Fig. 1. Diagram of experimental setup. (a) Cesium atomic gas chamber saturation absorption spectrometer; (b) Cesium atomic gas chamber modulation transfer spectrometer. is the modulation frequency, and is the frequency of pump light. The upper and lower sidebands are at frequencies with and . Key to figure: λ/2: half-wave plate; PMF: polarization maintaining fiber; PBS: polarization beam splitter cube; EOPM: polarization-maintaining-fiber pig-tailed electro-optic phase modulator; PZT: piezoelectric tranducer; Amp: amplifier; RF: radio frequency; PID: proportional-integral-differential amplifier实验装置图。(a)铯原子气室饱和吸收光谱仪；(b)铯原子气室调制转移光谱仪。图1中，为调制频率，是泵浦光频率，PMF为保偏光纤，PBS为偏振分束棱镜，EOPM为带输入输出单模保偏光纤的电光位相调制器，AMP为放大器，RF为射频，PID为比例-积分-差分放大器

Fig. 2. The cesium saturated absorption spectroscopy (SAS) and the cesium modulation transfer spectroscopy (MTS) with a phase modulation frequency of 3.6 MHz

Fig. 3. (a) Modulation transfer spectral signal and (b) the slope of the zero-crossing point of the modulation transfer spectral signal of cesium (F=4) - (F=5’) cycling transition in D2 line at various modulation frequencies

Fig. 4. (a) Effects of modulation frequency and spot size on the MTS linewidth of cesium (F=4) - (F=5’) cycling transition in D2 line; (b) influence of probe and pump beam sizes on the MTS slope of cesium (F=4) - (F=5’) cycling transition in D2 line

Fig. 5. (a) Cs atomic Doppler broaden absorption spectrum and its first order differential spectrum, and the saturated absorption spectrum with Doppler background. (b) Typical frequency fluctuation of DL Pro @ 852 nm in the free running case

Fig. 6. (a) Typical residual frequency fluctuations after MTS lock of the laser at a phase modulation frequency of 3.6 MHz; (b) typical residual frequency fluctuations after MTS lock of the laser at various phase modulation frequencies