energy. This difference occurs even though the observed energies of the coherent phonons in both regions are the same as that of the longitudinal optical phonon of CdTe. The energy shifts in the detection-energy dependence imply that the emission and absorption of one phonon and two phonons in the transparent and opaque regions, respectively, are implicated in coherent phonon generation. In this study, the detection-energy dependence is examined from the viewpoint of the third-order nonlinear susceptibility based on the impulsive stimulated Raman scattering process under nonresonant and resonant conditions.
利用光谱分辨的泵浦-探测方法研究了在（001）CdTe 晶体中由中心能量对样品透明或不透明的超短激光脉冲产生的相干声子的探测能量依赖性。在透明区域激发时，声子幅度的探测能量依赖性在偏离探测脉冲中心能量一个声子能量的位置出现两个峰。另一方面，在不透明区域的幅度在偏离约两个声子能量的位置出现两个峰。即使在两个区域中观察到的相干声子的能量与 CdTe 的纵光学声子的能量相同，也会出现这种差异。探测能量依赖性中的能量位移意味着透明和不透明区域中的一个声子和两个声子的发射和吸收分别涉及相干声子的产生。在这项研究中，从非共振和共振条件下基于脉冲受激拉曼散射过程的三阶非线性极化率的角度检查了探测能量依赖性。
