Torrance Joshua S, Sparkes Ben M, Turner Lincoln D, Scholten Robert E
Opt Express. 2016 May 30;24(11):11396-406. doi: 10.1364/OE.24.011396.
We identify several beneficial characteristics of polarization spectroscopy as an absolute atomic reference for frequency stabilization of lasers, and demonstrate sub-kilohertz laser spectral linewidth narrowing using polarization spectroscopy with high-bandwidth feedback. Polarization spectroscopy provides a highly dispersive velocity-selective absolute atomic reference based on frequency-dependent birefringence in an optically pumped atomic gas. The pumping process leads to dominance of the primary closed transition, suppressing closely-spaced subsidiary resonances which reduce the effective capture range for conventional atomic references. The locking signal is based on subtraction of two orthogonal polarization signals, reducing the effect of laser intensity noise to the shot noise limit. We measure noise-limited servo bandwidth comparable to that of a high-finesse optical cavity without the frequency limit or complexity imposed by optical modulation normally associated with high bandwidth laser frequency stabilization. We demonstrate narrowing to 600±100 Hz laser linewidth using the beatnote between two similarly locked external cavity diode lasers.
我们确定了偏振光谱作为激光频率稳定的绝对原子参考的几个有益特性，并展示了使用具有高带宽反馈的偏振光谱将激光光谱线宽缩小到亚千赫兹。偏振光谱基于光泵浦原子气体中与频率相关的双折射，提供了一种高度色散的速度选择性绝对原子参考。泵浦过程导致主要封闭跃迁占主导地位，抑制了紧密间隔的辅助共振，而这些共振会减小传统原子参考的有效捕获范围。锁定信号基于两个正交偏振信号的减法，将激光强度噪声的影响降低到散粒噪声极限。我们测量到的噪声限制伺服带宽与高精细度光学腔相当，且没有通常与高带宽激光频率稳定相关的光学调制所带来的频率限制或复杂性。我们使用两个类似锁定的外腔二极管激光器之间的拍频，展示了将激光线宽缩小到600±100 Hz。
