Laser locking to the 199Hg clock transition with 5.4x10^(-15)/sqrt(tau) fractional frequency instability

TL;DR

This paper demonstrates laser locking to the 199Hg clock transition using ultrastable lasers, achieving record fractional frequency stability suitable for precision timekeeping and frequency standards.

Contribution

It introduces a method to lock lasers to the 199Hg clock transition with unprecedented stability, utilizing ultrastable cavities and optical lattice trapping in the Lamb-Dicke regime.

Findings

Achieved fractional frequency stability of 5.4x10^(-15)/sqrt(tau) for tau<=400s.

Demonstrated a flicker noise limited fractional frequency instability of 4x10^(-16) per cavity.

Produced a spectral line with a width less than 15Hz at 265.6 nm.

Abstract

With Hg atoms confined in an optical lattice trap in the Lamb-Dicke regime, we obtain a spectral line at 265.6 nm in which the full-width at half-maximum is <15Hz. Here we lock an ultrastable laser to this ultranarrow clock transition and achieve a fractional frequency stability of 5.4x10^(-15)/sqrt(tau) for tau<=400s. The highly stable laser light used for the atom probing is derived from a 1062.6 nm fiber laser locked to an ultrastable optical cavity that exhibits a mean drift rate of -6.0x10^(-17) s^(-1) (or -16.9 mHz.s^(-1) at 282 THz) over a five month period. A comparison between two such lasers locked to independent optical cavities shows a flicker noise limited fractional frequency instability of 4x10^(-16) per cavity.