Development of Ultimate Transmitting Dispersive Grating (Grism)

为实现安装在8.2m斯巴鲁望远镜上的微弱目标相机和摄谱仪FOCAS和自适应光学日冕成像仪CIAO上的高效棱镜（在棱镜上的透射光栅）的研究和开发。首先，建立了一个测量系统，通过衍射光强度分布的FFT来评估光栅的统治形状。这个系统后来被扩展到能够绝对测量衍射光束的效率。采用超精细三维加工系统，在氟树脂红外透射材料上直接刻划沟槽，测试了用于近红外波段的CIAO光栅的制作。用这种方法制备的光栅在近红外波段的衍射效率为65-70%。采用标准复制方法在沉积在玻璃基板上的树脂材料上制备了FOCAS和Trispec的低色散和中色散光栅，显示出80%的衍射效率。FOCAS的高色散光栅和CIAO光谱模式需要高折射率材料制成的光栅。为了在折射率大于1.9的光学材料上产生深沟槽，人们测试了各种方法，但尚未发现有希望的方法。锗光栅有助于使红外高色散光谱仪的尺寸足够小，以节省成本并提高这种仪器的稳定性。本研究表明，实际制造的这种格栅在10微米波长的应用中表现出可接受的性能，但在2微米波长的应用中，表面粗糙度令人担忧。

Research and development of high efficiency prisms (transmitting gratings ruled on prisms) were carried out for implementation at Faint Object Camera And Spectrograph FOCAS and for Coronagraphic Imager with Adaptive Optics CIAO both to be mounted on the 8.2m Subaru telescope.First of all, a measuring system was set up to evaluate the ruling shape of grisms through the FFT of the intensity distribution of diffracted light. This system was then expanded to enable absolute measurement of efficiency in diffracted beams. Fabrication of grisms for CIAO, to be used in the near infrared wavelength, was tested by ruling grooves directly on infrared transmitting material made of fluorine resine using a hyper fine 3D machining system. The grism actually fabricated in this way has shown to give 65-70% diffraction efficiency in the near infrared. Low dispersion and medium dispersion grisms for FOCAS and for Trispec were made by using the standard replicating method on resin material deposited on glass base plates and was shown to give 80% diffraction efficiency.Grisms made of high refractive index material are required for high dispersion grisms of FOCAS and for CIAO spectroscopic modes. Various methods were tested to produce deep grooves on optical material with refractive index larger than 1.9, but no promising method has yet been identified.Germanium grisms are useful in making the size of the high dispersion spectrograph for infrared small enough to save the cost and to enhance the stability of such an instrument. It was shown in this study that such a grism actually manufactured shows acceptable performance in 10 micron wavelength application but the surface roughness is of concern for use at 2 micron wavelength.