Fused silica GRISMs manufactured by hydrophilic direct bonding at moderate heating
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For high-resolution spectroscopy in space, GRISM elements—obtained by patterning gratings onto a prism surface—find increasing applications. We report on GRISM manufacturing by joining the individual functional elements—prisms and gratings—to suitable components by the technology of hydrophilic direct bonding. Fused silica was used as a substrate material and binary gratings were fabricated by standard e-beam lithography and dry etching. Alignment of the grating dispersion direction to the prism angle was realized by passive adjustment on dedicated bonding gear matched to the substrate geometry. Materials adapted bonds of high transmission, stiffness, and strength were obtained after heat treatment at temperatures of about 200 °C in vacuum. Examples for bonding uncoated as well as coated grating surfaces are given. The results illustrate the great potential of hydrophilic glass direct bonding for manufacturing transmission optics to be used in space or other heavy duty applications.
KeywordsGRISM manufacturing Direct bonding Fused silica Binary grating
We gratefully acknowledge valuable assistance in sample preparation and characterization by K. Jorke, K. Kleinbauer, N. Heidler, G. Leibeling, T. Benkenstein and A. Gottwald, as well as generous support by R. Eberhardt and A. Tünnermann. Part of this work was sponsored by BMWI/DLR under contract no. 55EE1204 and ESA Contract No. 4000114780/15/NL/KML. We appreciate fruitful discussions with P. Bartsch, R. Greinacher, M. Erdmann, B. Harnisch, and B. Guldimann in this context.
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