用于Hg原子光晶格钟的低漂移率超稳腔系统

Ultra-Stable Cavity System with Low Drift Rate for Mercury Optical Lattice Clock

光晶格钟需要高稳定度的超稳激光,而超稳激光的频率稳定性受限于超稳腔的热噪声和温度涨落,因此,降低超稳腔的温度涨落对于超稳激光的频率噪声达到热噪声极限具有重要意义。分别从时域和频域上分析了达到热噪声极限对超稳腔温度稳定性的要求,设计了超稳腔控温系统,其包括一层被动隔热、两层主动控温的超稳腔真空系统和主动控温装置;找到了超稳腔的零膨胀工作温度;测量了真空隔热系统的温度传递时间常数(3.6d);监测了真空腔内主动控温层11d的温度涨落(<1mK)。通过实验测量和理论分析,在频域和时域上分别计算得到了超稳腔的温度波动,确定了千秒内的温度涨落引起的频率噪声均在热噪声极限以下。利用磁光阱产生的199 Hg冷原子的钟频跃迁光谱测得超稳腔的长期温度漂移为4.2kHz/d,符合Hg原子光晶格钟的要求。

The ultra-stable laser is a key component in optical lattice clock,whose frequency stability is limited by the thermal noise and affected by the temperature fluctuation of ultra-stable cavity.Thus the temperature fluctuation is a serious obstacle in pursuing thermal-noise-limit of ultra-stable laser.In this paper,we analyze the requirement of the temperature stability to reach the thermal-noise-limit in frequency domain and time domain,and design the thermal-isolation vacuum system（with one passive thermal shield layer and two active temperature stabilized layers）and the corresponding temperature controller.Having developed the ultra-stable cavity system,we measure the zero-expansion work temperature of the ultra-stable cavity,the temperature transferring time constant of the thermal shield（3.6 d）,and the temperature fluctuation of the temperature stabilized layer in vacuum in 11 d（1 mK）.With these data,we calculate the temperature fluctuation of the ultra-stable cavity,and evaluate that the frequency noise induced from the temperature fluctuation which is all below the thermal-noise-limit in 1000 sintegration time.Moreover,we also use the clock transition spectrum of the 199 Hg cold atoms in magneto-optical trap to measure the long-term drift rate of the ultra-stable cavity（4.2 kHz/d）.This frequency drift rate of ultra-stable cavity is competent to mercury optical lattice clock.