Gaia RVS grating
This image shows the full size demonstrator model of the blazed transmission grating for the Gaia Radial Velocity Spectrometer (RVS). The large dimensions of the grating (20.5 × 15.5 cm), the image performance (wave front error < 8nm RMS) and the high efficiency (>70%) are the main requirements for this grating.
Within the frame of a feasibility study for ESA the Fraunhofer Institut für Optik und Feinmechanik (IOF) in Jena designed, built and tested this grating. The blaze of the grating is realized by a nano texture of a fused silica plate. At sub-wavelength scale (the RVS will observe in the near-infrared between 847-874 nm) the texture is a repeated pattern of discrete block-shaped patches, forming a binary index modulation structure. The blazed grating is therefore a fully monolithic structure with outstanding optical performance and an efficiency of >80%, well above the required 70%.
The grating has 302.11 grooves per mm. Each groove element (unit cell) has 5 patches of binary index modulation elements over a width of 3.31 µm. See the related image in the right-hand menu for an electron microscope image of individual grooves.