Grism and immersion grating for space telescope
Grism and immersion grating for space telescope
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空间望远镜用光栅和浸没光栅
DOI：
10.1117/12.2308014
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发表时间：
2017
期刊：
影响因子：
--
通讯作者：
et al.
中科院分区：
文献类型：
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作者：
Ebizuka Noboru ;Oka Kiko ;Kashiwagi Masako ;Kodate Kashiko ;Wakaki Moriaki ;Morita Shin-ya ;Yin Shaohui ;Omori Hitoshi ;Iye Masanori ;Yamada Akiko ;et al.
棱镜是一种多用途的色散元件，适用于从紫外到红外的天文仪器。在空间应用中使用棱镜代替反射光栅的主要好处是减小了光学系统的尺寸，因为准直器和随后的光学元件可以位于棱镜附近。表面起伏棱镜由透射光栅和棱镜组成，通过调节棱镜顶角，可以使衍射光束沿着直视方向以特定的阶数和波长直接偏转。体相位全息（VPH）棱镜由一个厚的VPH光栅夹在两个棱镜之间，作为特定的阶数和波长对准的直视方向。VPH光栅在高色散应用中具有理想的衍射效率。另一方面，SR光栅可以在较低色散的应用中实现高衍射效率。8.2米斯巴鲁望远镜的弱目标照相机和摄谱仪（FOCAS）的分辨率为250 ~ 3000，其11个光栅中有5个是用复制法制作的SR光栅。FOCAS的六个额外的Grisms具有从3，000到7，000的分辨率是VPH Grisms。本文提出了一种用于宽波长范围高色散光谱仪的“准布拉格光栅”，以锗浸没光栅为例，由于锗的折射率在1.6 ~ 20 μm范围内超过4.0，因此它可以使光谱仪的体积减小到普通反射光栅的1/64。采用电解修整的方法，利用纳米级精密加工设备和铸铁磨杯，成功地制作了中红外高色散光谱仪（IRHS）浸没式光栅原型。
The grism is a versatile dispersion element for an astronomical instrument ranging from ultraviolet to infrared. Major benefit of using a grism in a space application, instead of a reflection grating, is the size reduction of optical system because collimator and following optical elements could locate near by the grism. The surface relief (SR) grism is consisted a transmission grating and a prism, vertex angle of which is adjusted to redirect the diffracted beam straight along the direct vision direction at a specific order and wavelength. The volume phase holographic (VPH) grism consists a thick VPH grating sandwiched between two prisms, as specific order and wavelength is aligned the direct vision direction. The VPH grating inheres ideal diffraction efficiency on a higher dispersion application. On the other hand, the SR grating could achieve high diffraction efficiency on a lower dispersion application. Five grisms among eleven for the Faint Object Camera And Spectrograph (FOCAS) of the 8.2m Subaru Telescope with the resolving power from 250 to 3,000 are SR grisms fabricated by a replication method. Six additional grisms of FOCAS with the resolving power from 3,000 to 7,000 are VPH grisms. We propose “Quasi-Bragg grism” for a high dispersion spectroscopy with wide wavelength range.The germanium immersion grating for instance could reduce 1/64 as the total volume of a spectrograph with a conventional reflection grating since refractive index of germanium is over 4.0 from 1.6 to 20 μm. The prototype immersion gratings for the mid-InfraRed High dispersion Spectrograph (IRHS) are successfully fabricated by a nano-precision machine and grinding cup of cast iron with electrolytic dressing method.