铯原子nP_(3/2)(n=70—94)里德伯态的紫外单光子激发及量子亏损测量

基于成熟的光纤激光器、光纤放大器及高效激光频率转换技术,我们在实验中研制了一套瓦级输出的窄线宽连续波单频可调谐318.6 nm紫外激光系统,并在室温铯原子气室中实现了6S_(1/2)—nP_(3/2)(n=70—94)单光子跃迁里德伯激发.借助由铯原子6S_(1/2)(F=4)基态、6P_(3/2)(F′=5)激发态和nP_(3/2)(n=70—94)里德伯态构成的V型三能级系统,通过频率锁定于铯原子6S_(1/2)(F=4)—6P_(3/2)(F′=5)超精细跃迁的852.3 nm探测光束的吸收减弱信号获得了里德伯态的信息,并利用高精度波长计测量了铯原子nP_(3/2)(n=70—94)里德伯态的量子亏损值.经过与理论计算值的变化趋势进行对比,我们认为由于原子气室的里德伯屏蔽效应并不能完全屏蔽外部直流电场,铯原子气室内存在残余的直流电场,影响了对里德伯态的量子亏损值的实验测量.利用残余直流电场的Stark效应理论模型及其与有效主量子数n*的依赖关系,对铯原子里德伯态的量子亏损实验测量值进行了修正.修正后的铯原子nP_(3/2)(n=70—94)态量子亏损测量值为3.5591±0.0007,与理论计算值相吻合.

Measurement of quantum defect of cesium nP3/2 (n=70-94) Rydberg states by using ultraviolet single-photon Rydberg excitation

A narrow-linewidth continuous-wave single-frequency tunable 318.6-nm ultraviolet laser system with watt-level output power is developed in our experiment based on well-developed fiber lasers, fiber amplifiers, and efficient laser frequency conversion technique. Cesium 6S_1/2-nP_3/2 (n=70-94) single-photon Rydberg excitation in a room-temperature cesium atomic vapor cell is realized by using our ultraviolet laser system. The single-photon Rydberg excitation signal is obtained via the V-type three-level atomic system which contains 6S_1/2 (F=4) ground state, 6P_3/2 (F=5) excited state and one of nP_3/2 (n=70-94) Rydberg states. When cesium atoms populated on the ground state are partially excited to Rydberg state by the ultraviolet laser, absorption of 852.3-nm probe beam which is locked to 6S_1/2 (F=4)-6P_3/2 (F'=5) hyperfine transition will decrease. In this way, the cesium Rydberg states are detected. The quantum defects for cesium nP_3/2 (n=70-94) Rydberg states are experimentally measured with a high-precision wavemeter. The variation trend of experimentally measured data deviates from that of calculated values. Due to the fact that the cesium vapor cell is positioned in a magnetic shielding tank, the Zeeman effect can be ignored. Considering that the polarizability of Rydberg atoms is proportional to (n*)⁷, in which n* is the effective principal quantum number, the Rydberg screen effect of cesium atomic vapor cell cannot completely protect cesium atoms from being perturbed by an external DC electric field. Therefore the residual DC electric field existing inside the cesium vapor cell will have a significant influence on quantum defect measurement of Rydberg atoms. Using the theoretical model of Stark effect and the relationship between polarizability of Rydberg atoms and the effective principal quantum number n*, the corrected experimental value of quantum defect for cesium nP_3/2 (n=70-94) Rydberg states is found to be~(3.5591 ±0.0007). The corrected experimental value of quantum defect is consistent with the calculation.