We provide an overview of the design and capabilities of the near-infrared spectrograph (NIRSpec) onboard the James Webb Space Telescope. NIRSpec is designed to be capable of carrying out low-resolution (R = 30− 330) prism spectroscopy over the wavelength range 0.6 − 5.3µm and higher resolution (R = 500− 1340 or R = 1320− 3600) grating spectroscopy over 0.7 − 5.2µm, both in singleobject mode employing any one of five fixed slits, or a 3.1×3.2 arcsec 2 integral field unit, or in multiobject mode employing a novel programmable micro-shutter device covering a 3.6×3.4 arcmin 2 field of view. The all-reflective optical chain of NIRSpec and the performance of its different components are described, and some of the trade-offs made in designing the instrument are touched upon. The faint-end spectrophotometric sensitivity expected of NIRSpec, as well as its dependency on the energetic particle environment that its two detector arrays are likely to be subjected to in orbit are also discussed.

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

We report on an ultra-precise manufacturing method of a hyperspectral, mirror based IR-Telescope for applications in the Mid-wavelength infrared (MWIR). The proposed method simplifies the otherwise time consuming system alignment by the use of a snap-together assembly technique, that can be used for rotationally symmetric designs such as Korsch or Three Mirror Anastigmatic (TMA) telescope designs. The proposed technology is based on diamond machining of at least two mirror surfaces on one common substrate in one and the same machine setup. A novel hybrid manufacturing approach, which is a combination of diamond turning and diamond milling is used to manufacture fiducials and mounting planes that reduce the adjustment expenditure significantly. Reference elements and interfaces on the substrates are the basis for a precise metrology of the shape and the position of the optical surfaces as well as for the final assembly of the optical bench. The system integration into a hexapod framework is also based on precisely diamond machined stop surfaces to define the air distance and tilt between the mirrors. The presented method is a novel manufacturing and mounting technology for IR-telescope assemblies with diffraction limited optical performance in the MWIR

The development of smart alignment and integration strategies for imaging mirror systems to be used within astronomical instrumentation are especially important with regard to the increasing impact of non-rotationally symmetric optics. In the present work, well-known assembly approaches preferentially applied in the course of infrared instrumentation are transferred to visible applications and are verified during the integration of an anamorphic imaging telescope breadboard. The four mirror imaging system is based on a modular concept using mechanically fixed arrangements of each two freeform surfaces, generated by servo assisted diamond machining and corrected using Magnetorheological Finishing as a figuring and smoothing step. Surface testing include optical CGH interferometry as well as tactile profilometry and is conducted with respect to diamond milled fiducials at the mirror bodies. A strict compliance of surface referencing during all significant fabrication step s allow for an easy integration and direct measurement of the system's wave aberration after initial assembly. The achievable imaging performance, as well as influences of the tight tolerance budget and mid-spatial frequency errors, are discussed and experimentally evaluated

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