Analysis of Optical Telescope Element (OTE) used in James Webb Space Telescope (JWST)

Abstract

This paper presents an analysis of the James Webb Space Telescope (JWST) Optical Telescope Element (OTE) based on its published optical prescription and system architecture. Using modeling, key optical performance parameters were evaluated, including spot diagrams, footprint diagrams, wavefront error (WFE), point spread function (PSF), Strehl ratio, encircled energy (EE), and modulation transfer function (MTF). The segmented 6.6 m primary mirror was modeled using a User-Defined Aperture (UDA) approach to accurately reproduce the hexagonal pupil geometry and diffraction effects. Results confirm diffraction-limited performance across the evaluated field, with RMS wavefront error well below the Maréchal criterion, high Strehl ratios (≥0.87 off-axis and ≥0.97 on-axis at 1 µm), and encircled energy closely matching the diffraction limit. MTF curves demonstrate strong contrast transfer up to the cutoff spatial frequency with minimal field-dependent degradation.

Additional analyses were performed to assess the impact of individual segment piston and tilt misalignments. Controlled perturbations show that segment-level phase discontinuities significantly degrade WFE, emphasizing the importance of precise segment phasing and wavefront sensing and control (WFS&C).