# Nonlinear magneto-optical rotation with parametric resonance

## TL;DR

This paper explores nonlinear magneto-optical rotation in rubidium vapor under modulated magnetic fields, revealing a novel parametric resonance mechanism that enhances polarization rotation signals.

## Contribution

It introduces a new understanding of NMOR involving parametric resonance, supported by experimental and theoretical analysis, expanding the knowledge of magnetic field effects on atomic polarization.

## Key findings

- Resonances observed at both small and large static magnetic fields.
- Enhanced polarization rotation signals through combined passive and atom-induced effects.
- Theoretical simulations confirm the experimental observations and explain the underlying mechanisms.

## Abstract

We report on investigations of nonlinear magneto-optical rotation (NMOR) in rubidium vapor subjected to a modulated magnetic field and continuous-wave (CW) laser-light illumination. By superimposing modulation and a static (DC) magnetic field, we demonstrate the appearance of resonances at both small and large (compared to the ground-state relaxation rate) values of the static field. Since in conventional NMOR, there is no rotation at high fields, this suggests an existence of a novel mechanism generating anisotropy in the considered case, which we identify as parametric resonance. The experiments are performed using light of small ellipticity and rotation signals are significantly enhanced by combining atom-induced polarization rotation with a passive rotation induced with a wave plate. All the observations are supported with theoretical simulations. The density-matrix formalism and angular-momentum probability surfaces are used to provide intuitive explanation of the observed signals.