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Novel optical trapping for semiconductor, metal and magnetic particles

用于半导体、金属和磁性颗粒的新型光学捕获

基本信息

批准号：
18360028
负责人：
SATO Shunichi
金额：
$ 8.59万
依托单位：
Tohoku University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
2006
资助国家：
日本
起止时间：
2006 至 2007
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-18360028/
关键词：
optical trapping particles Axially, polarized laser radially polarized laser

项目摘要

The purpose of this study is to achieve a novel optical trapping technique for metal and semiconductor particles by using a radially polarized laser beam, which polarization distributes in a radial pattern. In the first year, stable oscillation of radially or azimuthally polarized beam was achieved by separating polarization components in a laser cavity by a birefringent crystal. As a initial attempt, a c-cut Nd:YVO_4 crystal was selected as a laser material. When this crystal was end-pumped by semiconductor lasers, the output power of approximately 100 m W with radial polarization was obtained. On the basis of this technique, the output power above 2W was observed when a c-cut, non-doped YVO_4 crystal was inserted into a Nd:YAG laser cavity. In the second year, the experiment of optical trapping was performed. A laser beam was focused using a water-immersion objective with the numerical aperture of 1.2. Glass and polystyrene particles were suspended in a glass vessel filled with water and irradiated by the laser focused laser beam. In order to measurer the longitudinal optical trapping force, glass particles were trapped and then the laser power was decreased. The output power, at which the particle was released from the laser trap, was measured and regarded as a critical power. Similar experiments were done for particles with different sizes. The trapping force with a radially polarized laser beam was founded to be lager than that with a linearly polarized beam. This result agrees with the calculation based on the ray optics and shows the validity of the radially polarized laser beam as a trapping beam. The calculation indicated that the radially polarized laser beam is more effective for particles with large refractive index. This implies the validity of the radially polarized beam for the optical trapping of semiconductor particles.

本研究的目的是实现一种新的光学捕获技术的金属和半导体颗粒通过使用径向偏振激光束，其偏振分布在径向图案。在第一年，通过双折射晶体分离激光腔内的偏振分量，实现了径向或方位偏振光束的稳定振荡。作为初步的尝试，选择c切Nd：YVO_4晶体作为激光材料。用半导体激光器端面泵浦该晶体，获得了约100 mW的径向偏振输出。在此基础上，将c切无掺杂YVO_4晶体插入Nd：YAG激光器腔内，获得了2W以上的激光输出。第二年进行了光阱实验。使用数值孔径为1.2的水浸物镜聚焦激光束。将玻璃和聚苯乙烯颗粒悬浮在装有水的玻璃容器中，并通过激光聚焦激光束照射。为了测量纵向光阱力，先捕获玻璃颗粒，然后降低激光功率。测量了粒子从激光阱中释放的输出功率，并将其视为临界功率。对不同尺寸的颗粒进行了类似的实验。发现径向偏振激光束的捕获力大于线偏振激光束的捕获力。这一结果与基于射线光学的计算结果一致，表明了径向偏振激光束作为俘获光束的有效性。计算表明，径向偏振的激光束对折射率大的粒子更有效。这意味着径向偏振光束对半导体粒子的光学捕获的有效性。