# Observation of Optomechanical Strain in a Cold Atomic Cloud

## TL;DR

This paper demonstrates how intense laser illumination causes measurable optomechanical strain in cold atomic clouds, revealing a new force distinct from traditional scattering and dipole forces, with potential for tunable inter-particle interactions.

## Contribution

It reports the first observation of optomechanical strain in cold atomic clouds and characterizes a novel optomechanical force separate from known optical forces.

## Key findings

- Atomic clouds act as lenses focusing the laser beam.
- The optomechanical force depends on the density profile of the cloud.
- The strain saturates, limiting momentum transfer.

## Abstract

We report the observation of the optomechanical strain applied to thermal and to quantum degenerate $^{87}\text{Rb}$ atomic clouds when illuminated by an intense, far detuned homogenous laser beam. In this regime the atomic cloud acts as a lens which focuses the laser beam. As a back action, the atoms experience a force opposite to the beam deflection, which depends on the atomic cloud density profile. We experimentally demonstrate the basic features of this force, distinguishing it from the well-established scattering and dipole forces. The observed strain saturates, ultimately limiting the momentum impulse that can be transferred to the atoms. This optomechanical force may effectively induce inter-particle interactions, which can be optically tuned.