A Custom-Built High-Finesse Reference Cavity for Cold Rydberg Atom Excitation

We present a self-assembled ultra-low expansion (ULE) cavity system designed for high-precision laser frequency stabilization. The cavity mirrors are bonded to the ULE spacer using a low thermal expansion adhesive, and the assembled cavity exhibits a finesse of nearly \(3 \times 10^{4}\). A custom-designed multilayer aluminum housing was developed to passively isolate the cavity from environmental fluctuations. Long-term performance characterization reveals a frequency drift of approximately 164 kHz per day.After locking a diode laser to the cavity using the Pound-Drever-Hall technique, we achieve a linewidth of approximately \(19.4 \text{kHz}\) and a fractional frequency stability of\(6.4 \times 10^{-13}\) at 1 s.To validate the reliability of this frequency-stabilized laser system, we applied it to Rydberg excitation spectroscopy via trap-loss measurements of cold \(^{87}\)Rb atoms. Compared to conventional wavelength meter locking, the cavity-stabilized system significantly improves spectral resolution, reducing the linewidth of the trap-loss spectrum from 34 MHz to 6 MHz. Our system offers a robust and cost-effective solution for high-resolution spectroscopy, with applications in coherent control of Rydberg atoms.