High performance gratings for space applications

Different earth-observation and scientific space missions have the need for special spectrometer gratings. As satellite instruments typically operate close to the technologically accessible limits also the realization of the respective gratings is extremely demanding. Critical parameters are the diffraction efficiency and its polarization dependency, the wavefront error introduced by the grating, stray-light performance, and usability in a space environment. We show that it is necessary to include technological considerations into the design and specification of the grating in order to achieve the optimal performance of the complete optical system. We demonstrate this approach by two examples. The first one is the design and fabrication of the grating for the Radial-Velocity-Spectrometer of the GAIA-mission of the ESA using a novel approach based on an effective medium sub-structure within one grating period. The second example is a high dispersion NIR-spectrometer grating for an earth observation mission. Such gratings are typically realized as immersed structures in order to maximize the dispersion. We show that the same optical performance can be achieved with gratings operating in the resonance domain which can be realized by electron-beam lithography as well