# Detection of radiation torque exerted on an alkali-metal vapor cell

## TL;DR

This study presents a torsion balance method to detect radiation torque on a cesium vapor cell, revealing insights into angular momentum transfer from polarized gaseous atoms to a solid surface.

## Contribution

It introduces a novel experimental setup using a torsion balance to measure radiation torque exerted on a spin-polarized vapor cell, advancing understanding of spin-transfer at the gas-solid interface.

## Key findings

- Large radiation torque observed when hyperfine levels are optically pumped.
- Torque varies with light helicity and magnetic field conditions.
- Potential to explore spin-transfer mechanisms at the atomic level.

## Abstract

We have developed a torsion balance to detect the rotation of a cell containing spin-polarized gaseous atoms to study angular momentum transfer from gaseous atoms to solid. A cesium vapor cell was hung from a thin wire in a vacuum chamber, and irradiated from the bottom with circularly polarized light tuned to the $D_2$ transition to polarize cesium atoms in the cell. By varying the light helicity at the resonance frequency of the torsion balance, we induced forced rotational oscillation of the cell and detected radiation torque exerted on the cesium vapor cell through the cesium atoms inside. The torque was particularly large when both hyperfine levels of cesium atoms were optically pumped with application of a longitudinal magnetic field. Further detailed study will provide new insights into spin-transfer processes at the gas-solid interface.