Interferometer for measuring ultrasmall displacements with a nonmonochromatic light source

A dispersionless multiple-beam interferometer with a small distance between mirrors is described. The phase characteristics of the mirrors are chosen in such a way that the resonance condition depends only weakly on the frequency of the light, while a high sensitivity to displacement of the mirrors is retained. It thus becomes possible to significantly relax the requirements on the spectral width and frequency stability of the laser light source.