Propagation of optical vector vortices of slow light in a coherently prepared tripod configuration

TL;DR

This paper explores how optical vector vortices carrying orbital angular momentum propagate as slow light in a coherently prepared four-level atomic system, revealing tunable polarization and intensity dynamics.

Contribution

It introduces a novel method to control slow-light vector vortex properties through a tripod atomic configuration with phase-dependent coherence.

Findings

OAM is mapped onto the medium, creating azimuthal absorption patterns.

Control field reduces losses and enables polarization state manipulation.

Polarization states evolve periodically, allowing tunable control over vortex dynamics.

Abstract

We investigate the propagation of optical vector vortices of slow light in a coherently prepared four-level tripod atomic system. The vector vortex consists of superposed pulse pairs with opposite circular polarizations and orbital angular momentum (OAM) charges $\pm l$, weakly interacting with an atomic medium initially prepared in a coherent superposition of two ground states. A third unoccupied state is coupled to a stronger control laser without OAM, creating a phase-dependent configuration. In the linear regime, the vortex OAM is mapped onto the medium, producing symmetrical azimuthally structured absorption patterns, with losses significantly reduced by the control field. For small detunings, complementary spatially dependent amplification and absorption occur for the two circular polarization components. This OAM-structured coherence induces a dynamical anisotropy, affecting both the intensity and polarization of the slow-light vortex. Polarization states evolve periodically between left-circular, linear, and right-circular polarizations during propagation. Once the beam reaches a stationary regime, the ring-shaped intensity transforms into a petal-like structure, and the final polarization states stabilize according to the initial superposition. The rate of polarization transitions is tunable via the control field strength, demonstrating flexible control over slow-light vector vortex dynamics.