Hollow Waveguide Multipass Cavity Enhanced Raman Spectroscopy for Trace Gases Sensing

We report a hollow waveguide multipass cavity (HMC) for enhancing the Raman signal of trace gases. Raman signal collection is improved by a hollow waveguide coated with a multilayer dielectric film on the inner surface. The laser beam is reflected 50 times in the HMC, resulting in an extended interaction length between the laser and gases. The variation between the output Raman signal intensity and the HMC parameters is calculated. The reflection behavior of intracavity beams is also simulated to increase the number of beams. The performance of the HMC apparatus is demonstrated by recording the Raman spectra of ambient air, CH₄, and H₂. The limits of detection for CH₄ and H₂ are achieved at 0.87 and 2.06 ppm, respectively, with a total pressure of 0.1 MPa and an exposure time of 60 s. Multigas can be detected with high sensitivity using HMC-enhanced Raman spectroscopy, making it a highly promising approach for gas sensing applications.