3 - Two-Beam Interferometers

Abstract

This chapter discusses the two-beam interferometers. To make measurements using interference, a special optical arrangement is required in which two beams traveling along separate paths are made to interfere. Two methods are commonly used to obtain two beams from a single source—wavefront division and amplitude division. Wavefront division uses apertures to isolate two beams from separate portions of the primary wavefront. And in amplitude division, two beams are derived from the same portion of the original wavefront. The chapter discusses various types of two-beam interferometers. First of them is the Rayleigh interferometer, which uses wavefront division to produce two beams from a single source. It is simple and stable but has the disadvantage that the interference fringes are very closely spaced. The second one is the Michelson interferometer, the beam from the source is divided at a semi-reflecting coating on the surface of a plane-parallel glass plate. The third two-beam interferometer is the Mach–Zehnder interferometer. It uses two beam splitters and two mirrors to divide and recombine the beams. It is widely used for studies of fluid flow, heat transfer, and the temperature distribution in plasmas and fourth two-beam interferometer is Sagnac interferometer, in which the two beams traverse the same path in opposite directions.