Stability of a high-finesse optical cavity at 493 nm in vacuum for cavity QED with Barium ions

TL;DR

This study investigates the stability of a high-finesse optical cavity at 493 nm in vacuum for cavity QED with Barium ions, focusing on mirror degradation mechanisms and mitigation methods.

Contribution

It provides new insights into vacuum and laser-induced mirror degradation at UV wavelengths and demonstrates potential reversal techniques for cavity deterioration.

Findings

Degradation occurs after long exposure to high circulating powers

Laser-induced deposition is identified as the likely degradation cause

Reversal methods can mitigate cavity loss increases

Abstract

We explore the stability of a high-finesse optical cavity at 493 nm in vacuum for cavity QED with Barium ions. A high-finesse Fabry-Perot cavity is built using mirrors with high-reflectivity (HR) coatings that are implemented by stacking multiple thin films of low-loss dielectrics on substrates. Applications of such HR mirrors in the near ultraviolet (UV) range have been hampered by degradation of coatings in vacuum. Here, we explore the degradation of mirrors with HR coatings at 493 nm in vacuum. We study both vacuum-induced and laser-induced effects on oxide-coated cavity mirrors by probing changes in cavity loss using cavity lifetime measurements. We investigate the role of circulating power in the rate of increase in cavity loss and demonstrate methods of reversal of cavity degradation. While we observe no degradation without long exposure or with short exposures at lower circulating powers, we find evidence of degradation on long exposure to high circulating powers. We discuss potential causes and conclude that laser-induced deposition is the likely cause while ruling out thermally activated processes due to laser-induced heating.