Avalanche photodiodes (APDs) are a practical option for space-based quantum communications requiring single-photon detection. However, radiation damage to APDs significantly increases their dark count rates and thus reduces their useful lifetimes in orbit. We show that high-power laser annealing of irradiated APDs of three different models (Excelitas C30902SH, Excelitas SLiK, and Laser Components SAP500S2) heals the radiation damage and several APDs are restored to typical pre-radiation dark count rates. Of nine samples we test, six APDs were thermally annealed in a previous experiment as another solution to mitigate the radiation damage. Laser annealing reduces the dark count rates further in all samples with the maximum dark count rate reduction factor varying between 5.3 and 758 when operating at ${-}80^{\circ}\mathrm{C}$ . This indicates that laser annealing is a more effective method than thermal annealing. The illumination power to reach these reduction factors ranges from 0.8 to 1.6 W. Other photon detection characteristics, such as photon detection efficiency, timing jitter, and afterpulsing probability, fluctuate but the overall performance of quantum communications should be largely unaffected by these variations. These results herald a promising method to extend the lifetime of a quantum satellite equipped with APDs.

中文翻译：

---

激光退火可以修复雪崩光电二极管的辐射损伤。

雪崩光电二极管 (APD) 是需要单光子检测的天基量子通信的实用选择。然而，APD 的辐射损伤会显着增加其暗计数率，从而缩短其在轨道上的使用寿命。我们证明，对三种不同型号（Excelitas C30902SH、Excelitas SLiK 和激光组件 SAP500S2）的辐照 APD 进行高功率激光退火可以治愈辐射损伤，并且多个 APD 恢复到典型的辐射前暗计数率。在我们测试的 9 个样品中，有 6 个 APD 在之前的实验中进行了热退火，作为减轻辐射损伤的另一种解决方案。激光退火进一步降低了所有样品的暗计数率，当在 ${-}80^{\circ}\mathrm{C}$ 下运行时，最大暗计数率降低因子在 5.3 到 758 之间变化。这表明激光退火是比热退火更有效的方法。达到这些降低因子的照明功率范围为 0.8 至 1.6 W。其他光子探测特性（例如光子探测效率、定时抖动和后脉冲概率）会发生波动，但量子通信的整体性能应在很大程度上不受这些变化的影响。这些结果预示着一种有前途的方法可以延长配备 APD 的量子卫星的寿命。