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Physical Chemistry Chemical Physics

Modulation of spatial Raman gain induced by Laguerre–Gaussian vortex beams

Qi MING, Zhenxing Fu

Published Jan 1, 2026• 0 citations
Publisher

Abstract

(1), 013701, which focused on overall optical gain in open-loop configurations, our study examines how structured light modulates the spatial distribution of Raman gain. Using a density-matrix approach, we numerically obtain two-dimensional maps and cross-sectional profiles of Raman gain. The results show that three parameters-the orbital angular momentum (OAM) of the LG beam, the single-photon detuning, and the relative phase of the control fields-collectively determine the spatial morphology of the gain. OAM controls the transition between single-lobe and multi-lobe structures, modulates the gain magnitude and spatial complexity, and the relative phase induces rotational or mirror-symmetric transformations. This work provides the first systematic analysis of spatial Raman-gain modulation in a closed-loop three-level system, demonstrating the strong capability of structured light to tailor nonlinear gain processes. The findings extend the theoretical framework beyond PRA 2024 and offer insights for spatially selective amplification and structured-light-based photonic device design.

DOI
10.1039/d5cp03598h

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(1), 013701, which focused on overall optical gain in open-loop configurations, our study examines how structured light modulates the spatial distribution of Raman gain. Using a density-matrix approach, we numerically obtain two-dimensional maps and cross-sectional profiles of Raman gain. The results show that three parameters-the orbital angular momentum (OAM) of the LG beam, the single-photon detuning, and the relative phase of the control fields-collectively determine the spatial morphology of the gain. OAM controls the transition between single-lobe and multi-lobe structures, modulates the gain magnitude and spatial complexity, and the relative phase induces rotational or mirror-symmetric transformations. This work provides the first systematic analysis of spatial Raman-gain modulation in a closed-loop three-level system, demonstrating the strong capability of structured light to tailor nonlinear gain processes. The findings extend the theoretical framework beyond PRA 2024 and offer insights for spatially selective amplification and structured-light-based photonic device design.
An efficient scheme for controlling the spatial Raman gain is proposed in a cold atomic ensemble with a four-level N-typed configuration. The cold atoms are driven by the Laguerre-Gaussian (LG) vortex beams. Considering the control and driving fields are vortex beams and using experimentally achievable parameters, we identify the condition under which the topological charges (TCs) allows us to manipulate the radial distribution of the Raman gain spectra. It is found that the spatial Raman gain can be effectively controlled via adjusting the relevant optical parameters. Furthermore, we show interesting optical properties of vortex-induced transparency(VIT) and vortex-induced gain (VIG) via controlling the spatial Raman-gain spectrum. Finally we show that the azimuthal modulation of the Raman gain profiles can be realized and controlled when the control field consists of a travelling-wave (TW) field and two optical vortex fields. Our scheme may provide a feasible approach for constructing novel vortex beams based on cold atomic ensemble.
Abstract We have proposed a double scheme for the efficient generation and control of spatial four-wave mixing (FWM)-induced ultraviolet light via optical angular momentum transfer from a vortex-field (Laguerre–Gaussian (LG) beam) applied once to the excited transition of the first two-photon ladder and then in the uppermost transition of the three-photon ladder in the FWM-loop configuration of a five-level atomic excitation mechanism. In both the LG-cases, at the conditions of resonant and off-resonant detunings of the two coherent fields with high Rabi frequencies guiding the multi-photon excitation route in the system, it has been shown that the vortex FWM light can propagate either in the superluminal or in the subluminal regime depending upon ‘turned-off’ and ‘turned-on’ conditions of a Raman field outside the FWM-loop, respectively. Such switching phenomenon is the most interesting outcome of the present study along with the significant phase-twisting effects as manifested in the helical phase patterns in both the LG-cases. Thus, the practical implementation of the present model under a cold atomic environment paves up a novel way of obtaining structured high-dimensional light transfer process based on the mechanism of nonlinear photonics, which might have potential applications in quantum information processing and technology in the near future.
Abstract We study high-resolution atomic localization in a multilevel atomic system driven simultaneously by a Gaussian and a Laguerre–Gaussian (LG) beam. The coexistence of the two fields creates a hybrid coupling landscape in which the Gaussian beam supplies radial confinement, while the LG beam contributes an orbital angular momentum (OAM)-dependent azimuthal modulation. By solving the steady-state density-matrix equations, we show that the resulting localization patterns contain mixed spatial harmonics whose structure is set by the topological charge, beam waist, and probe detuning. The OAM index determines the angular symmetry of the localized absorption features, whereas the beam waist controls their radial extent. Probe detuning provides an additional tuning mechanism that alters the contrast and geometry of the localization regions. These results highlight how structured light fields can be used to engineer controllable spatial localization in atomic media, with relevance to precision metrology, spatially resolved quantum control, and structured-light sensing.
Abstract Spatially structured optical reflection and phase modulation in cavity quantum electrodynamics present a pathway to programmable control of structured light and topological photonic states. This study examines the spatial response of a three-level atom–assisted single-sided cavity, driven by a composite vortex control field, by analyzing the transverse distributions of the reflection coefficient and reflected-phase shift as influenced by variations in cavity decay rate, external coupling strength, and the orbital angular momentum (OAM) content of the driving fields. The control Rabi frequency Ω l ( r , ϕ ) , which inherits the doughnut-shaped amplitude and helical phase of vortex beams, results in position-dependent atomic coherence and effective cavity susceptibility, imprinting ring-like or petal-like textures onto both reflectivity and phase. For symmetric counter-rotating vortices with l 1 = − l 2 = 1 − 4 , the reflection forms 2 l -petal patterns, and the phase exhibits complementary 2 l -fold lobes with sharp phase-gradient boundaries dictated by cos ⁡ ( 2 l ϕ ) interference, while central singular features intensify with OAM order. In the case of asymmetric OAM pairs, rotational symmetry is disrupted, and the spatial spectra are primarily determined by Δ l = 3 and 5, respectively, resulting in distorted threefold and fivefold modulations with localized singular defects and star-like phase topology.
The effect of the orbital angular momentum (OAM) of light beams on the optical bistability (OB) phenomenon has been investigated in a three-level quantum system. In a first step, we consider a Λ -type configuration in which the coupling field is assumed as a Laguerre–Gaussian (LG) beam. It is shown that the OB strength spatially depends on the intensity profile as well as the topological charge (TC) of the light beam. In a second scheme, we apply a strong microwave field to the lower level transition and obtain an analytical expression for the OB behavior of the probe field in the presence of an LG field in the multi-photon resonance condition. We analytically obtain a generalized input–output bistability relation for the systems containing the LG beam. More complicated phase-dependent OB profiles can be obtained for higher order LG modes due to the OAM transfer and classical interference between the generated field and applied fields. The results of this paper may provide a potential application of OB in generating simultaneously reconfigurable sets of various optical logic gates in the same structure, as well as in enhancing the capacity of fast volatile bit-level optical memories.
Structured light associated with Laguerre-Gauss (LG) modes carrying orbital angular momentum (OAM) is an important tool in many different areas, ranging from optical tweezers to classical and quantum communication systems [1]. In this work we demonstrated the amplification and the storage of light with OAM employing the magnetically assisted gain mechanism. This gain mechanism is based on the manipulation of the dark-state created by a coupling and a probe beam in the Zeeman sublevels of a degenerate two-level system and can provide single-pass optical gain exceeding 100% [2], [3].