The possibility to easily control the features of the light in the reference channel without disturbing the light in the object channel popularized the Mach–Zehnder configuration in holographic interferometry. Mach–Zehnder interferometers are also used to study one of the most counterintuitive predictions of quantum mechanics, the phenomenon known as quantum entanglement. Mach–Zehnder modulators are incorporated in monolithic integrated circuits and offer well-behaved, high-bandwidth electro-optic amplitude and phase responses over a multiple-gigahertz frequency range. Mach–Zehnder interferometers are used in electro-optic modulators, electronic devices used in various fiber-optic communication applications. It is frequently used in the fields of aerodynamics, plasma physics and heat transfer to measure pressure, density, and temperature changes in gases. The Mach–Zehnder interferometer's relatively large and freely accessible working space, and its flexibility in locating the fringes has made it the interferometer of choice for visualizing flow in wind tunnels and for flow visualization studies in general. : 18 In most cases, the fringes would be adjusted to lie in the same plane as the test object, so that fringes and test object can be photographed together. In Fig. 2, we see that the fringes can be adjusted so that they are localized in any desired plane. Localized fringes result when an extended source is used. By appropriately adjusting the mirrors and beam splitters, the fringes can be localized in any desired plane.Ĭollimated sources result in a nonlocalized fringe pattern. Localized fringes result when an extended source is used in a Mach–Zehnder interferometer. The result is that light travels through an equal optical path length in both the test and reference beams leading to constructive interference. In this orientation, the test and reference beams each experience two front-surface reflections, resulting in the same number of phase inversions. The reflecting surfaces of the beam splitters would be oriented so that the test and reference beams pass through an equal amount of glass. Note also the precise orientation of the beam splitters. As seen in Fig. 1, a compensating cell made of the same type of glass as the test cell (so as to have equal optical dispersion) would be placed in the path of the reference beam to match the test cell. White light in particular requires the optical paths to be simultaneously equalized over all wavelengths, or no fringes will be visible (unless a monochromatic filter is used to isolate a single wavelength). If the source has a low coherence length then great care must be taken to equalize the two optical paths. In contrast to the well-known Michelson interferometer, each of the well-separated light paths is traversed only once. The Mach–Zehnder check interferometer is a highly configurable instrument. 5.2 Other flow visualisation techniques.
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