ELT-HIRES the high resolution spectrograph for the ELT: optical design studies for the polarimetric unit
ELT-HIRES the high resolution spectrograph for the ELT: optical design studies for the polarimetric unit
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ELT-雇用 ELT 的高分辨率光谱仪：偏振装置的光学设计研究
DOI：
10.1117/12.2312601
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发表时间：
2018
影响因子：
3.2
通讯作者：
M. Riva
中科院分区：
文献类型：
--
作者：
M. Woche;I. di Varano;K. Strassmeier;M. Weber;U. Laux;M. Riva
本文介绍了在雇佣光学系统a阶段研究背景下ELT偏振计的光学设计。众所周知，为了减小仪器偏振和串扰，偏振计在望远镜光程上的最佳位置是旋转对称焦点。在ELT的特殊情况下，这是由M4以下的中间焦点（IF）表示的，该焦点不能直接接近，因此需要重新成像到至少500毫米的安全距离。由于允许的渐晕面积最大为5弧分的限制，这种位置的传递光学单元的设计具有挑战性。我们在本文中重点介绍了两种光学设计解决方案。第一个是部署双卡塞格伦系统来重新成像中频，其中包括偏振光学器件和其他ELT反射镜，将普通和特殊光束重新定向到前端模块（FE）到内斯密斯焦点上。该模块包括天空旋转、大气色散校正（ADC）、两个波段的波长分裂（UBVRI、zYJH）、场稳定和转换到f/20，将光分配到两对光纤束中以馈送给HIRES光谱仪。另一种解决方案考虑基于光纤的紧凑型中频模块，使用带有福斯特棱镜的史瓦西准直器、ADC和分束器来处理两个光谱带。两个偏振光束由瞳孔成像通过四个独立的长光纤发送到光谱仪的光纤连接模块。在那里，我们将输出光纤的f比从f/2.5转换为f/20。
We present the optical design of the ELT polarimeter in the context of the Phase-A study for HIRES. It is well known that in order to reduce the instrumental polarization and cross-talk, the optimal position for a polarimeter along the optical path of a telescope is the rotationally symmetric focus. In the particular case of ELT this is represented by the intermediate focus (IF) below M4 which is not directly accessible and needs therefore a reimaging to a safety distance of at least 500 mm. The design of a transfer optics unit for such location is challenging due to the constraint of having an allowed vignetting area of maximum 5 arc min. We focus in our paper on two optical design solutions. The first one is deploying a double Cassegrain system to reimage the IF, which includes the polarization optics and feeds the other ELT mirrors, redirecting the ordinary and extraordinary beams to the front end module (FE) onto the Nasmyth focus. This module comprises components for sky derotation, atmospheric dispersion correction (ADC), wavelength splitting in two bands (UBVRI, zYJH), field stabilization and conversion to f/20, dispatching the light into two pairs of fiber bundles to feed the HIRES spectrograph. The other solution considers a fiber based compact IF module, using a Schwarzschild Collimator with Foster prism, ADC and beam splitters for the two spectral bands. The two polarized beams are sent by pupil imaging through four separate long fibers to the fiber link module of the spectrograph. There we convert the output fiber f ratio from f/2.5 to f/20.