Optical-Feedback Cavity-Enhanced Raman Spectroscopy with Continuous Laser-to-Cavity Locking for Multigas Detection

A multigas detection technology based on optical-feedback cavity-enhanced Raman spectroscopy is introduced. The apparatus combines optical feedback technology with modulation/demodulation technology to realize unintermittent and precise frequency locking of a continuous-wave diode laser at 637 nm, operating at moderate emitting power, to a high-finesse V-shaped optical cavity. This configuration yields a stable intracavity power gain of 1700 times, with an intracavity laser power reaching up to 120 W. Using this apparatus, Raman spectra of multiple gases, including CO₂, CO, H₂, CH₄, C₂H₂, C₂H₄, and C₂H₆, were detected. A comparison of different detection schemes, using forward or 90° direction Raman light collection, was conducted. The results indicate forward detection obtains higher sensitivity, albeit with a larger variable baseline. For most gases, limits of detection (LOD) in parts per million (ppm) were achieved. This method paves the way for the construction of a compact, cost-effective, and sensitive spectrometer for multigas detection.