Chapter 2 - Dirac Optics

Abstract

This chapter describes the various aspects of Dirac optics. Dirac introduced the nomenclature of ket vectors and bra vectors that are mirror images of each other. The probability amplitude is described by the braket, which is a complex number. The Dirac notation, though originally applied to the propagation of single particles also applies to describe the propagation of ensembles of coherent, or indistinguishable, photons. The N-slit interferometer can be configured with a variety of lasers, including tunable lasers. One requirement is that the laser to be utilized must emit in the narrow-linewidth regime and in a single transverse mode with a near-Gaussian profile. It is observed that when a wide slit is used to select the central portion of the elongated Gaussian beam, the interaction of the coherent laser beam with the slit results in diffraction prior to the illumination of the transmission grating. The interferometric can be used to characterize this diffraction. This is done by dividing the wide slit into hundreds of smaller slits. It is suggested that for spectrophotometers and wavelength meters based on dispersive elements, such as diffraction gratings and prism arrays, the dispersion should be as large as possible because that enables a higher-wavelength spatial resolution.