Interference effects in compound and achromatic wave plates

Compound and achromatic wave plates are investigated with respect to multiple-beam interference within their elements. The phase delay, transmittance and polarizance are all shown to display fringes through the spectrum. In the past, achromatic devices have had apparent success in instruments with spectral pass-bands which are sufficiently broad to average out the effects of the fringe structures. According to the accuracy of any prospective measurement, it is now shown that their intended properties require detailed scrutiny when they are employed in optical systems involving medium to high spectral resolution.