Wavefront error performance characterization for the James Webb Space Telescope (JWST) Integrated Science Instrument Module (ISIM) science instruments
The science instruments (SIs) comprising the James Webb Space Telescope (JWST) Integrated Science Instrument Module (ISIM) were tested in three cryogenic vacuum test campaigns in the NASA Goddard Space Flight Center (GSFC)'s Space Environment Simulator (SES) test chamber. In this paper, we describe the results of optical wavefront error performance characterization of the SIs. The wavefront error is determined using image based wavefront sensing, and the primary data used by this process are focus sweeps, a series of images recorded by the instrument under test in its as used configuration, in which the focal plane is systematically changed from one image to the next. High precision determination of the wavefront error also requires several sources of secondary data, including 1) spectrum, apodization, and wavefront error characterization of the optical ground support equipment (OGSE) illumination module, called the OTE Simulator (OSIM) 2) f/ and pupil distortion measurements made using a pseudo nonredundant mask (PNRM) and 3) pupil geometry predictions for each SI field point tested, which are complicated because of a tricontagon shaped outer perimeter and small holes that appear in the exit pupil due to the way that different light sources are injected into the optical path by the OGSE. One set of wavefront error tests, for the coronagraphic channel of the Near Infrared Camera (NIRCam) Longwave instruments, was performed using data from transverse translation diversity (TTD) sweeps instead of focus sweeps, in which a subaperture is translated and/or rotated across the exit pupil of the system from one image to the next. Several optical performance requirements that were verified during this ISIM Element level testing are levied on the uncertainties of various wavefront error related quantities rather than on the wavefront errors themselves. This paper also gives an overview of the methodology, based on Monte Carlo simulations of the wavefront sensing analysis of focus sweep data, used to establish the uncertainties of the wavefront error maps.
Astronomical Telescopes Instrumentation