Low temperature GRISM direct bonding

For spectroscopy in space, GRISM elements –obtained by patterning gratings on a prism surface – are gaining increasing interest. Originally developed as dispersive elements for insertion into an imaging light path without deflecting the beam, they are progressively found in sophisticated multi stage dispersion optics. We report on GRISM manufacturing by joining the individual functional elements –prisms and gratings – to suitable components. Fused silica was used as glass material and the gratings were realized by e-beam lithography und dry etching. Alignment of the grating dispersion direction to the prism angle was realized by passive adjustment. Materials adapted bonds of high transmission, stiffness and strength were obtained at temperatures of about 200°C in vacuum by hydrophilic direct bonding. Examples for bonding uncoated as well as coated fused silica surfaces are given. The results illustrate the great potential of hydrophilic glass direct bonding for manufacturing transmission optics to be used under highly demanding environmental conditions, as typical in space.