# The interplay between thermal Rydberg gases and plasmas

## TL;DR

This paper explores how plasma formation due to ionized Rydberg atoms causes optical bistability in thermal cesium gases, combining experiments and modeling to understand the underlying ionization and avalanche processes.

## Contribution

It provides the first detailed experimental and numerical analysis linking plasma formation to optical bistability in thermal Rydberg gases, highlighting plasma effects as a limiting factor.

## Key findings

- Plasma formation causes optical bistability in thermal Rydberg gases.
- Measured plasma frequency confirms plasma's role in bistability.
- Numerical model accurately reproduces experimental spectra.

## Abstract

We investigate the phenomenon of bistability in a thermal gas of cesium atoms excited to Rydberg states. We present both measurements and a numerical model of the phenomena based on collisions. By directly measuring the plasma frequency, we show that the origin of the bistable behavior lies in the creation of a plasma formed by ionized Rydberg atoms. Recombination of ions and electrons manifests as fluorescence which allows us to characterize the plasma properties and study the transient dynamics of the hysteresis that occurs. We determine scaling parameters for the point of plasma formation, and verify our numerical model by comparing measured and simulated spectra. These measurements yield a detailed microscopic picture of ionization and avalanche processes occurring in thermal Rydberg gases. From this set of measurements, we conclude that plasma formation is a fundamental ingredient in the optical bistability taking place in thermal Rydberg gases and imposes a limit on usable Rydberg densities for many applications.