Three mirror off axis integrated cavity output spectroscopy for the detection of ethylene using a quantum cascade laser

We demonstrate the performance of a compact and robust gas sensor based on a pulsed distributed feedback quantum cascade laser (QCL, laser pulses 30 ns, repetition rate 1 MHz) in combination with off-axis integrated cavity output spectroscopy (OA-ICOS) in an improved 3 mirror configuration. The room temperature laser (wavelength 915 cm−1) was wavelength tuned over ∼0.25 cm−1 with a 4 kHz repetition frequency. A detection limit of 10 ppbv (part-per-billion volume) for regular OA-ICOS is demonstrated for ethylene in 2 min averaging time, which is equal to a noise equivalent absorption sensitivity (NEAS) of 1 × 10−8 cm−1 Hz−1/2. An improved three mirror configuration OA-ICOS scheme showed a four times increase in sensitivity as compared to standard OA-ICOS, resulting in a NEAS of 2.5 × 10−9 cm−1 Hz−1/2. The sensor was used for ethylene detection from apples, stored under controlled atmosphere conditions.