Agile cavity ringdown spectroscopy enabled by moderate optical feedback to a quantum cascade laser
通过适度的光学反馈实现量子级联激光器的敏捷腔衰荡光谱
適度な光フィードバックによる量子カスケードレーザの敏捷空洞減衰スペクトルの実現
적당한 광학 피드백을 통해 양자급 레이저의 민첩강 쇠퇴 스펙트럼을 실현하다
Espectro de anillo de cavidad ágil de láseres cuánticos en cascada a través de una retroalimentación óptica moderada
Spectre d'atténuation de cavité agile pour les lasers à cascade quantique par rétroaction optique modérée
Гибкий спектр затухания полости квантового каскадного лазера с умеренной оптической обратной связью
Qinxue Nie ¹, Yibo Peng ², Qiheng Chen ¹, Ningwu Liu ¹, Zhen Wang ¹, Cheng Wang 王成 ², Wei Ren 任伟 ¹
¹ Department of Mechanical and Automation Engineering, The Chinese University of Hong Kong, Hong Kong SAR 999077, China
中国 香港 香港中文大学 机械与自动化工程学
² School of Information Science and Technology, ShanghaiTech University, Shanghai 201210, China
中国 上海 上海科技大学 信息科学与技术学院
Cavity ringdown spectroscopy (CRDS), relying on measuring the decay time of photons inside a high-finesse optical cavity, offers an important analytical tool for chemistry, physics, environmental science, and biology. Through the reflection of a slight amount of phase-coherent light back to the laser source, the resonant optical feedback approach effectively couples the laser beam into the optical cavity and achieves a high signal-to-noise ratio.
However, the need for active phase-locking mechanisms complicates the spectroscopic system, limiting its primarily laboratory-based use. Here, we report how passive optical feedback can be implemented in a quantum cascade laser (QCL) based CRDS system to address this issue. Without using any phase-locking loops, we reflect a moderate amount of light (–18.2 dB) to a continuous-wave QCL simply using a fixed flat mirror, narrowing the QCL linewidth from 1.2 MHz to 170 kHz and significantly increasing the laser-cavity coupling efficiency.
To validate the method’s feasibility and effectiveness, we measured the absorption line (P(18e), 2207.62 cm−1) of N2O in a Fabry–Perot cavity with a high finesse of ~52000 and an inter-mirror distance of 33 cm. This agile approach paves the way for revolutionizing existing analytical tools by offering compact and high-fidelity mid-infrared CRDS systems.
