超稳定激光器的$10^{-7}$级别的剩余幅度调制
Residual amplitude modulation at the $10^{-7}$ level for ultra-stable lasers
摘要：
利用Pound-Drever-Hall（PDH）技术在超稳光学腔中稳定激光器是一种广泛应用的方法。PDH方法依赖于激光的相位调制，这通常由电光调制器（EOM）执行。当接近$10^{-16}$水平时，该技术需要对由EOM产生的残余幅度调制（RAM）进行主动控制，以便将激光器的频率稳定性降低到超稳定腔的热噪声极限。在这篇文章中，我们报告的RAM减少的基础上的自由空间EOM，这是用来执行PDH稳定的激光器上的低温硅腔的主动系统的发展。通过采用稳定EOM DC电场、晶体温度和激光功率的数字伺服来获得$1.4 \times 10^{-7}$的RAM稳定性。考虑具有$2.5\times 10^5$精细度的超稳定腔，该RAM水平将在约$5\times 10^{-19}$的水平下对分数频率不稳定性做出贡献，远低于几个$ 10^{-17}$的现有技术热噪声极限。
英文摘要：
The stabilization of lasers on ultra-stable optical cavities by the Pound-Drever-Hall (PDH) technique is a widely used method. The PDH method relies on the phase-modulation of the laser, which is usually performed by an electro-optic modulator (EOM). When approaching the $10^{-16}$ level, this technology requires an active control of the residual amplitude modulation (RAM) generated by the EOM in order to bring the frequency stability of the laser down to the thermal noise limit of the ultra-stable cavity. In this article, we report on the development of an active system of RAM reduction based on a free space EOM, which is used to perform PDH-stabilization of a laser on a cryogenic silicon cavity. A RAM stability of $1.4 \times 10^{-7}$ is obtained by employing a digital servo that stabilizes the EOM DC electric field, the crystal temperature and the laser power. Considering an ultra-stable cavity with a finesse of $2.5\times 10^5$, this RAM level would contribute to the fractional frequency instability at the level of about $5\times 10^{-19}$, well below the state of the art thermal noise limit of a few $ 10^{-17}$.
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