Automatic fringe recognition and detection of subwavelength phase perturbations with a Michelson interferometer

Simple systems and procedures based on personal computer hardware to analyze the fringe pattern in a Michelson interferometer, retrieve information on the irregularities of the combined phase front and use it to obtain a correct interferogram are presented. In one system, where one of the mirrors can be moved piezoelectrically, good sensitivity (lambda/30) is obtained while using an economical array of 1-bit image sensing elements. In another system, based on a TV camera and a 6-bit frame grabber, images of the two separate laser beams and of the fringe patterns are stored; by adequate numerical analysis, higher sensitivity (lambda/100) is achieved.