MICHELSON'S INTERFEROMETER

PURPOSE:To accurately measure minute displacement by preventing the fluctuation of an interference fringe formed by correcting the length of the light path of reflected light due to a mirror so as to negate the output deviation of two photodiodes receiving interference light. CONSTITUTION:The light from a light source 2 is split into two lights by a half mirror 1 while both lights are reflected by the first mirror 3 of an article 7 to be measured and the second mirror 4 of a piezoelectric actuator 4 and both reflected lights interfere to be received by two photodiodes, which are provided at an interval half the wavelength of the luminous intensity curve of the interference fringe on a light receiving surface 6, through a lens 5. When the outputs of both photodiodes are supplied, an actuator is controlled through a control circuit 8 and the length of the light path of the reflected light by the mirror 4 is adjusted so as to negate the output deviation of both photosiodes. As a result, the generation of the fluctuation of the interference fringe is prevented and the minute vibration displacement of the article 7 to be measured is accurately measured.