Fig. 1: Concept illustration.
a Concept for the synthesis of multiple IR spectral lines and its application on PA detection of multiple gases. λP1…λPn refer to the wavelengths of pump lines, λ1R1…λ1Rn refer to the wavelengths of Raman laser lines output from the 1st gas-filled ARHCF, λ2R1…λ2Rn refer to the wavelengths of Raman laser lines output from the 2nd gas-filled ARHCF. ARHCF: anti-resonant hollow-core fiber. PA: photoacoustic. b Wavelength conversion examples through filling different gas (CH4, CO2 and N2) into the 1st stage ARHCF. The 2nd stage ARHCF is constantly filled with H2 at 30 bar. Left axis shows measured optical spectra including pump lines, and Raman lines output from the H2-filled 2nd stage ARHCF. Right axis shows the absorbance spectra of CO2 and SO2 obtained from the high-resolution transmission molecular absorption database (HITRAN). The absorbance spectra of CO2 and SO2 are used to show that their absorption peaks are aligned with the two mid-IR spectral lines being synthesized with the proposed concept, therefore constituting the foundation of real-time detection of both CO2 and SO2. Details regarding the measured spectra in b are explained in Supplementary Note 1.
