Optical apparatus for the detection of scattered light

摘要

An optical apparatus for the detection of scattered light has a light source for supplying a beam of light with a determined wavelength, an objective lens for focusing the light beam on a test object and a photo receptor for receiving the light scattered around the objective lens by the boundaries of a pattern on the test object. The apparatus further has a light converging ring member and a filter arranged in the optical path between the test object and the photo receptor to allow the scattered light from the test object to enter the filter and the photo receptor after the scattered light is converted into a beam of substantially collimated rays by the action of reflection and convergence by the converging ring member.