Temperature-insensitive tunable and stable Fabry-Perot cavity for atomic physics

Optical Fabry-Perot cavities are crucial tools for metrology experiments, where they achieve extreme length stability and now can serve as highly proficient references for probing fine atomic transitions. For some atomic physics experiments however, tunability of the system to atomic transitions enables atom-light interactions. Achieving both frequency stability and tunability in a single cavity has remained a challenge, forcing metrology experiments exploiting atom-cavity interactions to rely on external active feedback systems to stabilize the length of the cavity. Here, we describe a piezoelectrically-tunable cavity with a cancellation of the coefficient of thermal expansion at around 5^ 5 ∘ C , achieving a fractional frequency instability of 4× 10⁻¹³ 4 × 10 − 13 level for 1 s integration time. This advance eliminates the need for external stabilization in many atom-cavity experiments, making this design ideal for applications such as ultra-stable superradiant lasers and other cavity quantum electrodynamics experiments.