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Development of opto-thermal phonon transducer driven by semiconductor laser

半导体激光器驱动光热声子换能器的研制

基本信息

批准号：
11555020
负责人：
SAKAI Keiji
金额：
$ 5.63万
依托单位：
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：
1999
资助国家：
日本
起止时间：
1999 至 2000
项目状态：
已结题

项目摘要

Recently, we developed a new technique to excite high frequency coherent phonon in soft materials using semiconductor lasers. The output of the semiconductor laser is periodically modulated and the laser light illuminates a metal thin film fabricated on the solid substrate. The periodical thermal expansion thus induced in the film excites the mechanical vibration, which emits the coherent ultrasonic wave into the medium contacting with the metal film transducer. In this study, we successfully fabricated a new phonon transducer whose frequency band ranges from 1 MHz up to several hundreds of MHz. The transducer was employed as a phonon source for the ultrasonic spectroscopy measurement. The intensity of the induced phonon by the opto-thermal transducer is about 10,000 times larger than that of the thermal phonon. The sensitivity and the accuracy of the light scattering measurement of the phonon propagation was remarkably improved.We also tried to induce other excitation mode in the medium with lasers, such as the alignment of the molecular orientation. When the laser beam with linear polarization is incident to the liquid sample composed of anisotropic molecules, the molecular orientation is aligned into the direction of the optical polarization due to the Kerr effect. The induced molecular orientation can be sensitively observed with the technique of the optical ellipsometry. We developed a new optical system with the co-axial configuration of the pump and probe lasers. The system enables us to measure quantitatively the optical Kerr constant of various soft materials.The techniques of optical excitation of phonon is now applied to the another experiment of the observation of the Mountain component, which gives the direct information on the ultrasonic relaxation in high frequency range.

最近，我们发展了一种利用半导体激光器在软材料中激发高频相干声子的新技术。半导体激光器的输出被周期性地调制，并且激光照射在固体衬底上制造的金属薄膜。由此在膜中引起的周期性热膨胀激发机械振动，该机械振动将相干超声波发射到与金属膜换能器接触的介质中。在这项研究中，我们成功地制作了一个新的声子换能器，其频带范围从1 MHz到几百MHz。换能器被用作超声光谱测量的声子源。由光热换能器诱导的声子的强度比热声子的强度大约10，000倍。我们还尝试用激光在介质中诱导出其他激发模式，如分子取向的排列。当具有线性偏振的激光束入射到由各向异性分子组成的液体样品时，由于克尔效应，分子取向与光学偏振方向对齐。利用光学椭圆偏振技术可以灵敏地观察到诱导分子取向。我们研制了一种新型的泵浦和探测激光器同轴结构的光学系统。该系统使我们能够定量地测量各种软材料的光学克尔常数，并将光学声子激发技术应用于另一个实验--Mountain分量的观测，给出了高频超声弛豫的直接信息。