Four-wave mixing-based orbital angular momentum translation

Abstract

We theoretically study the generation of orbital angular momentum (OAM) based on the four-wave mixing process in a diamond-type homogeneously broadened <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:msup> <mml:mi/> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mn>85</mml:mn> </mml:mrow> </mml:msup> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mi mathvariant="normal">R</mml:mi> <mml:mi mathvariant="normal">b</mml:mi> </mml:mrow> </mml:math> atomic system. We use density matrix formalism at a weak field limit to explain the origin of vortex translation between different optical fields and a generated signal. We show how the singularities, which are omnipresent in the phases of the input optical vortex beams, can be profoundly mapped to atomic coherence in the transverse plane, which holds the origin of OAM translation. This translation process works well even for a moderately intense probe and control field, which enhances medium nonlinearity. The generation and manipulation of OAM of the light beam in a nonlinear medium may have important applications in optical tweezers and quantum information processing systems.