热控声光调制器的光束指向稳定
Beam pointing stabilization of an acousto-optic modulator with thermal control
摘要：
声光调制器（AOM）产生的衍射光束广泛应用于各种光学实验中，其中一些实验需要高的角度稳定性和光功率的时间调制。通常，在没有射频补偿伺服系统的无源装置中，很难同时实现角度稳定和高功率调制。在这里，我们提出了一种方法来抑制角漂移和指向噪声只有与AOM晶体的热管理。分析了AOM晶体的角漂移与折射率变化的关系，发现角漂移对温度梯度非常敏感，温度梯度会在AOM晶体内部产生折射率梯度。这提醒我们，这种角漂移可以通过仔细地将零温度梯度区域与声光相互作用区的位置重叠来显著抑制。我们实现了一个水冷的设置，并发现AOM的角漂移减少了100倍以上的热瞬态过程中，和角噪声也被抑制到1/3的非冷却的情况下。应该强调的是，这种热控制方法是一种通用的抑制光束在衍射和衍射方向的漂移。用该角漂移温度模型计算了二氧化碲晶体在1064 nm处的折射率热系数为16 $\times$ 10 $^{-6}$ K $^{-1}$，与前人的研究结果一致.这种热控制技术为需要强度斜坡的光学捕获和远程传感提供了潜在的应用。
英文摘要：
Diffraction beams generated by an acousto-optic modulator (AOM) are widely used in various optical experiments, some of which require high angular stability with the temporal modulation of optical power. Usually, it is difficult to realize both angular stability and high-power modulation in a passive setup without a servo system of radio-frequency compensation. Here, we present a method to suppress the angular drift and pointing noise only with the thermal management of the AOM crystal. We analyze the dependence of the angular drift on the refractive index variation, and find that the angular drift is very sensitivity to the temperature gradient which could induce the refractive index gradient inside the AOM crystal. It reminds us such angular drift could be significantly suppressed by carefully overlapping the zero temperature gradient area with the position of the acousto-optic interaction zone. We implement a water-cooling setup, and find that the angular drift of an AOM is reduced over 100 times during the thermal transient, and the angular noise is also suppressed to 1/3 of the non-cooled case. It should be emphasized that this thermal control method is a general to suppress the beam drift in both the diffraction and the perpendicular-to-diffraction directions. The refractive index thermal coefficient of tellurium dioxide crystal at 1064 nm determined by this angular drift-temperature model is 16$\times$10$^{-6}$ K$^{-1}$ consistent with previous studies. This thermal control technique provides potential applications for optical trapping and remote sensoring that demand for intensity ramps.
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