Design, manufacturing, and integration of high precise slit assemblies for spectrometer applications

Slit and double slit assemblies are key components for optical spectrometers. The incoming light is diffracted at the slit edges which disperse the light into several wavelengths. Depending on the optical design of the spectrometer, e. g. the size of detector pixels, requirements for the mechanical accuracy of the slits down to the sub-micron range in absolute width and length are common. In addition, a variation of the width along the slits in sub-micron range is required. The needed slit planarity is less than 5 μm in most of the cases. Depending on the required geometrical slit accuracies, the manufacturing of the slits and their integration concept is different. Mechanical parts, machined by single point diamond turning technology, can be used for slit assemblies. Furthermore, lithographic structured slits mounted in ultra-precise manufactured mechanical holders can be built. For the realization of double slit assemblies, laser structuring of metal foils or lithographic structuring of silicon wafers are used. In most cases, the combination of high precision mechanical manufacturing technologies and non-mechanical lithographic structuring is necessary. The paper describes different design concepts of slit structuring. The mechanical designs of slit assemblies are illustrated, including the manufacturing, assembly and alignment challenges, and solutions. The results of mechanical and lithographic slit manufacturing are discussed on optical spectrometers applications for earth observation, which are used on the DESIS-, the Sentinel 4 - and the FLEX-instrument.