Brillouin Scattering Study on Thermal Phonon Resonance

在以往的研究中，我们已经成功地将光学加热光谱技术引入到布里渊散射实验中。该技术为研究软质材料中各种分子动力学现象提供了一种非常有效的手段，包括(a)首次观察到布里渊三重态的真实形状，(b)高各向异性分子中去偏振光散射的异常光谱形状。(c)非平衡材料中布里渊峰的Stokes和反Stokes分量之间的不对称性。本研究的目的是将新技术应用于热声子共振，即自然声子在有限空间内显示共振效应的奇怪现象。我们试图描述这种现象的物理机制，并找到它的应用，例如，布里渊散射在液体中表现出分子水平的特征结构，在边界附近或在非常少量的样品中。在本研究中，我们建立了“热声子共振布里渊散射”方法，使我们能够以0.1%的精度测量100 μ m大小的小体积内激发的声子。在边界附近的光散射实验中，最严重的问题是杂散光，杂散光必须比微弱的信号光强。为了避免这种有害影响，我们开发了一种偏振调制锁定检测技术，该技术可以清晰地观察到低角散射（rheta-1）的光谱，并且具有足够的精度。本研究建立的新方法正被应用于软质材料的动力学研究，并产生了几个有趣的结果。该方法突破了已有30多年历史的布里渊散射。

In our previous studies, we had already succeeded in introducing the optical beating spectroscopy technique to Brillouin scattering experiment. The resolution 100 to 1000 times higher than the previous experiments was realized The technique provided us with a very effective means to investigate various phenomena of molecular dynamics in soft materials including (a) the first observation of the true shape of Brillouin triplet, (b) anomalous spectrum shape of depolarized light scattering in highly anisotropic moleculeds, and (c) the observation of asymmetry between the Stokes and the anti-Stokes components of Brillouin peaks in materials out of equilibrium.The purpose of the present study was to apply the new technique for the thermal-phonon resonance, the strange phenomenon that the natural phonons confined in a limited space reveal resonance effect. We intended to describe the physical mechanism of the phenomenon and find its applications, for instance, Brillouin scattering in liquids which show characteristic structures at molecular level near boundary or in specimen of very small amount.In the present study we established the method, "Brillouin scattering of thermal-phonon resonance" which enabled us to measure the phonons excited in a small volume-100mu m in size with 0.1% precision. The most serious problem in the light scattering experiment near boundaries would be the stray light which is must stronger than the weak signal light. To avoid this harmful effect, we developed a technique of polarization modulation for lock-in detection by which the spectrum of low-angle scattering(rheta-1ﾟ)was clearly observed with sufficient accuracy.The new method established in this study is being applied for studying dynamics of soft materials, yielding several interesting results. The method made a breakthrough to the Brillouin scattering which has more than 30 years history.