Optical measuring device for detecting surface characteristics of object

An optical measuring device comprising:

• a laser ray source for emitting a laser ray, an objective lens for condensing the ray from said laser ray source as an incident ray on a surface of a substance to be measured, a polarization element for passing the ray from the laser ray source to the objective lens and for guiding a reflected ray which is reflected from the surface of the substance and through the objective lens to a direction other than said ray source, a ray dividing element for dividing the reflected ray from the polarization element into two identical divided rays which are transmitted in two directions along two optical axes, two prisms each receiving one of the divided rays and each having a reflecting surface forming substantially the critical angle relative to each optical axis of the reflected ray, and two divided photo detecting elements each operative to detect the ray quantity change of the reflected ray reflected from its corresponding prism, the two divided photo detecting elements having a pair of divided light-receiving surfaces 33A and 33B and a pair of divided light-receiving surfaces 34A and 34B, respectively, for receiving thereon the reflected rays to produce outputs I.sub.33 A, I.sub.33 B, I.sub.34 A and I.sub.34 B corresponding to the ray quantities of the reflected rays received by the light-receiving surfaces 33A, 33B, 34A and 34B, respectively, so that the surface of the substance to be measured is detected on the basis of a difference between the sum of I.sub.33 B and I.sub.34 A and the sum of I.sub.33 A and I.sub.34 B.