length Mid-infrared absorption spectroscopy of ethylene at 10.5 μm using a chalcogenide hollow-core antiresonant fiber

We demonstrate the mid-infrared absorption spectroscopy with a chalcogenide glass IG3 hollow-core anti -resonant fiber (HC-ARF) for gas sensing at 10.5 mu m. A continuous-wave quantum cascade laser (CW-QCL) is adopted to detect the strong absorption line of ethylene (C2H4) centered at 949.5 cm-1 by coupling the laser beam into a chalcogenide HC-ARF of 22 cm in length. Both direct absorption spectroscopy (DAS) and wavelength modulation spectroscopy (WMS) are performed in this study for comparison. At the integration time of 0.1 s, the noise equivalent absorption (NEA) coefficient is determined to be 4.7 x 10-5 cm-1 for DAS and 5.1 x 10-6 cm- 1 for WMS, respectively. Based on the Allan-Werle deviation analysis, the NEA coefficient of WMS can be further improved to 4.0 x 10-7 cm-1 by using a longer integration time of 80 s. The combination of QCLs and chalco-genide glass HC-ARFs provides a promising platform for mid-infrared gas sensing applications.