Ray-tracing for coordinate knowledge in the JWST Integrated Science Instrument Module

TL;DR

This paper details the use of a matrix/vector ray tracing system for optical alignment, testing, and coordinate knowledge in the JWST's Integrated Science Instrument Module, demonstrating its practical application in optical engineering.

Contribution

It introduces a comprehensive ray tracing system that supports optical alignment, testing, and coordinate determination for the JWST instrument module, with a focus on real-system measurement and analysis.

Findings

Successful implementation of the ray tracing system in experimental data

Demonstrated capability for in situ monitoring of optical parameters

Validated the mathematical basis of the matrix/vector ray tracing model

Abstract

Optical alignment and testing of the Integrated Science Instrument Module of the James Webb Space Telescope is underway. We describe the Optical Telescope Element Simulator used to feed the science instruments with point images of precisely known location and chief ray pointing, at appropriate wavelengths and flux levels, in vacuum and at operating temperature. The simulator's capabilities include a number of devices for in situ monitoring of source flux, wavefront error, pupil illumination, image position and chief ray angle. Taken together, these functions become a fascinating example of how the first order properties and constructs of an optical design (coordinate systems, image surface and pupil location) acquire measurable meaning in a real system. We illustrate these functions with experimental data, and describe the ray tracing system used to provide both pointing control during operation and analysis support subsequently. Prescription management takes the form of optimization and fitting. Our core tools employ a matrix/vector ray tracing model which proves broadly useful in optical engineering problems. We spell out its mathematical basis, and illustrate its use in ray tracing plane mirror systems relevant to optical metrology such as a pentaprism and corner cube.