Optical wavefront characterization using phase retrieval for the NIRSpec demonstration model for the James Webb Space Telescope

Phase retrieval results are presented for the James Webb Space Telescope (JWST) Near InfraRed Spectrograph (NIRSpec) demonstration model (DM). NIRSpec is one of five science instruments (SIs) comprising the Integrated Science Instrument Module (ISIM); the NIRSpec is being built for the European Space Agency by a consortium led by EADS Astrium GmbH. During this initial DM test campaign, focal-sweep images were collected over the science field of view (FOV) for determining best focus at both ambient and cryogenic (cryo) temperature environments, and these images were then used as input to the Hybrid Diversity Algorithm (HDA) for phase retrieval, using Variable Sampling Mapping (VSM). Wavefront estimates from phase retrieval, an error budget, and diagnostics used to assess phase retrieval stability and convergence are discussed. The ambient phase retrieval results were compared against wavefront measurements taken with a Shack-Hartmann wavefront sensor.