Trans-Spectral Orbital Angular Momentum Transfer via Four-Wave Mixing in Rb Vapor

TLDR

The study demonstrates transfer of orbital angular momentum from near‑infrared pump beams to blue light via four‑wave mixing in rubidium vapor. By shaping 780 nm and 776 nm pump beams with a spatial light modulator, the authors control the phase and intensity of the 420 nm output in the four‑wave‑mixing cascade. The experiment shows complete transfer of orbital angular momentum to the blue beam, with complex pump profiles generating phase‑matched spatial modes, highlighting potential for phase‑information storage in atomic gases.

Abstract

We report the transfer of phase structure, and in particular of orbital angular momentum, from near-infrared pump light to blue light generated in a four-wave-mixing process in 85Rb vapour. The intensity and phase profile of the two pump lasers at 780nm and 776nm, shaped by a spatial light modulator, influences the phase and intensity profile of light at 420nm which is generated in a subsequent coherent cascade. In particular we oberve that the phase profile associated with orbital angular momentum is transferred entirely from the pump light to the blue. Pumping with more complicated light profiles results in the excitation of spatial modes in the blue that depend strongly on phase-matching, thus demonstrating the parametric nature of the mode transfer. These results have implications on the inscription and storage of phase-information in atomic gases.