基于极高Q值晶体回音壁腔的窄线宽布里渊激光器研究

Narrow linewidth lasers are of great importance for applications such as optical communication, optical sensing and many precision measurements. Compared with traditional fiber lasers, continuous wave Brillouin lasers based on whispering gallery mode resonators can feature small volumes and very low thresholds. Therefore, they provide a new approach for the development of narrow linewidth lasers. To date, the investigation of the Brillouin laser performance focuses on fused silica microresonators. Nevertheless, crystalline resonator can provide a versatile platform for improving the performance of such lasers. In this proposal, we plan to choose different crystals, optimize and design the resonators. We will fabricate the optical cavities with surface roughness less than 1 nm by mechanical polishing. Quality factors above 10^9 in both ultraviolet and near-infrared regimes will also be achieved. By using the temperature stabilization and laser locking techniques, Brillouin lasing with linewidth less than 100 Hz can be realized. Besides, we will use a sub-hertz ultrastable laser as the pump source to study its stimulated Brillouin scattering. By examining the noise of the laser setup, further optimization can be carried out in order to achieve the thermal noise limited laser performance. This project will lay a foundation for the development of new compact narrow linewidth lasers in the future.

窄线宽激光器在光通信、光传感及许多高精密测量领域有着极其重要的作用。相比传统的光纤激光器，基于回音壁模式谐振腔的连续布里渊激光器具有更为紧凑的体积和极低的阈值，因此为获取这种激光器提供了新的途径。目前国际上的相关研究主要针对二氧化硅玻璃光学微腔，而晶体腔能够为提高布里渊激光器的线宽性能提供多样化的平台。本项目拟对晶体腔进行材料选择和优化设计，采用精密研磨抛光法研制表面粗糙度优于1 nm的晶体谐振腔，获得在紫外和近红外波段高于10^9的Q值，通过温控和泵浦光波长的锁定，实现线宽在百赫兹内的连续布里渊激光输出。此外，本项目拟研究以亚赫兹线宽超稳激光作为泵浦源的受激布里渊散射，通过分析实验装置中的噪声，探索能够接近热噪声极限的实验设计。本项目的开展将为下一步研制新一代紧凑型窄线宽激光器打下良好的基础。

窄线宽连续激光器在激光雷达、激光光谱学、激光通讯和遥感等应用领域有着重要的应用前景。紧凑型低噪声激光模块的研制也是前沿研究的热点之一，是需要解决的关键技术。本项目以具备体积小、重量轻及高品质因子特点的单块式全反射腔为研究对象，开展了窄线宽激光器的研制工作。项目研制过程中，我们实现线宽优于2kHz的单块非平面环形腔激光器，对该激光头单元进行了小型模块化封装设计，通过了实验室内部包含振动、冲击和高低温度循环在内的环境模拟摸底试验。同时，我们提出并报道了基于单块非平面环形腔的窄线宽涡旋光激光器，观察到涡旋晶体光束的产生，提出了一种采用平凹透镜作为反射元件的简易拓扑荷数检测技术，系统研究了该类型腔体中涡旋光激光的模式特征和激光性能。通过频率噪声谱测量，我们还发现该激光器在噪声谱高频处具备很低的频率噪声（达0.1Hz/Hz^1/2）。本项目的研究成果结合了单块全反射腔的紧凑性、低噪声性能以及涡旋光束所带有的轨道角动量特征，为进一步拓展该激光器在激光精密测量的应用奠定了技术基础。