自由空间运转的高功率窄线宽金刚石布里渊激光器研究

Brillouin lasers (BLs) based on waveguide format have obtained extremely narrow linewidth output in the order of sub-Hz, however, the power of those BLs is limited to about microwatt to hundred-milliwatts due to the small beam mode-volume and the low-cascade stimulated Brillouin scattering threshold. Therefore, realizing the free-space operation of BLs becomes an important approach to break through the power bottleneck of current waveguide-based BLs. However, due to the restriction of the properties of currently available Brillouin gain medium and low loss dual resonant frequency locking technology, there has been no report on free-space BLs. In this study, high-fineness Raman cavity and direct-pumped Brillouin oscillator will be applied to realize the free-space operation of BL, combining the diamond as the gain medium that with a high gain coefficient and high thermal conductivity. The methods for improving the efficiency of Brillouin linewidth compression and power conversion will be studied by establishing the steady-state model of free-space BLs and optimizing the parameters of oscillators. The study will lay the foundation for realizing low noise, narrow linewidth and high stability of free space high power BLs, and exploring a high-performance light source for coherent optical communication and laser interference gravitational wave detection.

基于波导型结构的布里渊激光器目前已获得了亚Hz量级的极窄线宽激光输出，但是受光束的小模体积和低级联受激布里渊散射阈值影响，波导型布里渊激光器的功率仅局限在微瓦至百毫瓦量级。因此，实现布里渊激光的自由空间运转成为突破波导型布里渊激光器功率瓶颈的重要途径。然而，受传统布里渊增益介质特性以及难以实现双谐振且低损耗振荡器等因素的制约，一直没有关于自由空间布里渊激光器的报道。本课题利用高精细度拉曼腔和直接泵浦锁频布里渊振荡腔，并以具有高增益系数和极高的热导率的金刚石晶体作为增益介质，实现布里渊激光的自由空间运转。通过建立自由空间布里渊激光器稳态模型和优化振荡器参数，研究提高激光线宽效压缩效率和功率转换效率的方法，为实现低噪声、窄线宽且高稳定性的自由空间高功率布里渊激光输出奠定基础，探索为相干光通信和激光干涉引力波探测提供高性能的光源。

窄线宽激光器在激光干涉引力波探测、精密激光光谱和微波光子学等领域有着重要的应用。近年来，基于受激布里渊散射（SBS）效应的布里渊激光器成为获取低噪声极窄线宽激光输出的重要途径。其中，自由空间谐振器结构在工作波长切换、增益介质的选取以及功率拓展方面具有更高的灵活性，因此在布里渊激光领域具有巨大发展前景。本项目围绕自由空间运转的金刚石布里渊激光器开展了系统的理论和实验研究工作。基于腔共振增强理论和耦合波方程理论建立了自由空间运转布里渊激光器的稳态模型，为自由空间布里渊激光器的实验及参数优化奠定了理论基础。在直接泵浦的布里渊振荡器实验中，实现了1μm波段的功率高达22.5W、线宽为46.9kHz的单频布里渊激光输出。在拉曼作为中间过程的间接产生结构中，利用1μm激光器泵浦金刚石拉曼振荡器，直接获得了中心波长为1.2μm的自由空间级联布里渊激光输出，稳态功率达到百瓦量级。此外，针对1μm波段窄线宽布里渊激光参数测量的问题，搭建了基于短延迟自外差结构的线宽测量装置，并成功地将该方法应用于布里渊激光器的线宽测量，获得了高精度的线宽测量结果。本项目的成果为获得高功率窄线宽的特殊波长布里渊激光辐射提供了新思路和新技术。