Focussing error detection using Michelson interferometer - evaluating periodic frequency or phase of interference pattern formed at detector by two reflected sub-beams

摘要

Light transmitted in two parallel sub beams (6,7) parallel to and at equal distances from the optical axis is focused towards the object (10) by an objective lens (8). The reflected light from both sub-beams is superimposed and detected. The position error or the variation in the position error is determined from the periodic frequency of the interference pattern which is formed at the detector or detectors (15,16,19,20) or from the derivative of the phase values of the interference pattern. USE/ADVANTAGE - For detecting deviations of object from focal point of objective lens, e.g. for use in mfg. to determine positions and measure distances. Resolutions of less than 1 micron can be achieved for unambiguity ranges of over 100 microns.