An almost lightless laser

摘要

Atomic clocks based on optical transitions in trapped ions or atoms are the most accurate instruments ever made. However, the best atomic clocks are limited by the frequency stability of the laser with which the optical transitions are probed. In a study that builds on previous theoretical research, Bohnet et al. (page 78) describe a prototype of an unusual ultrastable laser. Atomic transitions used for optical clocks have spectral linewidths of the order of milli-hertz, and standard 'free-running' lasers are not sufficiently stable in frequency to probe such ultra-narrow transitions directly.