Laser scanning microscope with a differential heterodyne optical probe

A new laser scanning microscope system has been developed to observe the spatial distribution of light scattering particles or defects in a partially transparent object. The present microscope has an optical probe whose intensity is modulated by the interference effect between two crossed laser beams with slightly different frequencies. In this paper, a Zeeman laser combined with a simple polarizing optical system is used to produce two such coherent beams. Experimental results obtained by using a latex sphere and a microscale as the target show qualitatively that high image contrast is obtained by the present method even if some obscuring particles exist in front of the probe volume. Distributions of light scattering particles or defects in a LiNbO₃ and TGS single crystal can be visualized by a computer-controlled scan stage.