Development of EXo-Zodiacal Infrared Telescope (EXZIT) for observation of visible and near-infrared extragalactic background light
Development of EXo-Zodiacal Infrared Telescope (EXZIT) for observation of visible and near-infrared extragalactic background light
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DOI：
10.1117/12.2559169
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发表时间：
2020-12
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通讯作者：
K. Sano;S. Matsuura;K. Tsumura;A. Takahashi;R. Hashimoto;Sota Ogura;Kazuma Yomo;Hikoma Yasutake;Yuta Ino;Reina Tanaka
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作者：
K. Sano;S. Matsuura;K. Tsumura;A. Takahashi;R. Hashimoto;Sota Ogura;Kazuma Yomo;Hikoma Yasutake;Yuta Ino;Reina Tanaka
河外背景光（EBL）由整个宇宙历史中发射的全部辐射组成，是研究早期宇宙天体物理学的一个重要观测量，如第一颗恒星或原始黑洞。在可见光和近红外波段，黄道光（ZL）是太阳光被行星际尘埃散射后的最亮前景，它的不确定性限制了EBL测量的准确性。为了克服这个问题，从日心距离超过5 Au，ZL是可以忽略不计的观测，是有希望的。为了实现在深空的EBL观测，我们一直在开发太阳帆航天器上的EXO-黄道红外望远镜（EXZIT），计划于2030年左右在日本进行木星特洛伊。根据我们的使命研究，三反射镜反射式望远镜光学设计具有90 mm × 50 mm的有效孔径和16 deg × 8 deg的视场（FoV），随后是焦平面阵列夏威夷-2 RG，具有线性可变滤波器，可以检测0.4-1.6 μm的高显著性EBL，特定波长分辨率为1.20 μm。在本研究中，我们开发了测试光学器件来展示室温下的光学性能，以供未来观察。通过采用非球面反射镜，设计了像差最小的光学系统，使焦平面上的点扩散函数（PSF）约为3 pix × 3 pix。反射镜是由加工铝合金A6061与蜂窝处理的背面，以减少反射镜的质量。在将反射镜与支撑夹具集成和对准后，通过插入不同入射角的准直光束，覆盖整个FoV，由可见光相机测量焦平面上的PSF。我们评估的PSF的大小，通过分析包围的能量与预期的光线跟踪模拟的光学比较。在整个光学器件的FoV中，测量的PSF尺寸与模拟相当。本研究证明了非球面镜的精密加工和所设计的光学系统的光学性能。作为下一步，我们计划开发EXZIT的热结构，以证明在低温下的光学性能。
Extragalactic background light (EBL) consists of entire radiation emitted throughout the cosmic history and is one crucial observable quantity to study astrophysics in the early universe, such as first stellar objects or primordial black holes. In the visible and near-infrared, zodiacal light (ZL), sunlight scattered by interplanetary dust, is the brightest foreground for observer in the near-earth orbit and its uncertainty limits accuracy of the EBL measurement. To overcome this problem, observations from heliocentric distance beyond 5 au, where the ZL is negligible, is promising. To achieve the EBL observation in deep space, we have been developing EXo- Zodiacal Infrared Telescope (EXZIT) onboard a solar sail spacecraft to Jovian Trojans planned in Japan around 2030. According to our mission study, a three-mirror reflective telescope optics design with a 90mm × 50mm effective aperture and 16 deg × 8 deg field of view (FoV) followed by a focal plane array HAWAII-2RG with a linear variable filter makes available to detect the EBL at high significance in 0.4–1.6 μm with specific wavelength resolution of ∼ 20 . In the present study, we develop test optics to demonstrate optical performance in room temperature for the future observation. By adopting only mirrors of aspherical surface, we design the optics whose aberration is minimized to show point spread function (PSF) of approximately 3 pix × 3 pix on the focal plane. The mirrors are fabricated by machining aluminum alloy A6061 with a honeycomb processing on the back surface to reduce the mirror mass. After integrating and aligning the mirrors with support jigs, we measure the PSF on the focal plane by a visible camera by inserting collimated beam of different angle of incidence, covering the whole FoV. We evaluate the PSF size by analyzing encircled energy in comparison with that expected from the ray-trace simulation of the optics. Throughout the FoV of the optics, the measured PSF size is comparable to the simulation. The present study demonstrates the precision machining of the aspherical mirrors and the optical performance of the designed optics. As a next step, we plan to develop thermal structure of EXZIT to demonstrate the optical performance in low temperature.