Clees Sean, Barnes Spencer C, Rault Taylor M, Strand Christopher L, Hanson Ronald K
Department of Mechanical Engineering, Stanford University, Stanford, CA 93405, USA.
Sensors (Basel). 2024 Dec 11;24(24):7920. doi: 10.3390/s24247920.
Distributed feedback lasers, which feature rapid wavelength tunability, are not presently available in the yellow and orange spectral regions, impeding spectroscopic studies of short-lived species that absorb light in this range. To meet this need, a rapidly tunable laser system was constructed, characterized, and demonstrated for measurements of the NH radical at 597.4 nm. The system consisted of three main parts: (1) a distributed feedback diode laser operating at 1194.8 nm, (2) a fiber-coupled optical amplifier, and (3) a periodically poled lithium niobate (PPLN) waveguide for second-harmonic generation. A phase-matching optical frequency bandwidth of 118 GHz and a second-harmonic generation efficiency of 109%/W were determined for the PPLN waveguide, and the intensity and wavelength stability of the system were measured. The rapid-tuning capabilities of the laser system were characterized to explore its potential for use in scanned-direct absorption and wavelength modulation spectroscopy experiments. The feasibility of scanned-direct absorption up to a scan rate of 900 kHz and wavelength modulation spectroscopy at modulation frequencies up to 800 kHz were demonstrated. Finally, the system was deployed in a series of shock tube experiments in which the concentration of NH radicals was measured during the decomposition of NH behind reflected shock waves.
具有快速波长可调谐特性的分布反馈激光器目前在黄色和橙色光谱区域尚不可用，这阻碍了对在此范围内吸收光的短寿命物种的光谱研究。为满足这一需求，构建了一个快速可调谐激光系统，对其进行了表征，并展示了该系统用于测量597.4 nm处的NH自由基的能力。该系统由三个主要部分组成：（1）一个工作在1194.8 nm的分布反馈二极管激光器，（2）一个光纤耦合光放大器，以及（3）一个用于二次谐波产生的周期性极化铌酸锂（PPLN）波导。确定了PPLN波导的相位匹配光频率带宽为118 GHz，二次谐波产生效率为109%/W，并测量了系统的强度和波长稳定性。对激光系统的快速调谐能力进行了表征，以探索其在扫描直接吸收和波长调制光谱实验中的应用潜力。展示了扫描直接吸收高达900 kHz的扫描速率以及调制频率高达800 kHz的波长调制光谱的可行性。最后，该系统被应用于一系列激波管实验中，在反射激波后NH分解过程中测量了NH自由基的浓度。
