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Transverse Spin and Transverse Momentum in Structured Optical Fields

ecently it has been recognized that in addition to the conventional longitudinal AM, structured (inhomogeneous) optical fields can exhibit helicity-independent transverse SAM and an unusual spin (polarization)-dependent transverse momentum, the so-called Belinfante’s spin momentum. Unlike the usual canonical (orbital) momentum, this transverse spin-momentum is a virtual entity, which neither transfers energy nor exerts pressure on dipolar particles. Such highly nontrivial structure of the momentum and spin densities are observed in the evanescent fields (e.g., for surface plasmon-polaritons at dielectric-metal interfaces) and leads to the optical spin-momentum locking in surface optical modes, similar to that observed for electrons in topological insulators. We study some of these effects in strongly coupled systems.

Strong Coupling in Birefringent Cavities

We study the strong coupling regime where the orthogonal modes of a birefringent crystal are coupled via an intracavity rotator. The coupling leads to the anticrossing of the relevant dispersion branches. We demonstrate the inherent ability of such devices for resolving small amgles.

Nano Optics and Plasmonics

Plasmonics is the gateway to the nano world since it has the inherent ability to beat the Rayleigh limit. We explore different facets of nano plasmonics ranging from gap plasmons to superresolution, perfect imaging and total tranfer of incident light to localized and surface/guided modes. Wigner delay and the Goos-Hanchen shift through such structures are also studied.

Critical Coupling and Coherent Perfect Absorption (CPA)

A critically coupled system absorbs all the incident radiation leading to null scattering. Critical coupling with two or more beams is referred to as CPA where destructive interference cancels out all the scattered light in a narrow frequency range.Efforts are on to broaden the CPA resonance and to extend it to incoherent light. Success in this area could be vital for photo-voltaic applications.

Subluminal and Superluminal Propagation of Light

Dispersion management is the key to the control of velocity of light pulses. We study such control in heterogeneous
and left handed media, Fabry-Perot cavities, periodic and quasiperiodic structures.

Left Handed (Negative Refractive Index) Media and Other Metamaterials

The left handed materials were theoretically discovered by Vaselago in 1968 (JETP), but have been realized only recently. These have exotic properties capable of leading to perfect lensing, anomalous Doppler shift, etc. We show that such materials can lead to highly subluminal propagation.
There has been intensive activity on spatial Kramers-Kronig media where one deals with spatial cordinates having intrinsic antireflection properties. Such media are yet to be realized. We study some of the nonreciprocity aspects of such media.

Whispering Gallery Modes of Microspheres

Micron sized spheres can support whispering gallery modes with extremely high quality factors (~1010) and local field enhancements. We probe the use of such modes for nonlinear optics and cavity quantum electrodynamics.

Optical Theorem and Nonreciprocity in Standard and PT-Symmetric Media

The reflectivity of a one dimensional system with absorption and broken inversion symmetry is sensitive to whether light is incident from left or right. We study such effects in stratified media and in BEC, where the properties can be engineered by laser light.

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UEC Collaborators

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