A comprehensive metrological framework for performance evaluation of an ultra-stable cavity-laser system

Ultra-low expansion optical cavity is a critical component for generating lasers with excellent performances. The comprehensive performance of such a system is governed by a suite of parameters, including the free spectral range (FSR), finesse, zero-crossing temperature (ZCT), laser linewidth, and phase noise. In this study, we implement an integrated metrological framework to characterize these key parameters of a homemade cavity-laser system with high precision. In particular, we determine the FSR via a radio frequency modulation sideband technique, optimized for enhancing measurement accuracy. The finesse is measured by cavity ring-down spectroscopy. Notably, the ZCT is identified through a scanning confocal Fabry–Pérot interferometry referenced to a stabilized He–Ne laser, which eliminates the need for optical beat-note detection and offers broader wavelength applicability. Furthermore, laser linewidth is quantified via short-delay self-heterodyne interferometry and its phase noise is extracted from the same setup. Our measurements yield precise results: an FSR of 1496.8867(3) MHz, a finesse of 89350(380), a ZCT of 56.96(17) °C, and a narrowed linewidth of 229(28) Hz. This work establishes a systematic toolkit for the characteristic assessment of ultra-stable cavity-laser systems.