EUSO-Balloon is the first balloon pathfinder of the JEM-EUSO (Joint Experiment Missions - Extreme Universe Space Observatory) framework. It is an ultraviolet (UV) telescope designed to test the key technologies and methods necessary for the indirect detection of Ultra High Energy Cosmic Rays (UHECR) by observing from above the fluorescence emission produced by Extensive Air Showers (EAS) in the 290-430 nm band. The instrument was launched on the 24$^{t}^{h}$ of August, 2014 by the French space agency (CNES) from the stratospheric balloon base in Timmins, Canada and performed an 8 hour night time flight. One of the key technologies of EUSO-Balloon is the refractive optical system which consists of two large aspherical Fresnel lenses (≈ 1 m$^{2}$) and aims at focusing the UV light into a detector plane formed by an array of Multi-Anode Photomultiplying tubes. This work presents a description of the optical system, the test bench and methods used to characterize its performance and the global efficiency. The measured performance can be understood through the addition of a semi-empirical diffusion model to the classic ray-tracing model of the optics.

中文翻译：

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EUSO-Balloon 光学元件的性能

EUSO-Balloon 是 JEM-EUSO（联合实验任务 - 极端宇宙空间天文台）框架的第一个气球探路者。它是一种紫外 (UV) 望远镜，旨在通过从上方观察 290-430 中大范围空气阵雨 (EAS) 产生的荧光发射来测试间接探测超高能宇宙射线 (UHECR) 所需的关键技术和方法。纳米波段。该仪器于 2014 年 8 月 24 美元 ^{t}^{h}$ 由法国航天局 (CNES) 从加拿大蒂明斯的平流层气球基地发射，并进行了 8 小时的夜间飞行。EUSO-Balloon 的关键技术之一是折射光学系统，它由两个大型非球面菲涅耳透镜 (≈ 1 m$^{2}$) 组成，旨在将紫外光聚焦到由多个阵列形成的检测器平面中。 -阳极光电倍增管。这项工作介绍了光学系统、测试台和用于表征其性能和全局效率的方法。通过在光学器件的经典光线追踪模型中添加半经验扩散模型，可以理解测量的性能。