The influence factors and optimization of modulation transfer spectroscopy for laser frequency discrimination
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摘要:
采用电光位相调制器对泵浦光进行位相调制,得到射频调制转移光谱 (MTS),并研究MTS光谱的类色散信号中心过零点斜率优化问题。通过改变泵浦光的调制频率,泵浦光与探测光的光斑大小,研究MTS光谱信号过零点斜率与二者之间的参数依赖关系,在泵浦光调制频率为~3.6 MHz(大约是自然线宽的0.69倍)时,得到最佳的MTS光谱信号。最后利用最优的MTS光谱将DL Pro @ 852 nm 激光频率锁定到铯原子D2线(F = 4) − (F = 5’)循环跃迁,在60 min采样时间内激光频率起伏约为170 kHz,与自由运转时激光器~11 MHz的频率起伏相比,频率起伏得到了显著改善。
Abstract:We use an electro-optical potential phase modulator to modulate the pump light to obtain radio frequency modulation transfer spectroscopy (MTS), and study the optimization problem of the zero-crossing slope of the center of the dispersive signal of the MTS spectrum. By changing the modulation frequency of the pump light, the spot size of the pump light and the probe light, we study the parameter dependence between the zero-crossing slope of the MTS spectral signal and the modulation frequency, and spot size. The optimal MTS spectral signal is obtained when the pump light modulation frequency is −3.6 MHz (about 0.69 times the natural linewidth). Finally, by using the optimal MTS spectrum, the DL Pro @ 852 nm laser frequency is locked to the cesium atom D2 line (F = 4) - (F = 5') cycle transition, and the laser frequency fluctuation is about 170 kHz in the 60 minutes sampling time, which is significantly improved compared with the frequency fluctuation of the laser −11 MHz during free running.
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图 1 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,
$\omega_{\mathrm{m}} $ 为调制频率,$\omega_{\mathrm{c}} $ 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Figure 1. Diagram of experimental setup. (a) Cesium atomic gas chamber saturation absorption spectrometer; (b) Cesium atomic gas chamber modulation transfer spectrometer.
$ {\omega }_{m} $ is the modulation frequency, and$ {\omega }_{c} $ is the frequency of pump light. The upper and lower sidebands are at frequencies with$ {\omega }_{c}+{\omega }_{m} $ and$ {\omega }_{c}-{\omega }_{m} $ . 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图 4 (a)调制频率、光斑大小对Cs原子D2线(F=4) - (F=5’)循环跃迁的调制转移光谱线宽的影响;(b)探测光与泵浦光光斑大小对Cs原子D2线(F=4) - (F=5’)循环跃迁的调制转移光谱过零点斜率的影响
Figure 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
图 5 (a) Cs原子多普勒展宽的吸收光谱及其微分信号以及带多普勒背景的饱和吸收光谱。(b) DL Pro @ 852 nm光栅外腔半导体激光器自由运转时的典型频率起伏
Figure 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
图 6 (a)调制频率为3.6 MHz时对激光器进行MTS锁频后的典型残余频率起伏;(b)不同调制频率下对激光器进行MTS锁频后的典型残余频率起伏
Figure 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
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