Fig. 1. (a) The related hyperfine energy levels of Cs atoms 6S_1/2-6P_3/2-8S_1/2; (b) schematic diagram of the two-color polarization spectroscopy (TCPS). (a) 与实验相关的铯原子6S_1/2-6P_3/2-8S_1/2超精细能级图; (b)双色偏振光谱原理示意图

Fig. 2. Schematic diagram of experimental setup for the TCPS. Keys to the figure: DL, external-cavity diode laser; OI, optical isolator; SAS, saturated absorption spectroscopy; PID, proportion-integration-differentiation controller; HWP, half-wave plate; QWP, quarter-wave plate; M, mirror; PBS, polarization beam splitter cube; Cs cell, cesium vapor cell; DF, dichroic filter; BD, beam dump; PD, photodiode.实验装置示意图　DL为 852和795 nm光栅外腔反馈半导体激光器, OI 为光隔离器, SAS为饱和吸收光谱装置, PID为比例积分微分放大器, HWP为1/2波片, QWP为1/4波片, M为45°高反镜, PBS为立方偏振分光棱镜, Cs Cell为 25 mm × 50 mm 铯原子泡, DF为双色镜, BD为挡光板, PD为光电探测器

Fig. 3. The TCPS for the co-propagation configuration when the 794.6 nm probe laser is scanned over the whole 6P_3/2→8S_1/2 transition, and the frequency of 852.3 nm pump laser is locked on the 6S_1/2(F = 3)→6P_3/2(F'= 2, 3, 4) transition, respectively. 同向传输实验构型, 852.3 nm抽运光频率锁于6S_1/2(F = 3)→6P_3/2(F′ = 2, 3, 4)时, 794.6 nm激光作为探测光的TCPS

Fig. 4. The TCPS for the counter-propagation configuration when the 794.6 nm probe laser is scanned over the whole 6P_3/2→8S_1/2 transition, and the frequency of 852.3 nm pump laser is locked on the 6S_1/2(F = 3)→6P_3/2(F' = 2, 3, 4) transition, respectively. 反向传输实验构型, 852.3 nm抽运光频率锁于6S_1/2(F = 3)→6P_3/2(F' = 2, 3, 4)时, 794.6 nm激光作为探测光的TCPS

Fig. 5. The TCPS for the co-propagation configuration when the 794.6 nm probe laser is scanned, and the frequency of 852.3 nm pump laser is locked on the 6S_1/2(F = 4)→6P_3/2(F' = 3, 4, 5) transition, respectively. 同向传输实验构型, 852.3 nm抽运光频率锁于6S_1/2(F = 4)→6P_3/2(F' = 3, 4, 5)时, 794.6 nm激光作为探测光的双色偏振光谱

Fig. 6. The TCPS for the counter-propagation configuration when the 794.6 nm probe laser is scanned, and the frequency of 852.3 nm pump laser is locked on the 6S_1/2(F = 4)→6P_3/2(F' = 3, 4, 5) transition, respectively. 反向传输实验构型, 852.3 nm抽运光频率锁于6S_1/2(F = 4)—6P_3/2(F' = 3, 4, 5)时, 794.6nm激光作为探测光的双色偏振光谱

Fig. 7. The TCPS with opposite phase, (upper TCPS) angle of λ/4 wave plate is set to 131°; (lower TCPS) angle of λ/4 wave plate is set to 180°. 相位相反的双色偏振光谱TCPS, 红色(上) TCPS对应的λ/4波片位置读数为131°, 黑色(下) TCPS对应的λ/4波片位置读数为180°

Fig. 8. The frequency fluctuation of 794.6 nm laser for free-running and locking on in 225 seconds, respectively.794.6 nm激光器自由运转和锁频后的频率起伏