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Study of hydrogen-mode dynamics and phase transition mechanism by coherent phonon excitation

相干声子激发研究氢模动力学和相变机制

基本信息

批准号：
06402009
负责人：
YAGI Toshirou
金额：
$ 20.93万
依托单位：
HOKKAIDO UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (A)
财政年份：
1994
资助国家：
日本
起止时间：
1994 至 1996
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-06402009/
关键词：
PHASE TRANSITION ISBS STIMULATED LIGHT SCATTERING SELECTIVE EXCITATION PHONON EXCITATION SOFT MODE POLARIZATION FLUCTUATION 誘電光散乱

项目摘要

In the first year, 1994, of this project, we concentrated our effort to construct newly the experimental system for coherent phonon excitation. The light source of the excitation pulse was a mode-locked Q-switched YLF laser. Two coherent light pulses, produced from one pulse by a half-mirror, with a time-width of 60 picosecond were coincided each other temporally and also spatially in a small area selected in the specimen The temporal interference pattern produces an electronic field strong enough to excite a phonon mode which begins to propagate in two opposite directions with a definite wave vector after the excite pulses passed through the excitation area. The excited phonons are probed in real time as a change of the intensity of the light diffracted from the phonons. In this stage of the study, a cw argon laser was employed as a light source of the probe light. In the second stage of the present project (1995-1996), we improved the system by introducing a pulse-probe method. The new version of the experimental system gave us an excellent signal to noise ratio of the light diffracted from the excited phonons. In the final period, 1996-1997, we applied our system to investigate the phase transition dynamics in several cases ; typical uniaxial ferroelectrics tri-glycine sulphate and selenate, a hydrogen-bonded ferroelectric rubidium hydrosulfate, a hydrogen-bonded ferroelastic potassium trihydrogen selenate, an orientational order-disorder ammonium chloride and water as a typical hydrogen system. Ineach case, we succeeded to excite a coherent phonon as an excellent probe to observe the dynamical aspect of the order parameter coupled with phonons. Exact values of the characteristic relaxation time were given for each of these cases in addition to a new phenomenon observed at just above the freezing point of the supercooled water.

1994年，我们集中力量重新建立了相干声子激发的实验系统。激发脉冲的光源是锁模调Q YLF激光器。用半透半反镜从一个脉冲中产生两个时宽为60皮秒的相干光脉冲，在样品中选定的一个小区域内，在时间和空间上相互重合。时间干涉图样产生一个足够强的电场，激发出一个声子模，该声子模在激发脉冲通过激发区后开始以确定的波矢向两个相反的方向传播。激发的声子在真实的时间中被探测为从声子衍射的光的强度的变化。在此阶段的研究中，采用连续氩激光器作为探测光的光源。在本项目的第二阶段（1995-1996年），我们通过引入脉冲探测法改进了系统。新版本的实验系统给了我们一个很好的信号噪声比的光从激发声子衍射。在最后一个时期，1996-1997年，我们应用我们的系统来研究在几种情况下的相变动力学;典型的单轴铁电三甘氨酸硫酸盐和硒酸盐，氢键铁电硫酸氢铷，氢键铁弹钾三氢硒酸盐，取向有序无序氯化铵和水作为一个典型的氢系统。在每种情况下，我们都成功地激发了一个相干声子，作为观察与声子耦合的序参量的动力学方面的一个很好的探针。给出了这些情况下的特征弛豫时间的精确值，此外还观察到一个新的现象，在刚刚超过过冷水的凝固点。