The high precision double slit device of the slit assembly for the FLEX instrument

The high precision Slit Assembly is a key component of the FLEX instrument. Two different input beams for the Low- and the High-resolution spectrometer, respectively, will be generated by the Slit assembly. The paper presents design and implementation of its optical key components, which are a highly precise double slit and two mirrors achieving spatial channel separation and spectral filtering. High alignment and stability requirements, as well as stringent envelope restrictions are driving the mechanical design of the Slit Assembly. We demonstrate solutions in design and manufacturing techniques as well as achieved performance under thermal and mechanical loads. The main focus of the paper is on the development and realization of the double slit device. This device is designed to mount a silicon double slit chip into a mechanical holder providing mechanical and gauge interfaces to the slit assembly. The slit position is aligned to mechanical interfaces to meet the tight positioning requirements. A dedicated lithographic structuring process chain was developed for the manufacturing of the double slit to fulfill a number of challenging requirements; i.e. the absolute slit width accuracy of less than 2 μm peak to valley, and slit planarity of less than 10 μm peak to valley. It is based on the adaptation of lithographic structuring techniques for etching of Silicon wafers. The overall manufacturing process is the result of an extended technology development phase. The manufactured slits are coated with a black coating layer to reach the specified optical reflectivity and the optical density. The results of environmental tests of the Double slit device Breadboard, i.e. the thermal vacuum test, the shock test, and the vibration test, are discussed.