The near-infrared spectrograph (NIRSpec) is a complex instrument that will be launched on board the James
Webb Space Telescope (JWST). It is composed of three three-mirror anastigmats (TMAs) made of silicon carbide
(SiC). Sagem REOSC has been in charge of the mirror polishing, coating, alignment and testing, as well as
cryogenic testing. The performance level and the alignment constraints, along with the polishing and alignment
processes, have led to the set up of a model to accurately predict the final performances of each TMA, and
minimize the risk of vignetting. The model has then been fitted to the measured parameters obtained after
alignment (wavefront error, magnification or focal length...) to get an accurate modelization of the actual
performances, and allow their evaluation on the full field of view. The model has been finally delivered with
each TMA, as a basis for the instrument performance simulator. We will show a good correlation between the
predicted performance (before alignment, obtained from individual mirror data) and the final performance (after
alignment), as well as a very good fit between the as-built models and the actual TMAs.© (2012) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Citation
François Riguet
"Predict and simulate final optical performances of TMAs: application to the NIRSpec instrument", Proc. SPIE 8550, Optical Systems Design 2012, 85501A (December 18, 2012); doi:10.1117/12.981203; http://dx.doi.org/10.1117/12.981203
