Intracavity quartz-enhanced photoacoustic sensor

We report on a spectroscopic technique named intracavity quartz-enhanced photoacoustic spectroscopy (I-QEPAS) employed for sensitive trace-gas detection in the mid-infrared spectral region. It is based on a combination of QEPAS with a buildup optical cavity. The sensor includes a distributed feedback quantum cascade laser emitting at 4.33 mu m. We achieved a laser optical power buildup factor of similar to 500, which corresponds to an intracavity laser power of similar to 0.75 W. CO2 has been selected as the target molecule for the I-QEPAS demonstration. We achieved a detection sensitivity of 300 parts per trillion for 4 s integration time, corresponding to a noise equivalent absorption coefficient of 1.4 x 10(-8) cm(-1) and a normalized noise-equivalent absorption of 3.2 x 10(-10) W cm(-1) Hz(-1/2). (C) 2014 AIP Publishing LLC.