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.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).These interferometers, originally introduced for applications in imaging, are also useful in optical metrology and have been proposed for secure optical communications in free space, between spacecraft. This is due to the fact that propagating N-slit interferograms suffer catastrophic collapse from interception attempts using macroscopic optical methods such as beam splitting. Recent experimental developments include terrestrial intra-interferometric path lengths of 35 meters and 527 meters.