  Photoacoustic spectroscopys (PAS)-based methane (CH4) detectors have garnered
significant attention with various developed systems using near-infrared (NIR)
laser sources, which requires high-energy and narrow-linewidth laser sources to
achieve high-sensitivity and low-concentration gas detection. The anti-resonant
hollow-core fiber (ARHCF) lasers in the NIR and mid-infrared (MIR) spectral
domain show a great potential for spectroscopy and high-resolution gas
detection. In this work, we demonstrate the generation of a frequency-comb-like
Raman laser with high pulse energy spanning from ultraviolet (UV) (328 nm) to
NIR (2065 nm wavelength) based on a hydrogen (H2)-filled 7-ring ARHCF. The
gas-filled ARHCF fiber is pumped with a custom-laser at 1044 nm with ~100
{\mu}J pulse energy and a few nanoseconds duration. Through stimulated Raman
scattering process, we employ the sixth-order Stokes as case example located at
~1650 nm to demonstrate how the developed high-energy and narrow-linewidth
laser source can effectively be used to detect CH4 in the NIR-II region using
the photoacoustic modality. We report the efficient detection of CH4 with
sensitivity as low as ~550 ppb with an integration time of ~40 s. In
conclusion, the main goal of this work is to demonstrate and emphasize the
potential of the gas-filled ARHCF laser technology for compact next-generation
spectroscopy across different spectral regions.
