SIMULTANEOUS MEASURING SYSTEM FOR SPEED, DIAMETER AND REFRACTIVE INDEX OF PARTICLE BY MULTIPLE FOCAL POINT METHOD USING LASER

摘要

PURPOSE:To make it possible to measure the speed, diameter and refractive index of a particle simply and accurately by using multiple interferences of a diffraction grating, and forming sharp interference fringes. CONSTITUTION:The diameter of a laser beam is expanded through lenses l1 and l2. The laser beam is diffracted through a diffraction grating d.g. and made to be parallel light beams through a lens l3. Thereafter, sharp interference fringes (multiple focal points) which are condensed on a focal plane at the rear side of the lens l3 are used for measurement. As the diffraction grating d.g., a pulse-width modulated phase diffraction grating is used. Apertures a1 and a2 are used for selecting only a time when a particle passes the central orbit of multiple focal point. The reflected light and the refracted light are received with detectors PD1 and PD2. The speed of the particle can be obtained from the period of a signal which is obtained from the reflected light that is generated when the particle passes the multiple focal points. The reflected light is detected with the detector PD2, and then the refracted light is detected with the detector PD1. Furthermore, the refracted light is observed with the PD2, and the reflected light is observed with the PD1. Therefore, the diameter and the refractive index of the particle are obtained based on the time delay of the signals obtained with the PD1 and the PD2.