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arXiv 1408.2829astro-ph.IM
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Subaru Prime Focus摄谱仪的体相位全息光栅:原型光栅装置的性能测量

Volume phase holographic gratings for the Subaru Prime Focus Spectrograph: performance measurements of the prototype grating set

Robert Barkhouser, James Arns, James E. Gunn

摘要:

主焦点摄谱仪(PFS)是为8.2米斯巴鲁望远镜开发的主要仪器。四个相同的摄谱仪模块位于一个Nasmyth焦点上方的房间里。一条55米长的光纤电缆将光从主焦点的机器人定位器传输到光谱仪,位于为Hyper Suprime-Cam开发的宽视场校正器后面。该定位器包含2400根光纤,覆盖1.3度六边形视场。摄谱仪的光学设计包括施密特准直器,两个二向色分束器将光分成三个通道,每个通道有一个体积相位全息(VPH)光栅和一个双校正器,改进的施密特再成像相机。该设计提供了275 mm的准直光束直径,从380 nm到1.26 \textmu m的宽同时波长覆盖范围,以及相机所需的快速f/1.05焦比下的良好成像性能,以避免对光纤的过采样。三个通道被指定为蓝色、红色和近红外(NIR),并且覆盖带通380- 650 nm(蓝色)、630- 970 nm(红色)和0.94- 1.26 \textmu m(NIR)。两个Hamamatsu 2k $\times$ 4k,15 μ \textmu m像素CCD的拼接记录了蓝色和红色通道中的光谱,而NIR通道采用来自Teledyne的4k $\times$ 4k,去除衬底的HAWAII-4 RG阵列,具有15 μ \textmu m像素和1.7 μ \textmu m波长截止。VPH光栅是PFS的一个明显选择,一套三个原型VPH光栅(蓝色,红色和近红外设计各一个)已被订购,并已于最近交付。在本文中,我们提出了PFS光栅的设计和规格,用于测试原型和最终光栅的计划和设置,以及最近的原型光栅组的光学测试结果。

英文摘要:

The Prime Focus Spectrograph (PFS) is a major instrument under development for the 8.2 m Subaru telescope. Four identical spectrograph modules are located in a room above one Nasmyth focus. A 55~m fiber optic cable feeds light to the spectrographs from a robotic positioner at the prime focus, behind the wide-field corrector developed for Hyper Suprime-Cam. The positioner contains 2400 fibers and covers a 1.3~degree hexagonal field of view. The spectrograph optical design consists of a Schmidt collimator, two dichroic beamsplitters to split the light into three channels, and for each channel a volume phase holographic (VPH) grating and a dual-corrector, modified Schmidt reimaging camera. This design provides a 275~mm collimated beam diameter, wide simultaneous wavelength coverage from 380~nm to 1.26~\textmu m, and good imaging performance at the fast f/1.05 focal ratio required from the cameras to avoid oversampling the fibers. The three channels are designated as the blue, red, and near-infrared (NIR), and cover the bandpasses 380--650~nm (blue), 630--970~nm (red), and 0.94--1.26~\textmu m (NIR). A mosaic of two Hamamatsu 2k$\times$4k, 15~\textmu m pixel CCDs records the spectra in the blue and red channels, while the NIR channel employs a 4k$\times$4k, substrate-removed HAWAII-4RG array from Teledyne, with 15~\textmu m pixels and a 1.7~\textmu m wavelength cutoff. VPH gratings were an obvious choice for PFS and a set of three prototype VPH gratings (one each of the blue, red, and NIR designs) was ordered and has been recently delivered. In this paper we present the design and specifications for the PFS gratings, the plan and setups used for testing both the prototype and final gratings, and results from recent optical testing of the prototype grating set.

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