Linear and nonlinear propagation of cylindrical vector beam through a non-degenerate four level atomic system

TL;DR

This paper explores how phase-induced susceptibilities affect the propagation of cylindrical vector beams in a non-degenerate four-level atomic system, revealing phenomena like polarization rotation, self-focusing, and defocusing with potential applications in microscopy and optical trapping.

Contribution

It introduces a detailed analysis of phase-dependent linear and nonlinear susceptibilities for vector beams in a four-level atomic system, highlighting control mechanisms for beam propagation.

Findings

Phase shift influences loss, gain, and polarization rotation of vector beams.

Nonlinear effects cause self-focusing and defocusing phenomena.

Formation of smaller spots with moderate gain through chain-like self-focusing.

Abstract

We investigate the phase-induced susceptibilities for both components of the probe vector beam (PVB) within an atomic system. The atoms are prepared in a non-degenerate four-level configuration. The transitions are coupled by a $\pi$ polarized control field and two orthogonally polarized components of a PVB. We show that the linear susceptibility of the medium depends on the phase shift between the control field and PVB, characterizing loss or gain in the system. Additionally, the phase shift causes polarization rotation in the vector beams (VBs) as they propagate. We further study the effect of nonlinearity on the VB propagation through the medium for a couple of Rayleigh lengths. The self-focusing and defocusing phenomena are observed for radial, azimuthal, and spiral VBs. The special chain-like self-focusing and defocusing leads to the formation of consecutive smaller spot sizes with moderate gain. Therefore, the mechanism of control of susceptibility and self-focusing may hold promise for applications such as transitioning from an absorber to an amplifier, high-resolution microscopy, and optical trap systems.