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Excitation of Soft Acoustic Mode by Stimulated Brillouim Scattering and Phase Transition Dynamics

受激布里渊散射和相变动力学的软声模激发

基本信息

批准号：
05452034
负责人：
KINOSHITA Shuichi
金额：
$ 2.94万
依托单位：
Osaka University
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (B)
财政年份：
1993
资助国家：
日本
起止时间：
1993 至 1994
项目状态：
已结题

项目摘要

the purpose of this research is to excite phonon in material directly by impulsive stimulated Brillouin scattering and to clarify the role of the phonon in phase transition phenomena. In the present work, we have done the following exeriment : 1) Measurement of quasi-longitudinal acoustic mode in TGSe (triglycine selenate) near the ferroelectric phase transition, 2) Development of femtosecond stimulated light scattering system, 3) Direct comparison of femtosecond optical Kerr effect spectroscopy with high resolution light scattering spectrum, 4) Experimental verification of the breakdown of Debye model.1) TGSe is a crystal which undergoes ferroelectric phase transition at 22? A1C.Below the transition point, the anomaly in the velocity of the quasi-longitudinal phonon mode C_<33> has been found from the light scattering and ultrasonic experiments. This anomaly comes from the coupling of the phonon modes with the polarization fluctuation. Since the characteristic frequency of the polariz … More ation fluctuation is temperature-dependent, the velocity anomaly occurs at different temperatures dependent on the frequency of the phonon measured. In the present work, we have measured the temperature dependence of the phonon velocity in the intermediate frequency region (450 MHz) and have confirmed the proposed mechanism of this anomaly experimentally.2) We have developed the femtosecond version of the stimulated light scattering. This system provides the excitation of THz phonon.3) Optical Kerr effect spectroscopy and spontaneous light scattering in off-resonance excitation region are connected through fluctuation-dissipation theorem and we have confirmed this theorem experimentally by use of the high-resolution ligh scattering and femtosecond optical Kerr effect measurements.4) Debye model has been often used to express the fluctuational behavior in phase transition studies. However, this model accompanies essential difficulty in itself such as breakdown of the momentum sum rule. Since the breakdown of this model is clearly observed in the time-domain by the finite initial rise in the response function, we have performed the experiment using typical liquids as samples. The response function obtained by the femtosecond optical Kerr effect and femtosecond polarization-selective four wave mixing experiment shows a clear initial rise in every sample. It is suggested that the breakdown of Debye model has serious effect when the fluctuation in a wide frequency range is discussed such as in glass transtions. Less

本研究的目的是通过脉冲受激布里渊散射直接激发材料中的声子，并阐明声子在相变现象中的作用。在本工作中，我们做了以下工作：1)测量了TGSe(甘氨酸硒酸盐)铁电相变附近的准纵声模，2)发展了飞秒受激光散射系统，3)直接比较了飞秒光学克尔效应光谱和高分辨率光散射光谱，4)实验验证了德拜模型的击穿。1)TGSe晶体在22？在过渡点以下，从光散射和超声实验中发现准纵向声子模C_&lt；33&gt；的速度反常。这种反常现象来自于声子模与偏振涨落的耦合。由于极化…的特征频率更多的离子涨落是温度相关的，速度异常发生在不同的温度取决于被测声子的频率。在本工作中，我们测量了中频区(450 MHz)声子速度与温度的关系，并从实验上证实了这种反常现象的机制。2)我们发展了飞秒版本的受激光散射。该系统提供了太赫兹声子的激发。3)光学克尔效应光谱和非共振激发区的自发光散射通过涨落耗散定理联系在一起，我们利用高分辨率的光散射和飞秒光学克尔效应测量在实验上证实了这一定理。4)在相变研究中，通常使用德拜模型来描述涨落行为。然而，这个模型本身就伴随着基本的困难，例如动量和规则的崩溃。由于通过响应函数的有限初始上升在时间域中可以清楚地观察到该模型的击穿，因此我们以典型液体为样本进行了实验。由飞秒光学克尔效应和飞秒偏振选择四波混频实验得到的响应函数在每个样品中都有明显的初始上升。结果表明，当讨论较宽频率范围内的涨落时，如在玻璃跃迁中，德拜模型的击穿将产生严重影响。较少