SURFACE SHAPE MEASURING DEVICE

PURPOSE:To measure the shape of a surface with high accuracy and with stable quality, when the surface shape of an unknown subject is to be obtained, by carrying out such a corrective treatment that the shape offset previously stored is substracted from the measured shape. CONSTITUTION:The monochromatic coherent light beams emitted from a laser beam source 1 are splitted into two parts by a beam splitter 5, and the one part of the splitted beams are returned to the incident direction by a reflecting mirror 7 as a reference light, and are introduced into a collimator lens 3e. Another part of the beams are enlarged by collimator lenses 3c, 3d as body light so as to have a required beam diameter, and thereafter, are introduced into the lens 3e by the beam splitter 5 in the same way as the reference light, so that they are superposed on the reference light. The reference light and the body light are subjected to photoelectric conversion by a two-dimensional photodetector 11 in their interference intensities in the detecting surface, and the phase information of the body light can be obtained from the interference intensities by means of a signal processor 12, so that the shape of the surface can be obtained. In this case, a measured shape corrective means 13 is added between the signal processor and an output device 14 for carrying out corrective treatment.