A new phase-shifting scatterplate interferometer is realized by exploiting the polarization characteristics of a birefringent scatterplate. Controlling the component of polarization that is scattered allows the birefringent scatterplate to separate the test and reference beams. The advantages of this design are that it does not require auxiliary optics to be placed near the surface under test and the "hot spot" and background irradiance, which are inherent to scatterplate interferometers, can be eliminated. This study provides a description of the phase-shifting birefringent scatterplate interferometer, expands the theoretical model of the scatterplate interferometer to include polarization and phase shifting, analyzes the performance of the new interferometer and discusses possible sources of error induced by the design. In addition, a few component specific topics are addressed. Two methods for generating the birefringent scatterplate are presented and the role the scatterplate plays in removing the "hot spot" is explored. Furthermore, the practicality of using a liquid crystal retarder for phase shifting is analyzed in the process of determining the performance of the interferometer.
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