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Development of phase-coherent light scattering method using mode-selective light excitation

利用模式选择性光激发开发相位相干光散射方法

基本信息

批准号：
12555009
负责人：
TANAKA Hajime
金额：
$ 8.51万
依托单位：
The University of Tokyo
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
2000
资助国家：
日本
起止时间：
2000 至 2002
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-12555009/
关键词：
Phase-coherent light scattering method light grating mode selective excitation Dynamics of fluctuation liquid crystal isotropic phase complex spectrum Critical phenomena of specific heat frequency-tunable CW laser モード選択熱拡散モードRayleighスペク

项目摘要

We developed a new method of dynamic light scattering, which enables us to make 'mode-selective' measurement of Rayleigh-Brillouin scattering in liquids. Different from the conventional light scattering methods, which measure the power spectrum of light scattered by spontaneously excited fluctuations, we generate a coherent grating by using a laser-induced scanning interference pattern and measure complex spectra of a light-excited mode by its phase-sensitive superheterodyne detection. The mode-selectivity of our phase-coherent light scattering method is a unique feature, which cannot be realized by the conventional light scattering methods measuring the power spectrum of light scattered by spontaneously excited fluctuations. This is particularly useful to study the mode usually hidden behind large fluctuations of another mode. For example, we can control the amplitude of the temperature grating by changing the absorption coefficient of a liquid by adding a small amount of dye molecules. This controllability of the signal intensity and the resulting mode selectivity allow us to pick up only a thermal diffusion mode even under the existence of other incoherent modes with large amplitude. To demonstrate the capability of our method, we study a thermal diffusion of liquid crystals in isotropic phase ; in conventional methods in frequency domain, the spectra of thermal diffusion mode are usually hidden behind ones of orientational relaxation mode near its phase-transition point. Using our method, we found sudden decreases in both spectral amplitudes and linewidths near a transition point, which we regard as the reflection of the singular behavior of the specific heat and the thermal diffusivity, respectively. This is the first measurement of the thermal singularity near the phase-transition point of liquid crystalline sample in isotropic phase by using dynamic light scattering methods.

提出了一种新的动态光散射方法，使我们能够对液体中的瑞利-布里渊散射进行“模式选择”测量。与传统的光散射法测量自发激发涨落散射光的功率谱不同，我们利用激光感生扫描干涉图样产生相干光栅，并利用其相敏超外差探测法测量光激发模的复谱。我们的相位相干光散射方法的模式选择性是一个独特的功能，这是不能实现的传统的光散射方法测量自发激发的波动散射光的功率谱。这对于研究通常隐藏在另一种模式的大幅波动背后的模式特别有用。例如，我们可以通过添加少量染料分子来改变液体的吸收系数，从而控制温度光栅的振幅。这种信号强度的可控性和由此产生的模式选择性，使我们能够拿起只有一个热扩散模式，即使在存在其他非相干模式与大幅度。为了证明我们的方法的能力，我们研究了液晶在各向同性相的热扩散，在频域的常规方法，热扩散模式的频谱通常隐藏在其相变点附近的取向弛豫模式的频谱之后。使用我们的方法，我们发现突然下降的光谱振幅和线宽附近的过渡点，我们认为作为反射的奇异行为的比热和热扩散率，分别。这是首次用动态光散射方法测量液晶各向同性相相变点附近的热奇异性。