BEAMSPLITTER PATH EQUALIZATION FOR WHITE-LIGHT INTERFEROMETRY

In a two-beam, white-light, or polychromatic-light interferometer, any path-length difference in the beamsplitter introduces wavelength-dependent path delay because of the glass dispersion. A technique to align balanced path is described. The method is based on two-or three-wavelength simultaneous interferometry. Difference in intensity of fringes placed symmetrically around the zero interference order (ZIG) is used to measure and equalize the beamsplitter path (BP). As a polychromatic source of light. 660-, 840-, and 780-nm wavelength mixed beams of multimode laser diodes are applied. The technique allows us to balance the path difference with an accuracy better than +/-0.2 mu m. Theoretical background and experimental verification of the method is presented.