Efficient diffraction control using a tunable active-Raman gain medium

We present a new scheme to create all-optical tunable and lossless waveguide using a controllable coherent Raman process in an atomic rubidium vapor in N-type configuration. We employ a Gaussian Raman field and a Laguerre-Gaussian control field to imprint a high-contrast tunable waveguide-like 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 length without diffraction and absorption. Our results on all-optical waveguide based scheme may have potential application in lossless image processing, high contrast biomedical imaging and image metrology.