Gouy phase-matched angular and radial mode conversion in four-wave mixing

Abstract

We investigate the conversion between transverse mode structures in four-wave mixing in a heated rubidium vapour. While angular momentum conservation in this nonlinear process dictates the selection rules for the angular quantum number, the role of the radial quantum number is more esoteric. We demonstrate experimentally that a clean Laguerre-Gauss mode LG p =LG 0 1 can be generated by converting LG 1 0 and LG −1 0 near-infrared pump beams -but only if the length of the atomic medium exceeds the Rayleigh range. In the same regime we also observe a direct transfer of the total radial quantum number from input to generated light modes.

A simple, powerful diode laser system for atomic physics

“…We have developed an economical home-build ECDL solution that can produce hundreds of mW of continuous power with a free-running 100 ms linewidth of (427 ± 7) kHz. It is a single-unit inexpensive source of moderate power for atomic physics experiments involving rubidium and is currently operating as one of the pump lasers in a four-wave mixing experiment 45,46 . We have also detailed cost-and time-effective techniques to determine various useful laser characteristics, including the spectral purity and linewidth.…”

Generalized Orbital Angular Momentum Symmetry in Parametric Amplification

“…Orbital angular momentum (OAM) conservation has been investigated in cavity-free spontaneous [18] and stimulated [19] parametric down-conversion. The nonlinear coupling between different transverse modes is subject to conditions imposed by the spatial overlap between them, giving rise to selection rules that limit the modes allowed in the interaction [20][21][22][23]. When the process is intensified inside an optical resonator, cavity conditions also dictate which modes can survive the loss-gain balance, which can affect both the transverse [24][25][26] and longitudinal [27] mode structure.…”

Spatial distribution of two symmetric four-wave mixing signals induced by Gaussian beams

“…One setting that is commonly used to explore the spatial degrees of freedom of light is that of FWM induced by amplified spontaneous emission in a hot atomic vapor, with a 3-level cascade system [11][12][13][14][15]. In cold atomic samples, FWM was employed to transfer OAM from incident to generated beams in nondegenerate [16] and degenerate [17] atomic systems, to transfer more complicated phase structures (obtained by superimposing LG modes of different orders) [18], and to store the information carried by the spatial structure of light in the ensemble of atoms, and later retrieve it [19,20].…”

“…When the primary objective is the study of the spatial shape of the FWM beam, the usual approach is based on the overlap integral of four paraxial modes [12,14,15,21]. In these cases, the calculations are performed regarding the interaction medium as a channel for the nonlinear process to take place, not possessing degrees of freedom that can affect the output mode superposition.…”

“…In other words, the spatial distribution of the FWM field is fully determined solely by the distributions of the participating beams. With this approach, the theoretical predictions are remarkably accurate [12,15,21]. The role of the spatially dependent nonlinear coherence in the signal generation process was discussed in Ref.…”