Heterodyne white-light interferometer using optical grating

Heterodyne white-light interferometer that uses an optical grating to shift the optical frequency of the white light is proposed. By moving the optical grating, the diffracted lights undergo the frequency shift. The dependency of diffraction angle on wavelength can be resolved by using a spherical mirror, and then heterodyne detection of white-light can be realized with the combination of the optical grating and the spherical mirrors. In practical uses, a tandem-configuration interferometer is useful. The principle was demonstrated and the effect was confirmed experimentally for the first time The surface profile of a step-like object was measured. The signal-to-noise ratio of heterodyne signal is increased by thousand times from that of homodyne signal.