TRAPPING AND SENSING OF A SINGLE PARTICLE WITH A DIODE LASER

提出了一种利用半导体激光器的激光捕获和自混合干涉测量液体中微米级颗粒的技术。通过激光捕获，可以固定和操纵液体中的单个粒子。这个想法是利用粒子的后向散射激光同时测量被捕获粒子的位移。利用光对原激光腔的反馈效应，可以灵敏地获得粒子在纳米量级的位移，并发展了一种利用外调制测量粒子-激光系统弹性常数的方法。弹簧常数的测量精度较高，可用于识别液体中的颗粒，如血细胞、病毒等。利用半导体激光器的反馈效应，通过数字FFT方法和模拟锁相放大器，实现了位移的精确测量。位移的测量精度可达10 nm左右，并提出了利用参考反射镜进一步改进的方法，还利用半导体激光器的反馈效应测量了血流量。采用脉冲计数法和相关分析法对血液随机反馈效应产生的激光散斑信号进行了分析。

This research proposed a technique of measuring micron size particle in liquid with laser trapping and self-mixing interferometer using a laser diode. By laser trapping it is possible to fix and manipulate a single particle in liquid. The idea is to measure the displacement of the trapped particle simultaneously using the backscattered laser light from the particle. The feedback effect of the light to the original laser cavity provides a sensitive mean to get the displacement of the particle in nanometer order.In the research we have also developed a method to measure the spring constant of the particle-laser system by using external modulation. The better precision of measuring the spring constant can be used to recognize particles in liquid, such as blood cells, viruses. We also developed a technique to determine exactly the displacement using the feedback effect of laser diode by digital FFT method and an analog lock-in amplifier. The displacement can be measured in a precision of about 10 nanometers, and further improvement of the measurement has be proposed using a reference reflector.The feedback effect of a laser diode is also applied to measure the blood flow. The pulse counting method and correlation method has been developed to analyze the speckle signal of the laser output due to the random feedback effect of the blood.