Detection of C2H2 and HCl using mid-infrared degenerate four-wave mixing with stable beam alignment: towards practical in situ sensing of trace molecular species

摘要: A stable and convenient optical system to realize the forward phase-matching geometry for degenerate four-wave mixing (DFWM) is demonstrated in mid-infrared spectral region by measuring DFWM signals generated acetylene (C2H2) hydrogen chloride (HCl) molecules probing fundamental ro-vibrational transitions. IR laser pulses tunable from 2900 cm−1 3350 with a 0.025 linewidth were obtained using composed of an injection seeded Nd:YAG laser, dye frequency unit. At room temperature atmospheric pressure, detection limit 35 ppm (∼ 9.5×1014 molecules/cm3) C2H2 was achieved gas flow C2H2/N2 mixture scanning P(11) line (010(11)0)–(0000000) band. The HCl molecule measured be 25 (∼6.8×1014 same environment R(4) line. dependences signal intensities on molecular concentrations pulse energies as target species. variations shapes changes buffer pressures recorded analyzed. experimental setup this work facilitates practical implementation situ, sensitive species sensing species-specific, spatial temporal resolution 2.7–3.3 μm (3000–3700 cm−1), where various important combustion have absorption bands.