Stability limits of an optical frequency standard based on free Ca atoms

TL;DR

This paper assesses the short-term stability limits of a calcium-based optical frequency standard using free atoms, highlighting the impact of technical noise and the Dick effect on stability.

Contribution

It provides a quantitative analysis of the stability limits of a free calcium atom optical clock and introduces a method to measure technical noise without a second clock or frequency comb.

Findings

Filtering the clock laser reduces the optical Dick effect.

Technical noise is the main limiting factor for stability.

The method allows direct measurement of technical noise.

Abstract

We have quantified a short term instability budget for an optical frequency standard based on cold, freely expanding calcium atoms. Such systems are the subject of renewed interest due to their high frequency stability and relative technical simplicity compared to trapped atom optical clocks. By filtering the clock laser light at 657 nm through a high finesse cavity, we observe a slight reduction in the optical Dick effect caused by aliased local oscillator noise. The ultimately limiting technical noise is measured using a technique that does not rely on a second clock or fs-comb.