Comparison of frequency locking of 780 nm diode laser via rubidium saturated absorption and polarization spectroscopies
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摘要: 将激光频率锁定于合适的参考频率,可以有效地抑制激光器的频率起伏。本文采用铷原子D2线超精细跃迁线的饱和吸收光谱和偏振光谱分别获得鉴频曲线,通过电子伺服系统将频率校正信号负反馈到780 nm光栅外腔反馈半导体激光器外腔的压电陶瓷上的方法对激光器进行稳频。介绍了两种方法的基本原理和实验方案。与激光器自由运转300 s时激光器典型的频率起伏约6.6 MHz相比,采用饱和吸收光谱和偏振光谱进行稳频,运转300 s时激光器典型的残余频率起伏分别约为1.5 MHz和0.6 MHz。分析表明,饱和吸收光谱稳频采用了相敏检波技术,需要对激光器进行频率调制,带来了额外的频率噪声,而偏振光谱稳频则是一种完全无频率调制的稳频方案。Abstract: Locking laser frequency to an available reference standard can efficiently suppress the fluctuation of laser frequency and improve the frequency stability. In this paper, the Saturated Absorption Spectroscopy(SAS) and the Polarization Spectroscopy(PS) of rubidium D2 line were used to obtain the frequency discrimination curves. Then the error correcting signals from the frequency discrimination were sent in negatively feedback to the piezeo-electric transducer of a 780 nm external-cavity diode laser(ECDL) by electronic servo-system to realize the laser frequency locking. The basical principles and experimental schemes of two methods were introduced and the experimental results were compared. It shows that the residual fluctuations of laser frequency after being locked by using the two schemes are approximately 1.5 MHz and 0.6 MHz, respectively, compared with that of about 6.6 MHz for the case of ECDL free running. Furthermore, the PS scheme shows better frequency stability than SAS scheme, for SAS brings extra frequency noise by use of the phase sensitive detection which needs to modulate the laser frequency, while PS scheme is completely modulation-free.
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