基于铷原子420 nm蓝光冷却的主动光钟超辐射激光实验方案  

An experimental scheme of active-optical-clock superradiant laser based on blue-light cooling of 87 Rb at 420 nm

作　　者：史田田 关笑蕾 缪健翔 张佳[1] 潘多 庄伟[2] 陈景标[1] SHI Tian-tian;GUAN Xiao-ei;MIAO Jian-xiang;ZHANG Jia;PAN Duo;ZHUANG Wei;CHEN Jing-biao(State Key Laboratory of Advanced Optical Communication Systems and Networks Institute of Quantum Electronics,Department of Electronics,Peking University,Beijing 100871,China;National Institute of Metrology,Beijing 100013,China)

机构地区：[1]北京大学电子学系区域光纤通信网与新型光纤通信系统国家重点实验室,北京100871 [2]中国计量科学研究院,北京100013

出　　处：《时间频率学报》2022年第2期89-94,共6页Journal of Time and Frequency

基　　金：国家自然科学基金资助项目(91436210);中国博士后科学基金资助项目(BX2021020)。

摘　　要：主动光频标对腔长热噪声具有天然的抑制作用,其激光线宽可突破自发辐射决定的Shawlow-Townes线宽极限,原理上可实现极窄的量子极限线宽。为了解决热原子主动光频标碰撞展宽的影响,本文提出了一种基于冷^(87)Rb原子体系实现主动光钟超辐射激光的实验方法,并开展了理论验证。利用四能级量子结构,420 nm激光同时作为冷却光和泵浦光,可以减小泵浦光引入的光频移,同时,相比于^(87)Rb原子795/780 nm冷却,能实现更低的多普勒冷却极限温度。冷^(87)Rb原子团低精细度光学谐振腔的弱反馈下,能够在6S_(1/2)和5P_(1/2)能级间建立粒子布居反转,最终实现线宽为亚赫兹量级、频率取决于量子跃迁频率的1323 nm主动光钟超辐射激光。该激光既可以作为窄线宽本振激光源,也可直接作为光学频率标准使用。Active optical frequency standards have the advantage of suppression on cavity-pulling effect, resulting in a very narrow quantum-limit linewidth smaller than the classical Schawlow-Townes limit.To reduce the collision broadening of active optical frequency standard using thermal atoms as gain media, here, we propose an experimental scheme to realize the active-optical-clock superradiant laser using the cold ^(87)Rb atoms.Based on the four-level quantum structure, the 420 nm laser simultaneously plays the role of the cooling laser and the pumping laser, which reduce the light shift induced by the pumping light.Moreover, compared with the Doppler cooling limit of ^(87)Rb 795/780 nm transition, a lower Doppler temperature can be achieved.The population inversion between the 6S_(1/2) and 5P_(1/2) states is built up owing to the weak optical feedback of low-finesse resonant cavity.Finally, we will realize a 1323 nm active-optical-clock superradiant laser, whose linewidth is at sub-hertz level and frequency depends on the atomic transition.Such a superradiant laser can be used as the narrow-linewidth local oscillator, as well as the optical frequency standard.

关 键 词：主动光频标 超辐射激光 激光冷却 量子极限线宽 

分 类 号：TH714[机械工程—测试计量技术及仪器]