arXiv:1108.1875 · Physical Review A

Nondiffracting optical beams in a three-level Raman system

Tarak Nath Dey, Jörg Evers

Published Oct 24, 2011• 27 citations

Abstract

Diffractionless propagation of optical beams through atomic vapors is investigated. The atoms in the vapor are operated in a three-level Raman configuration. A suitably chosen control beam couples to one of the transitions, and thereby creates a spatially varying index of refraction modulation in the warm atomic vapor for a probe beam that couples to the other transition in the atoms. We show that a Laguerre-Gaussian control beam allows the propagation of single Gaussian probe field modes as well as multi-Gaussian modes and non-Gaussian modes over macroscopic distances without diffraction. This opens perspectives for the propagation of arbitrary images through warm atomic vapors.

DOI: 10.1103/physreva.84.043842

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arXiv:1108.1875 · Physical Review A

Nondiffracting optical beams in a three-level Raman system

Tarak Nath Dey, Jörg Evers

Published Oct 24, 2011• 27 citations

arXiv HTML PDF

Abstract

DOI: 10.1103/physreva.84.043842

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We present a scheme to create an all-optical tunable and lossless waveguide using a controllable coherent Raman process in an atomic rubidium vapor in an

\mathcal{N}

-type configuration. We employ a Gaussian Raman field and a Laguerre-Gaussian control field to imprint a high-contrast tunable waveguidelike feature inside the atomic medium. We numerically demonstrate that such a waveguide is able to guide arbitrary modes of a weak probe beam to several Rayleigh lengths without diffraction and absorption. Our results on an all-optical waveguide-based scheme may have potential applications in lossless image processing, high-contrast biomedical imaging, and image metrology.

We propose an efficient scheme for the generation of tunable optical waveguides based on atomic vapor in an

N

-type configuration. We exploit both control-field-induced transparency and Kerr-field-induced absorption to produce a flexible probe transparency window otherwise not feasible. We employ a suitable spatial profile of control and Kerr beams to create a high contrast refractive index modulation that holds the key to guiding a weak narrow probe beam. Further, we numerically demonstrate that high-contrast tunable waveguide permits the propagation of different modes of probe beam to several Rayleigh lengths without diffraction. This efficient guiding of narrow optical beam may have important applications in large-density image processing and high-resolution imaging.

We studied Fresnel diffraction of a Laguerre-Gaussian beam

{\text{LG}}_{p,l}

with arbitrary azimuthal

l

and radial

p

indices on a grating induced during its Raman interaction with a spatially periodic pump field in an atomic medium. The diffraction pattern turned out to be more complex than the classical Talbot effect observed when a plane wave illuminates a two-dimensional grating. The simulation results show that, under certain conditions, at distances corresponding to the classical Talbot planes (integer and fractional), periodic amplitude-phase distributions appear. The diffraction patterns are not a probe-field image in the induced grating plane, but a regular array of vortex annular-shaped microbeams with an inhomogeneous intensity distribution depending on the

l

and

p

indices and with a topological charge equal to that of the initial probe beam. The intensity and spatial distribution of diffraction patterns can be controlled by Raman amplification in the induced grating by varying the pump-field intensity or the Raman detuning.