Controllable linear $\pi$-phase modulation in a thermal atom vapor without diffraction or absorption

TL;DR

This paper proposes a method for achieving significant, controllable phase modulation of a probe light in a thermal atomic vapor, eliminating diffraction and absorption effects, with potential for practical optical applications.

Contribution

It introduces a scheme that uses thermal atomic motion and incoherent pumping to enable uniform, controllable phase shifts without diffraction or absorption in a thermal vapor.

Findings

Achieves strong, uniform phase modulation independent of probe profile.

Eliminates paraxial diffraction through atomic thermal motion.

Compensates residual absorption with incoherent pumping.

Abstract

A scheme is proposed to achieve substantial controllable phase modulation for a probe field propagating through a thermal atomic vapor in double-$\Lambda$ configuration. The phase modulation is based on the linear susceptibility of the probe field, paraxial diffraction is eliminated by exploiting the thermal motion of atoms, and residual absorption is compensated via an incoherent pump field. As a result, a strong controllable uniform phase modulation without paraxial diffraction is achieved essentially independent of the spatial profile or the intensity of the probe field. This phase shift can be controlled via the intensities of the control or the incoherent pump fields. A possible proof-of-principle experiment in alkali atoms is discussed.