Trace gas detection using anti-resonant hollow-core fiber Raman spectroscopy based on a multi-stage spatial filtering method

Hollow-core anti-resonant fibers (HC-ARFs) have demonstrated remarkable advantages in gas-phase Raman spectroscopy in recent years. However, the background fluorescence surrounding the Raman signal within the fiber core typically exhibits a ring-like but spatially non-uniform distribution, which often overwhelms weak Raman features of trace gases, thus limiting the detection sensitivity. To address this issue, we propose a Raman spectroscopic gas detection system based on hollow-core anti-resonant fiber (HC-ARF), incorporating a multi-stage spatial filtering strategy tailored to the spatially non-uniform distribution of Raman signals and background noise. To implement this strategy, a custom imaging spectrometer was developed, integrating three cascaded spatial filtering components: radial filtering using an iris diaphragm, longitudinal filtering via a precision slit, and lateral filtering through CCD row-selective integration. Compared to the unfiltered condition, this method suppresses approximately 94% of the spectral background noise and enhances the signal-to-noise ratio (SNR) by a factor of 9.4. The system achieves high-sensitivity detection of ¹³CO₂ and ¹²CO₂ in ambient air, with detection limits reaching 0.07 ppm and 0.64 ppm, respectively. Notably, this system enables accurate identification of trace components without requiring complex gas pretreatment, even under high background gas interference. The proposed method provides a promising solution for field-deployable Raman-based gas sensing using HC-ARFs.