CW DFB RT diode laser based sensor for trace-gas detection of ethane using novel compact multipass gas absorption cell

The development of a continuous wave (CW), thermoelectrically cooled (TEC), distributed feedback (DFB) laser diode based spectroscopic trace-gas sensor for ultra sensitive and selective ethane (C₂H₆) concentration measurements is reported. The sensor platform used tunable laser diode absorption spectroscopy (TDLAS) and wavelength modulation spectroscopy (WMS) as the detection technique. TDLAS was performed with an ultra-compact 57.6 m effective optical path length innovative spherical multipass cell capable of 459 passes between two mirrors separated by 12.5 cm. For an interference free C₂H₆ absorption line located at 2976.8 cm_-1 a 1σ minimum detection limit of 130 pptv with a 1 second lock-in amplifier time constant was achieved.