Christoph Damm

Development, fabrication, and testing of an anamorphic imaging snap-together freeform telescope

The fabrication chain for the development of an afocal all aluminum telescope using four anamorphic aspherical mirrors is described. The optical and mechanical design are intended to achieve an enhanced system integration with reduced alignment effort by arranging two optical surfaces monolithically on common mirror bodies. Freeform machining is carried out by a hybrid fabrication approach combining diamond turning and diamond milling in the same machine setup. A direct figure correction of diamond turned aluminum mirrors by magnetorheological finishing is presented, resulting in high-precision athermal mirror modules with excellent figure properties. The interferometric system test highlights the diffraction limited telescope performance and the feasibility of the chosen approaches for freeform machining and mechanical integration.

Ultra-precisely manufactured mirror assemblies with well-defined reference structures

Aspherical surfaces for imaging or spectroscopy are a centerpiece of high-performance optics. Due to the high alignment sensitivity of aspheric surfaces, reference elements and interfaces with a tight geometrical relation to the mirror are as important as the high quality of the optical surface itself. The developed manufacturing method, which accounts for the shape and also for the position of the mirror surfaces, allows controlling and precisely correcting not only the form, but also the alignment of reference marks, interfaces or even other mirrors in the sub-assembly using diamond turning. For Korsch or TMA telescopes it is also possible to diamond turn whole sub-assemblies containing two or more mirrors with a relative position error as low as the machine precision. Reference elements allow the correction of the shape and position of mirrors as well as the position of interfaces for system integration. The presented method opens up a novel manufacturing strategy to enhance the relative positioning accuracy of optic assemblies by one order of magnitude.

Novel TMA telescope based on ultra precise metal mirrors

Modern telescopes for space applications use complex optical elements like aspheres or freeforms. For the multispectral pushbroom scanner for spaceborne Earth remote sensing the Jena-Optonik GmbH has developed a Jena-Spaceborne- Scanner JSS product line. The optic of JSS-56 imager is realised by a Three-Mirror-Anastigmat (TMA) telescope designed in aluminium [1]. For brilliant pictures, mirrors with high shape accuracy and very smooth surfaces are required. The combination of precise diamond turning and post polishing techniques enables the classical infrared application for the visible and ultra-violet range. A wide variety of complex mirror shapes are feasible. A special new solution for lightweight design was applied. Ultra precise metal mirrors with aspherical surface are developed at the Fraunhofer IOF from design to system integration. This paper summarizes technologies and results for design, fabrication and surface finish of ultra lightweight aspherical metal mirrors for novel TMA telescopes.

Temporally-stable active precision mount for large optics.

We present a temporally-stable active mount to compensate for manufacturing-induced deformations of reflective optical components. In this paper, we introduce the design of the active mount, and its evaluation results for two sample mirrors: a quarter mirror of 115 × 105 × 9 mm3, and a full mirror of 228 × 210 × 9 mm3. The quarter mirror with 20 actuators shows a best wavefront error rms of 10 nm. Its installation position depending deformations are addressed by long-time measurements over 14 weeks indicating no significance of the orientation. Size-induced differences of the mount are studied by a full mirror with 80 manual actuators arranged in the same actuator pattern as the quarter mirror. This sample shows a wavefront error rms of (27±2) nm over a measurement period of 46 days. We conclude that the developed mount is suitable to compensate for manufacturing-induced deformations of large reflective optics, and likely to be included in the overall systems alignment procedure.

MERTIS: optics manufacturing and verification

The MERTIS reflective infrared optics can be beneficial implemented as diamond turned aluminium mirrors coated with a thin gold layer. The cutting processes allow the manufacturing of both, the optical surface and mechanical interfaces, in tight tolerances. This is one of the major advantages of metal optics and was consequently used for the MERTIS sensor head optics. This paper describes the entire process chain of the MERTIS spectrometer optics including the manufacturing methods for the mirrors and for the spherical grating, the coating with sputtered gold for infrared reflectivity as well as the alignment and the verification of the spectrometer optics.

Schwarzschild-objective-based EUV micro-exposure tool

Diffraction limited 20x Schwarzschild objectives have been fabricated for various applications at 13.5nm wavelength. For this purpose the major parts of the whole technology chain for the realization of diffraction limited reflective optical systems working in the EUV spectral region have been established. This chain includes: optical design of the system, mechanical construction of mounting structures on the basis of extensive stress and thermal analysis, development of adhesive free mountings, high-reflective Mo/Si multilayer coatings for use at 13.5nm wavelength, assembly of the whole objective system, development of adapted semiconductor detectors for 13.5nm. The realized Schwarzschild objectives with a numerical aperture of NA=0.2 have been integrated into different optical set-ups such as a table top scanning micro exposure tool and an EUV microscope. The EUV micro exposure tool is currently used for various EUVL-related applications such as investigations of resolution limiting factors and EUV resist sensitivity test stand. Properties and performance of both the Schwarzschild objective and the optical set-up are presented in the paper.

Wafer stage assembly for ion projection lithography

In the framework of the Ion Projection Lithography project a wafer stage with nanometer position stability was developed. Major components were fabricated from glass ceramics to meet the requirements for mechanical and thermal stability as well as for minimum magnetic susceptibility.

Design of an imaging spectrometer for earth observation using freeform mirrors

In 2017 the new hyperspectral DLR Earth Sensing Imaging Spectrometer (DESIS) will be integrated in the Multi-User-System for Earth Sensing (MUSES) platform [1] installed on the International Space Station (ISS).

Anamorphotic telescope for earth observation in the mid-infrared range

In the framework of the “Earth Explorer” program, the European Space Agency had foreseen the PREMIER mission intended to monitor the three-dimensional distribution of trace gasses in the atmosphere.

Thermal infrared spectrometer MERTIS for the BepiColumbo Mission to Mercury

The MERTIS instrument is a thermal infrared imaging spectrometer onboard of ESAs cornerstone mission BepiColombo to Mercury. MERTIS will provide detailed information about the mineralogical composition of Mercurys surface layer by measuring the spectral emittance in the spectral range from 7-14 μm with a high spatial and spectral resolution. Furthermore MERTIS will obtain radiometric measurements in the spectral range from 7-40 μm to study the thermo-physical properties of the surface material. Under the lead of the German Aerospace Center DLR (Dep. Optical Information Systems, Berlin) a development model (DM) is in development which integrates all MERTIS sub-units of later flight models. With the DM the general design and performance goals of the system shall be investigated and verified. Besides a general overview about the instrument principles the following topics are addressed: Optics setup with a Three Mirror Anastigmatic (TMA) telescope and Offner Spectrometer, Manufacturing techniques for the robust and high precision optics and Radiometer Concept and Design