Patent ID: 7876449

Claim:
A laser interferometer, comprising: a laser source for emitting a laser beam, a reference surface provided at a predetermined position for reflecting the laser beam; and a measurement surface provided on a target object for reflecting the laser beam, the laser interferometer measuring a displacement of the target object by calculating a displacement of the measurement surface based on an interference light reflected by the reference surface and the measurement surface, wherein the laser source emits the laser beam while stabilizing a center wavelength of the laser beam by modulating the laser beam using a modulation signal of a predetermined frequency, the laser interferometer further comprising: a sampling unit that acquires a sampling value by sampling the interference light in accordance with a sampling frequency that is a multiple of an integer of two or more of a frequency of the modulation signal; and an average calculator that calculates an average value by averaging the sampling value in time-series acquired by the sampling unit in accordance with the sampling frequency, a displacement of the measurement surface being measured based on the average value calculated by the average calculator.