Nulling optical bridge for contactless measurement of changes in reflectivity and/or transmissivity.

摘要

A nulling optical bridge is disclosed herein for the measurement of the difference in the relative power of more than one light beam. The bridge can be used to precisely measure the change in reflectivity and/or transmissivity of a semiconductor device or metal. The bridge operates by splitting at least one illumination source into a number of beams (A; B) wherein one of said beams (B) is made to traverse the sample whose change in transmissivity and reflection characteristics is to be measured. A rotating polarizer (2) is used to equate the intensity of the variable and nonvariable beams under feedback servo control from a photodetector. The incremental quantity of rotation of the polarizer can be calibrated to correspond to a number of characteristics of the sample.