Physical optics model for simulating the optical performance of the NIRSpec

The James Webb Space Telescope (JWST) Observatory, the follow-on mission to the Hubble Space Telescope, will yield astonishing breakthroughs in infrared space science. One of the four instruments on that mission, the NIRSpec instrument, is being developed by the European Space Agency with EADS Astrium Germany GmbH as the prime contractor. This multi-object spectrograph is capable of measuring the near infrared spectrum of at least 100 objects simultaneously at various spectral resolutions in the 0.6 μm to 5.0 μm wavelength range. A physical optical model, based on Fourier Optics, was developed in order to simulate some of the key optical performances of NIRSpec. Realistic WFE maps were established for both the JWST optical telescope as well as for the various NIRSpec optical stages. The model simulates the optical performance of NIRSpec at the key optical pupil and image planes. Using this core optical simulation module, the model was expanded to a full instrument performance simulator that can be used to simulate the response of NIRSpec to any given optical input. The program will be of great use during the planning and evaluation of performance testing and calibration measurements.