Temperature-compensated ultra-stable optical cavity with re-entrant design.

Ultra-stable optical cavities with adjustable zero-crossing temperatures feature low thermal expansion and low-temperature control power consumption. We develop a re-entrant cavity featuring flexible and nondestructive zero-crossing temperature tuning capabilities, with a tunable range of 49°C. Using the same ultra-low expansion glass (ULE) batch with a zero-crossing temperature of 16.0(4)°C, we experimentally demonstrate a re-entrant cavity with a higher zero-crossing temperature tuning to 24.7(4)°C, significantly increasing the operational range compared to traditional sandwich cavities. The ultra-stable laser system developed on this re-entrant cavity shows a thermal noise limited performance of 1.05(1) × 10^-15 at 0.2 s and a good long-term performance, making it suitable for portable applications such as space-borne laser sources.