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arXiv:2404.10280 · Physical Review A

Efficient diffraction control using a tunable active-Raman gain medium

Sandeep Sharma

Published Feb 1, 2023• 3 citations
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Abstract

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.

DOI
10.1103/physreva.107.023701

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•Dec 1, 2011•0 citations
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 N\mathcal{N}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 NNN-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 theoretically demonstrate an efficient scheme to build a microwave (MW) assisted optical waveguide in an inhomogeneously broadened vapor medium that is made of active 87 Rb atoms and inactive buffer gas atoms. We exploit the sensitive behaviour of MW field coupled between highly excited Rydberg states to create distinctly responsive and tunable atomic waveguide. The buffer gas induced collision further manipulates the features of the waveguide by widening the spatial transparency window and enhancing the contrast of the refractive index. We numerically solve Maxwell's equations to demonstrate diffractionless propagation of 5 micrometer narrow paraxial light beams of arbitrary mode to several Rayleigh lengths. The presence of the buffer gas significantly enhances output intensity of the diffraction controlled light beam from 10 percent to 54 percent. This efficient diffraction elimination technique has important applications in high-resolution imaging and high-density optical communication.
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.
We propose a novel scheme to realize an optical waveguide induced by an active Raman gain (ARG) process in a four-level N-type atomic system. Because of the nature of the ARG, there are two distinct features related to the waveguide: i) It is not absorptive, on the contrary, weak gain is presented; ii) It can be improved by the Doppler effect in the sense that the dispersion is enhanced while the gain is further reduced. This is in sharp contrast to the previously considered schemes where usually the optical induced waveguide is passive and is severely attenuated by the Doppler effect. We then study the paraxial light propagation in the waveguide which shows that the propagation dynamics is lossless and diffractionless.
This thesis presents the applications of some of the coherent processes in a three-level atomic system, to control spatial and temporal properties of a signal pulse. We use two Raman absorption resonances in rubidium vapor separated by a few MHz to achieve a rapidly tunable slow-light system. We control the slow-light characteristics all-optically by tuning the frequency and power of a coupling beam. A dual absorption slow-light system is known to cause less pulse broadening than a single transmission resonance system, and thus, a tunable double absorption system is advantageous. We use a four-wave mixing process to demonstrate pulse storage in rubidium vapor for times much greater than the pulse width. We demonstrate storage of both the temporal and spatial profile of the pulse. We overcome the diffusion of spatial information during the storage in warm atomic vapor by storing the Fourier transform of the image instead of an image with a flat phase. The Raman absorption resonance is also used to control the transverse refractive index profile of the signal beam. The refractive index of the signal interacting with a coupling beam in a Raman process is dependent on the coupling beam intensity. We use a first order Laguerre-Gaussian (LG01) coupling beam to create a waveguide like transverse refractive index profile. We demonstrate propagation of a focused signal beam for lengths much greater than the Rayleigh length. Finally, we demonstrate a dual absorption atomic prism, which is capable