# Multimode collective scattering of light in free space by a cold atomic gas

## TL;DR

This paper investigates collective recoil lasing in cold atomic gases, demonstrating how atomic density gratings and enhanced scattering depend on cloud shape, using numerical simulations to explore multimode light-matter interactions.

## Contribution

It introduces a classical model and simulation approach to study multimode collective scattering in free space, highlighting the role of cloud shape and dynamics.

## Key findings

- Formation of atomic density gratings observed
- Collective enhancement of scattered light demonstrated
- Cloud shape influences scattering dynamics

## Abstract

We have studied collective recoil lasing by a cold atomic gas, scattering photons from an incident laser into many radiation modes in free space. The model consists of a system of classical equations for the atomic motion of N atoms, where the radiation field has been adiabatically eliminated. We performed numerical simulations using a molecular dynamics code, Pretty Efficient Parallel Coulomb Solver or PEPC, to track the trajectories of the atoms. These simulations show the formation of an atomic density grating and collective enhancement of scattered light, both of which are sensitive to the shape and orientation of the atomic cloud. In the case of an initially circular cloud, the dynamical evolution of the cloud shape plays an important role in the development of the density grating and collective scattering. The ability to use efficient molecular dynamics codes will be a useful tool for the study of the multimode interaction between light and cold gases.