Trace Gas Research Facility, Molecular, and Laser Physics, Institute for Molecules and Materials, Radboud University, Heyendaalseweg 135, 6525 AJ Nijmegen, The Netherlands.
Sensors (Basel). 2018 Jun 27;18(7):2050. doi: 10.3390/s18072050.
We employed a single-mode, widely tunable (~300 cm) external-cavity quantum cascade laser operating around 8 µm for broadband direct absorption spectroscopy and wavelength modulation spectroscopy where a modulation frequency of 50 kHz was employed with high modulation amplitudes of up to 10 GHz. Using a compact multipass cell, we measured the entire molecular absorption band of acetone at ~7.4 µm with a spectral resolution of ~1 cm. In addition, to demonstrate the high modulation dynamic range of the laser, we performed direct absorption (DAS) and second harmonic wavelength modulation spectroscopy (WMS-2f) of the Q-branch peak of acetone molecular absorption band (HWHM ~10 GHz) near 1365 cm. With WMS-2f, a minimum detection limit of 15 ppbv in less than 10 s is achieved, which yields a noise equivalent absorption sensitivity of 1.9 × 10 cm Hz.
我们采用单模、宽调谐（300cm）外腔量子级联激光器，工作在约 8µm 附近，用于宽带直接吸收光谱和波长调制光谱，其中调制频率为 50kHz，调制幅度高达 10GHz。使用紧凑型多通池，我们在7.4µm 处测量了丙酮的整个分子吸收带，光谱分辨率约为 1cm。此外，为了展示激光的高调制动态范围，我们在 1365cm 附近的丙酮分子吸收带（半峰全宽~10GHz）的 Q 支峰上进行了直接吸收（DAS）和二次谐波波长调制光谱（WMS-2f）。采用 WMS-2f，在不到 10s 的时间内实现了 15ppbv 的最低检测限，这使得噪声等效吸收灵敏度达到 1.9×10cmHz。
