利用模清洁器实现锶光钟的光晶格光源强度噪声的抑制

Suppressing the intensity noiseof a lattice laserfor a Sroptical lattice clock using the mode-cleaner

利用模清洁器过滤高频噪声的特性,对锶原子光钟的光晶格光源—813nm半导体激光器的强度噪声进行抑制。首先对模清洁器腰斑和激光器腰斑之间的匹配透镜参数进行理论计算,通过模式匹配,得到模清洁器的反射信号和透射信号。然后利用pound-drever-hall(PDH)边带稳频技术将模清洁器锁定于激光频率上,由模清洁器透射出的激光强度噪声被抑制。利用一对平衡零拍探测器对经过模清洁器前后的激光器强度噪声进行测量。结果表明,未经过模清洁器的激光强度噪声在分析频率30MHz内无法达到散粒噪声极限,经过模清洁器后,激光强度噪声在约8MHz达到散粒噪声极限。通过强度噪声抑制,可使813nm半导体激光器用于锶冷原子光晶格装载实验,并且减小了光晶格噪声对势阱囚禁冷原子的影响,有利于下一步的钟跃迁谱探测实验。

The intensity noise of the 813 nm diode laser, which is used as the laser resource forthe optical lattice of the strontium(Sr) optical clock,is suppressed by using the mode-cleaner with a characteristic of filtering high frequency noise. For matching the beam waist of the mode-cleaner with that of the 813 nm laser, the parameters of the lens located between these twobeam waists are calculated. Then the reflection and transmission signals are obtained through mode-matching. After introducing the optical feedback to the mode-cleanerwith the technology Pound-Drever-Hall, the mode-cleanercan be locked to the frequency of the diode laser,and the intensity noise of the transmission laser is then suppressed.The intensity noiseswere measured by using a pair of balanced photodiode,and the resultsshow that the intensity noise of 813 nm laser filtered by the mode-cleaner reaches Shot-Noise-Limit(SNL) at^8MHz,whereas the intensity noise of 813 nm laserwithout filtering via the mode-cleaner cannot reach the SNL within the analysis frequencies of 30 MHz. The level of noise suppression allows the 813 nm diode laser to be applied to the confinement of atoms in the optical lattice, and the influence of the optical lattice noise on the cold atoms trapped in the potential well is reduced, being good for probing the signal of the clock transitionin the following experiment.