Extended capture range for focus-diverse phase retrieval in segmented aperture systems using geometrical optics

Abstract

Extending previous work by Thurman on wavefront sensing for segmented-aperture systems, we developed an algorithm for estimating segment tips and tilts from multiple point spread functions in different defocused planes. We also developed methods for overcoming two common modes for stagnation in nonlinear optimization-based phase retrieval algorithms for segmented systems. We showed that when used together, these methods largely solve the capture range problem in focus-diverse phase retrieval for segmented systems with large tips and tilts. Monte Carlo simulations produced a rate of success better than 98% for the combined approach.

James Webb Space Telescope Optical Simulation Testbed I: overview and first results

“…The wavefront sensing and control technologies chosen for JWST have been proven by a long-term technology development plan of simulations and laboratory demonstrations, 6 in particular using the Testbed Telescope (TBT) at Ball Aerospace, 7, 8 a 1:6 scale mockup of JWST with flight-like segmentation and actuation, and the Integrated Telescope Model (ITM) software. 9 However, new and improved algorithms for wavefront sensing and control continue to be developed, [10][11][12][13] and a flexible general-purpose lab testbed will contribute to evaluating such algorithms for possible application to JWST or to future missions such as WFIRST/AFTA. Furthermore, there is a continued need to practice scenarios and develop staff expertise for JWST commissioning and operations, including in the longer run a need for occasionally training new staff in phase retrieval techniques throughout the five-to-ten year mission of JWST.…”

Extending capture range for piston retrieval in segmented systems

“…It was common in the failed retrievals that a single segment would have a large amount of tilt, which would cause the energy to overlap with another segment's energy in some frames. This has been observed before, and can be countered by using a geometrical optics approach that ensures that light from neighboring segments does not overlap in the modeled PSFs if it does not overlap in the data [8,21]. The results in Table 1 show overall that the algorithm is robust to additional per-segment RMS WFE of up to 0.2λ 0 , and additional global RMS WFE of up to 0.25λ 0 ; that is, the probability of success for any one retrieval is high enough that with a few different random starting guesses, we can expect a successful retrieval with high probability.…”

“…The capture range for a given system can be extended through taking a diversity of additional measurements and adapting the model to be consistent with these measurements [5][6][7]. Random starting points or auxiliary system information can also be used to perform a global search without changing the capture range of the optimization algorithm itself [8,9].…”

Quantifying telescope phase discontinuities external to adaptive optics systems by use of phase diversity and focal plane sharpening

“…In the context of Phase Diversity and Phase Retrieval, the exploration of induced diversity has been investigated by numerous examples in the literature. For example, Jurling et al (2014) 20 consider scenarios with +/-8 waves of focus diversity. Therefore, we acknowledge that it is possible alternative diversities may be more desirable, but for the purposes of this work we do not further pursue this topic.…”