# Propagation of ultra-short, resonant, ionizing laser pulses in rubidium vapor

## TL;DR

This paper models and simulates how ultra-short, resonant laser pulses propagate in rubidium vapor, leading to plasma channel formation, with implications for plasma accelerators.

## Contribution

It introduces a simple theoretical framework for nonlinear response and explores pulse propagation and plasma channel formation in rubidium vapor.

## Key findings

- Nonlinear self-channeling produces a continuous plasma channel.
- Optimal pulse energy and focusing conditions for plasma channel formation.
- Comparisons with atmospheric laser filamentation phenomena.

## Abstract

We investigate the propagation of ultra-short laser pulses in atomic rubidium vapor. The pulses are intensive enough to ionize the atoms and are directly resonant with the 780 nm $D_2$ line. We derive a relatively simple theory for computing the nonlinear optical response of atoms and investigate the competing effects of strong resonant nonlinearity and ionization in the medium using computer simulations. A nonlinear self-channeling of pulse energy is found to produce a continuous plasma channel with complete ionization. We evaluate the length, width and homogeneity of the resulting plasma channel for various values of pulse energy and initial focusing to identify regimes optimal for applications in plasma-wave accelerator devices such as that being built by the AWAKE collaboration at CERN. Similarities and differences with laser pulse filamentation in atmospheric gases are discussed.