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Measurement of the residual wedge angle of a nontransparent parallel plate with a modified cyclic path optical configuration.

A new technique for the measurement of the residual wedge angle (RWA) of a nontransparent nearly parallel plate (NPP), using a polarized He-Ne laser source, is proposed. A modified cyclic path optical configuration is used to produce counterpropagating collimated beams, which get reflected from the end surfaces of the NPP and are combined to produce two-beam Fizeau fringes, whose spacing is inversely proportional to the wedge angle of the NPP. The states of polarization of the beams reflected from the end surfaces of the NPP are transformed to opposite circular polarizations, and polarization phase shifts are applied between them. Phase shifting interferometry (PSI) has been used to determine the angular tilt between the interfering beams and, hence, the RWA of the NPP. Results obtained from a validation experiment are presented. The PSI-based technique does not suffer from any measurement ambiguities due to limitations in effective beam aperture.