N-slit interferometer

The N-slit interferometer is an extension of the double-slit interferometer also known as Young's double-slit interferometer. One of the first known uses of N-slit arrays in optics was illustrated by Newton. In the first part of last century, Michelson described various cases of N-slit diffraction.

Feynman described thought experiments, of two-slit quantum interference, of electrons using Dirac's notation. This approach was extended to N-slit interferometers, by Duarte and colleagues in 1989, using narrow-linewidth laser illumination, that is, illumination by indistinguishable photons. The first application of the N-slit interferometer was the generation and measurement of complex interference patterns. These interferograms are accurately reproduced, or predicted, by the N-slit interferometric equation for either even (N = 2, 4, 6,…), or odd (N = 3, 5, 7,…), numbers of slits.

The N-slit laser interferometer, introduced by Duarte, uses prismatic beam expansion to illuminate a transmission grating, or N-slit array, and a photoelectric detector array (such as a CCD or CMOS) at the interference plane to register the interferometric signal. The expanded laser beam illuminating the N-slit array is single-transverse-mode and narrow-linewidth. This beam can also take the shape, via the introduction of a convex lens prior to the prismatic expander, of a beam extremely elongated in the propagation plane and extremely thin in the orthogonal plane. This use of one-dimensional (or line) illumination eliminates the need of point-by-point scanning in microscopy and microdensitometry. Thus, these instruments can be used as straight forward N-slit interferometers or as interferometric microscopes (see section on microscopy).

The disclosure of this interferometric configuration introduced the use of digital detectors to N-slit interferometry.

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