Hollow core fiber-assisted absorption spectroscopy of methane at 3.4 µm.

A laser-based spectrometer exploiting a novel Kagome-type hollow core photonic crystal fiber, which serves as a gas cell is demonstrated. Low attenuation of this silica-based fiber in the 3.4 µm wavelength region enables accessing strong, fundamental transitions of methane, which was used as a target analyte in the presented experiment. With an all-fiber differential frequency generation source combined with wavelength modulation spectroscopy technique detection limit at single parts-per-million by volume level was obtained. These results show potential for developing compact and sensitive Kagome-fiber-based mid-infrared laser spectrometers.