Windows for the Small-Sized Telescope (SST) Cameras of the Cherenkov Telescope Array (CTA)

伽马射线是来自宇宙的能量最高的光子。它们不会穿过地球大气层，但有可能通过它们在高层大气中产生的微弱的蓝色光，即切伦科夫辐射，从地面探测到它们。英国的一个团队正在建造一种名为切伦科夫望远镜阵列(CTA)的新望远镜系统，以探测这种辐射，从而准确地确定伽马射线来自哪里以及它们的能量是什么。将有两个望远镜阵列，一个在北半球(在拉帕尔马)，一个在南半球(在智利)。这两个阵列都包括不同大小的望远镜，以探测不同能量的伽马射线。南方阵列将包含许多10个小型望远镜(SST)，这些望远镜旨在探测CTA将看到的最高能量和最稀有的伽马射线。英国团队参与了为SST制造摄像头的工作。这些相机需要非常复杂的窗户来执行4项功能：i.保护光探测器(SiPM)不受灰尘和水的影响；ii.作为滤光片，去除夜空背景(在光谱的红色区域)，同时在蓝色/紫外线下提供高透射率；作为大入射角的减反射膜；和。阻止来自SiPM的红外光子从窗口后表面反射出去。这是一个具有挑战性的问题，我们一直在与位于贝辛斯托克的涂层公司TMF合作。他们设计了一种独特的二氧化汞/二氧化硅涂层，满足了所有要求。这笔赠款将用于生产英国摄像机所需的全部50个窗户。

Gamma-rays are the highest energy photons coming from the Universe. They don't pass through the Earth's atmosphere, but it is possible to detect them from the ground via the flashes of faint, blue light which they create in the upper atmosphere, known as Cherenkov radiation. A team in the UK is involved in building a new system of telescopes, called the Cherenkov Telescope Array (CTA), to detect this radiation and hence pinpoint where the gamma-rays come from and what energy they are. There will be two arrays of telescopes, one in the Northern Hemisphere (on La Palma) and one in the South (in Chile). Both arrays include telescopes of different sizes to detect gamma-rays of different energy. The Southern array will contain many 10s of small-sized telescopes (SSTs) which are designed to detect the most energetic and rarest gamma-rays that CTA will see. The UK team is involved in building the cameras for the SSTs. These cameras need very sophisticated windows to perform 4 functions:i. protect the light detectors (SiPMs) from dust and water;ii. act as filter to remove the night-sky background (in the red region of the spectrum) while providing high transmission in the blue/ultraviolet;iii. act as an anti-reflective coating for high angles of incidence; andiv. stop infrared photons from the SiPMs from being reflected off the rear surface of the window.This challenging problem is one on which we have been working with coating company Thin Metal Films (TMF) in Basingstoke. They have designed a unique hafnium dioxide/silicon dioxide coating which fulfils all the requirements. This grant will fund the production of all 50 windows needed for the cameras in the UK.