Ultra-stable transportable ultraviolet clock laser using cancellation between photo-thermal and photo-birefringence noise

TL;DR

This paper presents a portable UV laser system with ultra-stability and low acceleration sensitivity, employing noise cancellation techniques to improve performance for quantum clock applications.

Contribution

The authors develop a transportable UV laser with minimized noise through photo-thermal and photo-birefringence cancellation, achieving high stability and low acceleration sensitivity.

Findings

Achieved fractional frequency instability of ~2 x 10^{-16}

Measured acceleration sensitivity below 4(2) x 10^{-12}/(m/s^2)

Implemented noise cancellation to reduce intra-cavity power fluctuation effects

Abstract

Optical clocks require an ultra-stable laser to probe and precisely measure the frequency of the narrow-linewidth clock transition. We introduce a portable ultraviolet (UV) laser system for use in an aluminum quantum logic clock, demonstrating a fractional frequency instability of approximately $\mathrm{mod}\,\sigma_\mathrm{y} = 2 \times 10^{-16}$. The system is based on an ultra-stable cavity with crystalline AlGaAs/GaAs mirror coatings, alongside with a frequency quadrupling system employing two single-pass second harmonic generation (SHG) stages. Its acceleration sensitivity, measured in all three axes, does not exceed $4(2) \times 10^{-12}$/(ms$^{-2}$) and is among the lowest recorded for transportable systems to date. Additionally, partial cancellation between photo-thermal noise and photo-birefringence noise is used to effectively mitigate noise induced by intra-cavity optical power fluctuation at lower Fourier frequencies.