# Laser M\"ossbauer spectroscopy of ^{229}Th

## TL;DR

This paper extends M"ossbauer spectroscopy into the optical range using a vacuum ultraviolet laser to study thorium-229 in crystals, revealing doping sites, local structures, and nuclear environment details relevant for nuclear clock development.

## Contribution

It introduces a laser-based M"ossbauer spectroscopy method for low-energy nuclear transitions, identifying doping sites and local structures of thorium-229 in crystals.

## Key findings

- Discovered four distinct thorium doping sites.
- Determined electric field gradients at each site.
- Studied isomeric state lifetime and laser quenching effects.

## Abstract

M\"ossbauer spectroscopy is widely used in biochemistry, geology, and solid-state physics to obtain structural information on materials. Here, we extend this technique into the optical range using a vacuum ultraviolet laser to probe the low-energy nuclear transitions of thorium-229, doped in calcium fluoride crystals. We discover four distinct doping sites for the thorium ions, determine the characteristic electric field gradients emerging in the interaction with the host crystal, and identify the microscopic structure of the two dominant configurations. Site-selective laser excitation allows to study the isomeric state lifetime and laser-induced quenching for all sites. This laser-based M\"ossbauer spectroscopy provides a powerful probe of the nuclear environment, yielding foundational data for designing future solid-state nuclear clocks.