Fast rate dual-comb spectrometer in the water-transparent 7.5–11.5 µm region

We introduce a dual-comb spectrometer based on erbium fiber oscillators at 250 MHz that operates in the 7.5–11.5 µm spectral range over optical bandwidths up to 9 THz with a multi-kHz acquisition rate. Over an observation bandwidth of 0.8 THz, the signal-to-noise ratio per spectral point reaches 168 Hz^0.5 at an acquisition rate of 26 kHz, which allows the investigation of transient processes in the gas phase at high temporal resolution. The system also represents an attractive solution for multi-species atmospheric gas detection in open paths due to the water transparency of the spectral window, the use of thermo-electrically cooled detectors, and the out-of-loop phase correction of the interferograms.