Cube beam-splitter interferometer for phase shifting interferometry

A cube beam splitter (CBS), which is more often used in two beam interferometers to generate orthogonally directed light beams, can interestingly be used to construct a two beam interferometer by aligning its beam splitting surface parallel to the direction of propagation of light. It is shown that in such a configuration, an optical sample placed so as to intercept one half of the expanded incident beam may be tested for phase or surface distortions. The proposed set-up can be used as well to construct a phase shifting interferometer by properly incorporating a quarter-wave plate and a polarizer for phase shifting, which can then be used to analyze phase or surface irregularities in optical samples. The monolithic design of the proposed interferometer makes it relatively immune to ambient vibrations.