This paper shows how a single <i>Z</i>-cut plate of a uniaxial crystal can be used as a two-beam interferometer or Fourier-transform spectrometer. As a visual device, it permits easy identification of a set of achromatic fringes that can be seen in any two-beam interferometer when a white-light source is observed through it. These fringes apparently have not been described previously. They are expected when we understand that the white-light fringe pattern is in fact the Fourier transform of the spectral-sensitivity curve of the eye.
Bruce H. Billings, "Visual Fourier-transform spectroscopy with a single crystal plate," J. Opt. Soc. Am. 65, 817-824 (1975)