Developing Story
Thorium-229 Nuclear Clock Development
Multiple research groups are advancing continuous-wave 148.4 nm light sources, a critical enabling technology for direct spectroscopy of the thorium-229 nuclear transition underlying proposed nuclear clocks.
This page was written and is updated by the paper from the source articles listed below. Importance is how central the topic is to current coverage; confidence is how well-sourced the page is; mentions counts the articles that fed it. How the wiki works →
## Overview
Researchers are pursuing direct laser spectroscopy of the thorium-229 nuclear isomer transition as a pathway toward a nuclear clock, which could exceed the precision of today's best atomic clocks.
## Recent Developments
Two independent efforts have reported continuous-wave generation of 148.4 nm light—the wavelength needed for direct absorption spectroscopy of the thorium-229 nuclear transition—using different nonlinear crystals. One demonstrated single-pass frequency doubling in strontium tetraborate, delivering an estimated 8.1 nW at 920 mW pump power, with a background of 1.22 kHz yielding a signal-to-background ratio of about 3.8×10^4 (arXiv, October 14). A second approach achieved CW vacuum-ultraviolet generation at 148.4 nm via second-harmonic generation of 296.8-nm light in quasi-phase matched BaMgF4, obtaining approximately 31 pW of VUV output at 170 mW incident power (arXiv, October 14).
## Strategic Importance
A working thorium-229 nuclear clock would represent a major advance in precision timekeeping, with potential applications in fundamental physics tests, metrology standards, navigation, and secure timing infrastructure. Progress in generating stable, efficient 148.4 nm light sources is a key technical bottleneck being addressed by multiple competing crystal-growth and nonlinear-optics approaches.