Full-power optical feedback frequency locking: A method for improving spectroscopy detection sensitivity of gases

• Increase the duty cycle of the cavity mode signal in the common optical feedback to 100%. • Obtain a relatively large intracavity power gain. • Low limits of detection (LODs) for gas detection by Raman spectroscopy • The detection system has long-term stability due to the application of a unique locking method. Optical feedback frequency locking technology has shown significant advancements in gas spectroscopy detection. While, the duty cycle for laser power buildup in the resonant cavity is approximately 50% due to the inherent limitations, preventing continuous sustainment of maximum power, which leads to a suboptimal gas detection limit for laser spectroscopy. This paper introduces a full-power optical feedback frequency locking method that utilizes the optical heterodyne approach to achieve frequency locking. The duty cycle of the cavity mode signal is increased to 100% during locking, and the intracavity power at full-power locking is about twice as much as that at normal locking. Raman detection of O 2 , N 2 , and CO 2 in air with 20 μL/L LODs is achieved with small incident laser power and low cavity mirrors’ reflectivity. This novel approach may therefore become a powerful and transformative tool for trace gas detection with optical feedback technology in cavity-enhanced absorption spectroscopy, photoacoustic spectroscopy, and photothermal spectroscopy, etc.