基于频率调制相位优化的激光稳频及其腔衰荡光谱应用OA

Laser-frequency drift and excessive linewidth limit rapid,cost-effective single-point measure-ments in cavity ring-down spectroscopy(CRDS).This work investigates the relationship between modu-lation frequency and demodulation-phase selection in frequency-modulation spectroscopy(FMS)and ap-plies it to laser-frequency stabilization for acetylene CRDS.The modulation-frequency dependence of ab-sorption-and dispersion-phase error signals was analyzed theoretically.The analysis identified an approxi-mately 300 MHz crossover:the absorption phase dominated below 300 MHz,whereas the dispersion phase provided a larger error signal at higher modulation frequencies.An FPGA-based frequency-stabiliza-tion system was developed,and the measured peak-to-peak error-signal variation agreed closely with the theoretical prediction.After optimizing gas pressure and concentration,a proportional-integral-derivative controller locked the laser to the center of the acetylene absorption line,thereby improving frequency sta-bility and reducing the effective linewidth.The stabilized laser was then evaluated in CRDS measure-ments.Allan-variance analysis yielded detection limits of 6.23×10-10 cm-1 at 9 MHz in the absorption phase and 2.51×10-10 cm-1 at 350 MHz in the dispersion phase,compared with 1.55×10-9 cm-1 without stabilization.These values correspond to improvements by factors of 2.49 and 6.18,respectively.Al-though high-frequency dispersion-phase detection achieved the lower detection limit,its advantage should be balanced against increased hardware requirements.The approach supports high-precision,low-cost gas monitoring in environmental and industrial sensing applications.