A Wide-Range PDH Frequency-Locking Method for Cavity-Enhanced Raman Detection Based on Fitting Error Signal

The technique of cavity-enhanced Raman spectroscopy (CERS) is important in the field of gas detection. The optical resonator plays a crucial role in the process of cavity enhancement, making it essential to ensure the stability and anti-interference ability of the optical resonator in CERS detection technology. To improve the stability and anti-interference capability of the resonator, we propose a method known as wide-range fitting frequency-locking (WRFFL). By detecting the transmitted power and the system error signal of the Fabry-Perot (F-P) cavity and modeling it with a neural network, a fitting error signal with a wide range and no Trojan operating point is obtained, and the linear dynamic range of the error signal is extended to a maximum of 15 times the original range. Ultimately, a high-stability optical resonator with strong interference resistance is obtained. We conducted locking performance tests on our proposed method in a CERS detection system. The experimental results demonstrate that not only does this method significantly increase the anti-interference ability of the system but also that the locking duration of the resonator reaches 200 min, which is an order of magnitude greater than that of the traditional locking method; the relative stability of the system reaches $3.12\times 10^{-9}$ , greatly increasing the static stability of the system. At the same time, the system demonstrates strong robustness and universality under various environmental disturbances, highlighting the reliability and adaptability of the method across diverse application scenarios.