A novel one-beam interferometer based on beam folding is described. The device resembles a Mach–Zehnder interferometer in which the two arms are located together in one collimated beam. Different halves of the same beam interfere with the help of a mirror—with its reflecting surface along the axis of the optical system—placed near the focal plane of the imaging lens. Phase-delay control is achieved by application of an electrical potential to a Pockels cell, which permits the use of techniques of phase-stepping interferometry.
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