Hu Mengyuan, Ren Wei
Opt Lett. 2022 Jun 1;47(11):2899-2902. doi: 10.1364/OL.460042.
Heterodyne phase-sensitive dispersion spectroscopy (HPSDS) provides an agile method for gas detection by measuring the phase of an amplitude modulation signal. However, previous HPSDS gas sensors have shown limited sensitivity. In this work, we report a new, to the best of our knowledge, dispersion spectroscopic technique, named wavelength-modulation heterodyne phase-sensitive dispersion spectroscopy (WM-HPSDS), to improve the detection sensitivity. As a proof-of-principle demonstration, a quantum cascade laser (QCL) at 5.26 µm is used to exploit the absorption line of nitric oxide (NO) in a 35-cm-long hollow-core fiber. In addition to modulating the injection current of the QCL at 1 GHz to generate the three-tone beam, a 10-kHz sinusoidal waveform is superimposed on the laser current to produce an additional wavelength modulation. We achieve a noise-equivalent concentration of 40 ppb NO using WM-HPSDS at an integration time of 90 s, corresponding to a noise-equivalent absorption (NEA) coefficient of 6.9 × 10 cm. Compared with the conventional HPSDS technique, the developed WM-HPSDS improves the sensitivity by a factor of 8.3.
外差相位敏感色散光谱技术（HPSDS）通过测量调幅信号的相位，为气体检测提供了一种灵活的方法。然而，以往的HPSDS气体传感器灵敏度有限。在这项工作中，据我们所知，我们报告了一种新的色散光谱技术，名为波长调制外差相位敏感色散光谱技术（WM-HPSDS），以提高检测灵敏度。作为原理验证演示，使用了一台波长为5.26 µm的量子级联激光器（QCL），来探测一根35厘米长的空芯光纤中一氧化氮（NO）的吸收线。除了以1 GHz的频率调制QCL的注入电流以产生三音光束外，还在激光电流上叠加了一个10 kHz的正弦波形，以产生额外的波长调制。在90秒的积分时间内，使用WM-HPSDS我们实现了40 ppb NO的噪声等效浓度，对应于6.9×10 cm的噪声等效吸收（NEA）系数。与传统的HPSDS技术相比，所开发的WM-HPSDS将灵敏度提高了8.3倍。
