Optical non-linearity in a dynamical Rydberg gas

TL;DR

This paper investigates the optical non-linearity in a Rydberg gas using EIT, revealing how attractive dipole interactions and scan direction influence the non-linear response, with measurable third- and second-order susceptibilities.

Contribution

It demonstrates the transient optical non-linearity in a Rydberg gas and explains the effects of scan direction and motional dynamics on the non-linear response.

Findings

Measured third-order non-linearity $oldsymbol{ ext{chi}^{(3)}=5 imes 10^{-7}}$ m$^2$V$^{-2}$

Observed second-order non-linearity $oldsymbol{ ext{chi}^{(2)}=5 imes 10^{-6}}$ mV$^{-1}$ in reverse scan

Contrasting behaviors explained by motional effects and Rydberg pair excitation

Abstract

We use the technique of electro-magnetically induced transparency (EIT) to probe the effect of attractive dipole-dipole interactions in a highly excited Rydberg gas. The transient character of the EIT response is investigated by rapidly scanning the probe laser through resonance. We characterize the resulting cooperative optical non-linearity as a function of probe strength, density and scan direction. For the 58D$_{5/2}$ Rydberg state, an atom density of $1.6\times10^{10} $cm$^{-3}$ and a positive frequency scan we measure a third-order non-linearity of $\chi^{(3)}=5\times 10^{-7}$ m$^2$V$^{-2}$. For the reverse scan we observe a second order non-linearity of $\chi^{(2)}=5\times 10^{-6}$ mV$^{-1}$. The contrasting behaviour can be explained in terms of motional effects and resonant excitation of Rydberg pairs.