Manfred Katherine M, Kirkbride James M R, Ciaffoni Luca, Peverall Robert, Ritchie Grant A D
Opt Lett. 2014 Dec 15;39(24):6811-4. doi: 10.1364/OL.39.006811.
The sensitivity of mid-IR quantum cascade laser (QCL) off-axis cavity-enhanced absorption spectroscopy (CEAS), often limited by cavity mode structure and diffraction losses, was enhanced by applying a broadband RF noise to the laser current. A pump-probe measurement demonstrated that the addition of bandwidth-limited white noise effectively increased the laser linewidth, thereby reducing mode structure associated with CEAS. The broadband noise source offers a more sensitive, more robust alternative to applying single-frequency noise to the laser. Analysis of CEAS measurements of a CO(2) absorption feature at 1890 cm(-1) averaged over 100 ms yielded a minimum detectable absorption of 5.5×10(-3) Hz(-1/2) in the presence of broadband RF perturbation, nearly a tenfold improvement over the unperturbed regime. The short acquisition time makes this technique suitable for breath applications requiring breath-by-breath gas concentration information.
中红外量子级联激光器（QCL）离轴腔增强吸收光谱（CEAS）的灵敏度通常受腔模结构和衍射损耗限制，通过向激光电流施加宽带射频噪声得以提高。泵浦-探测测量表明，添加带宽受限的白噪声有效增加了激光线宽，从而减少了与CEAS相关的模式结构。宽带噪声源为向激光器施加单频噪声提供了一种更灵敏、更稳健的替代方法。对1890 cm⁻¹处CO₂吸收特征的CEAS测量进行100 ms的平均分析，发现在存在宽带射频扰动的情况下，最小可探测吸收为5.5×10⁻³ Hz⁻¹/²，比未受扰动状态提高了近十倍。短采集时间使该技术适用于需要逐次呼吸气体浓度信息的呼吸应用。
