Improving the resolution of comb-based frequency measurements using a track and hold amplifier

TL;DR

This paper introduces a track-and-hold amplifier technique to enhance the signal-to-noise ratio in comb-based optical frequency measurements, enabling more reliable spectral transfer at ultra-high precision levels.

Contribution

It presents a novel implementation of gated detection using a single-chip track-and-hold amplifier to improve measurement robustness and sensitivity in optical frequency comb applications.

Findings

Achieved 12dB improvement in beatnote signal-to-noise ratio.

Enabled cycle-slip-free spectral purity transfer.

Reduced system sensitivity to power fluctuations.

Abstract

The advent of optical frequency standards with ultimate uncertainties in the low 1x10$^{-18}$ requires femtosecond frequency combs to support a similar level of resolution in the spectral transfer and the computation of optical frequency ratios. The related experimental challenges grow together with the number of optical frequencies to be measured simultaneously, as in many cases the comb's optical power does not allow reliable beatnote counting or tracking in all the spectral regions of interest. Here we describe the use of a track-and-hold amplifier to implement the gated detection, a previously proposed technique for improving the signal-to-noise ratio of the beatnote between a low-power tooth of the frequency comb and a continuous wave laser. We demonstrate a 12dB improvement in the signal-to-noise ratio of beatnotes involving a broadband-spanning optical comb as compared to traditional detection schemes. Our approach enables reliable and cycle-slip-free spectral purity transfer and reduces the system sensitivity to power drops in the comb spectrum. Being based on a single chip, it is robust, versatile and easily embedded in more complex experimental schemes. Keywords: frequency comb, spectral purity transfer, gated detection, track and hold amplifier.