Full-Power Optical Feedback Fabry–Perot Cavity-Enhanced Raman Spectroscopy for Detecting SF ₆ Decomposition Characteristic Gases

Accurate detection and analysis of characteristic gases during SF₆ decomposition are crucial for improving the operational reliability of SF₆ gas-insulated equipment. In this paper, a full-power optical feedback frequency-locking technique is proposed, in which the optical heterodyne approach is utilized to achieve frequency locking. This approach overcomes the 50% duty cycle limitation of conventional optical feedback techniques and increases the cavity mode signal duty cycle to 100%. The technique is further applied to lock a Fabry-Perot (F-P) cavity in the visible wavelength band, establishing a full-power optical feedback frequency-locking F-P cavity-enhanced Raman spectroscopy gas detection platform with a laser power gain of 688 times. In addition, detection of characteristic gases generated during SF₆ decomposition is achieved. Using standard mixed gas samples, the Raman peak positions for qualitative and quantitative analysis of these gases are determined, along with detection limits at the μL/L level (SF₆: 5.83 μL/L, CO: 19.21 μL/L, CO₂: 6.44 μL/L, COS: 2.28 μL/L, SO₂: 2.74 μL/L, CF₄: 5.65 μL/L, SOF₂: 4.60 μL/L, SO₂F₂: 4.15 μL/L). This research provides a foundation for achieving high-sensitivity Raman spectroscopy online monitoring of characteristic gases released during SF₆ decomposition, while simultaneously advancing the development of full-power optical feedback frequency-locked trace gas detection technology.