Hyper-resolution Brillouin-rayleigh Spectroscopy by Optical Beating Technique

自从20世纪60年代中期，Fleury和焦立中首次成功地观测到布里渊三重态以来，由扫描法布里-珀罗涉仪和高灵敏度光电倍增器组成的光散射系统一直是所有布里渊散射实验的通用标准。人们一直在努力提高实验的分辨率，但通常认为这并不令人满意。例如，已经开发了一种非常复杂的系统，其中计算机串联控制多路法布里-珀罗标准具或多路法布里-珀罗标准具。为了减少由光源的光谱宽度引入的附加线展宽，使用了带有稳频装置的单纵模激光器，由此产生的输出功率的不足通过冷却的光电倍增管和随后的光子计数器的检测灵敏度的提高来补偿。因此，今天的布里渊散射系统通过…变得越来越复杂更重要的是，它的基本部分仍然停留在弗洛里和焦立中的实验中。另一方面，人们提出了一种基于完全不同原理的布里渊散射实验的想法，即用光谱分析仪取代法布里-珀罗标准具的光拍光谱技术。沿着这条线进行了各种实验，但大多数都没有成功，只有一个例外。最近，我们成功地研制出了一种新的超分辨率布里渊散射系统，其频率分辨率提高了10^3-104倍。在本研究中，我们进一步改进了光散射系统，用它进行了一些复杂的实验，包括(1)观察到聚合物固体中的声子弛豫现象，(2)发现了热声子共振，(3)研究了在非平衡态下观察到的布里渊三重态的非对称性。较少

The light scattering system with a scanning Fabry-Perot interferometer and a high-sensitivity photo-multiplier has long been the general standard of all the Brillouin scattering experiments ever since Fleury and Chiao first succeeded in the observation of a Brillouin triplet in the middle of the 1960's. Every endeavor has been made to improve the resolution of the experiment, which has not generally been considered satisfactory. A very sophisticated system in which a computer controls multipass Fabry-Perot etalon or etalons in tandem, for example, has been developed. To reduce the additional line broadening introduced by the spectrum width of the light source, a single longitudinal mode laser with a frequency-stabilizing device has been utilized, the resultant lack of output power being compensated by the increased detection sensitivity of a cooled photo-multiplier tube followed by a photon counter. The Brillouin scattering system of today is thus becoming more and more complicated tho … More ugh its essential part still stays within the experiment of Fleury and Chiao. Nevertheless, all these efforts to achieve higher resolution seems to have been rewarded with rather limited success.On the other hand, the idea of a Brillouin scattering experiment base on a completely different principle has been proposed, i.e., the technique of light beating spectroscopy in which the Fabry-Perot etalon is replaced with a spectrum analyzer. Various experiments have been tried along this line, but most of them were unsuccessful with only one exception. Recently we succeeded in the development of a new system of hyper-resolution Brillouin scattering in which the frequency resolution was increased by 10^3-10^4 times. In this study, we further improved the light scattering system with which we conducted some sophisticated experiments, including (1) observation of phonon relaxation phenomenon in polymer solids, (2) discovery of thermal phonon resonance and (3) investigation of asymmetry in Brillouin triplet observed under non-equilibrium state. Less