Mayukh Lahiri

Spectral changes of stochastic beams scattered on a deterministic medium

It is well known that scattering of a polychromatic plane wave by a random medium, i.e., by a medium whose refractive index varies randomly with position, may produce frequency shifts of spectral lines. It has been a common perception that a random medium is required for generation of such spectral shifts by scattering. In this Letter we show that such a phenomenon occurs even when the refractive index of the medium is a deterministic function of position. We also show that this phenomenon may be used to obtain information about the structure of a deterministic medium.

Cross-spectral density matrices of polarized light beams

We show that there is no unique form of the cross-spectral density matrix of completely polarized light beams. We present three kinds of such matrices, each of which represents a beam that is completely polarized at every point. Some of the beams do not imitate monochromatic beams, in contrast to the usual assumption made in polarization optics.

Polarization properties of stochastic light beams in the space–time and space–frequency domains

Although the theories of polarization in the space-time and space-frequency domains are somewhat analogous, they have been developed independently, and there is no obvious connection between them. We investigate how they are related.

Theory of quantum imaging with undetected photons

A novel quantum imaging technique has recently been demonstrated in an experiment, where the photon used for illuminating an object is not detected; the image is obtained by interfering two beams, none of which ever interacts with the object. Here we present a detailed theoretical analysis of the experiment. We show that the object information is present only in the interference term and not in the individual intensities of the interfering beams. We also theoretically establish that the magnification of the imaging system depends on two wavelengths: the average wavelength of the photon that illuminates the object and the average wavelength of the photon that is detected. Our analysis affirms that the imaging process is based on the principle that quantum interference occurs when interferometric path information is unavailable.

Beam condition for scattering on random media

Properties of random media are frequently investigated by studying their interactions with stochastic electromagnetic fields. However, a stochastic beam does not necessarily retain its beamlike form on scattering, and the theory of stochastic electromagnetic fields that are not beamlike is rather complicated. In this paper a necessary and sufficient condition is derived for a beam to retain its beamlike form after it is scattered on a stochastic medium. We illustrate the result by an example.

Unpolarized light beams with different coherence properties

We investigate the coherence properties of unpolarized beams. Such beams form a much richer class than has been previously realized. We illustrate our results by examples.

Propagation of electromagnetic beams of any state of spatial coherence and polarization through multilayered stratified media

We present a theory of propagation of a partially coherent and partially polarized electromagnetic beam through a multilayered stratified medium. The analysis shows that spatial coherence and polarization properties of the beam change, in general, on propagation through such a medium. We illustrate the results by an example.

Statistical similarity and cross-spectral purity of stationary stochastic fields

In practical situations, one often generates a beam by superposition of two or more light beams. The beam generated by superposition displays, in general, different spectral properties than do the original beams. However, there are some optical beams, called cross-spectrally pure beams, which can generate a light beam of identical spectral distribution on superposition. The relationship between cross-spectral purity and spatial coherence has been the subject of investigations for some time. Recently, a concept of so-called statistical similarity has been introduced which provides a new way to elucidate complete spatial coherence. In this Letter, we discuss some implications of statistical similarity of an optical field on its cross-spectral purity.

Change in spatial coherence of light on refraction and on reflection

A theory of refraction and reflection of partially coherent electromagnetic beams has been recently developed. In this paper, we apply it to study the change in spatial coherence caused by refraction and by reflection more fully. By considering a Gaussian Schell-model beam, we show that the change is, in general, dependent on the angle of incidence.

Partial polarization by quantum distinguishability

Partial polarization is the manifestation of the correlation between two mutually orthogonal transverse field components associated with a light beam. We show both theoretically and experimentally that the origin of this correlation can be purely quantum mechanical. We perform a two-path first-order (single photon) interference experiment and demonstrate that the degree of polarization of the light emerging from the output of the interferometer depends on path distinguishability. We use two independent methods to control the distinguishability of the photon paths. While the distinguishability introduced in one of the methods can be erased by performing a suitable measurement on the superposed beam, the distinguishability introduced in the other method cannot be erased. We show that the beam is partially polarized only when both types of distinguishability exist. Our main result is the dependence of the degree of polarization on the inerasable distinguishability, which cannot be explained by the classical (non-quantum) theory of light.