Matthew R. Bolcar

Sub-aperture piston phase diversity for segmented and multi-aperture systems

Phase diversity is a method of image-based wavefront sensing that simultaneously estimates the unknown phase aberrations of an imaging system along with an image of the object. To perform this estimation a series of images differing by a known aberration, typically defocus, are used. In this paper we present a new method of introducing the diversity unique to segmented and multi-aperture systems in which individual segments or sub-apertures are pistoned with respect to one another. We compare this new diversity with the conventional focus diversity.

Method of Phase Diversity in Multi-aperture Systems Utilizing Individual Sub-aperture Control

Multi-aperture systems allow a natural method of implementing phase diversity for the joint estimation of both pupil aberrations and an image of the object. Instead of creating diversity images by means of focus adjustments, one can actuate the individual sub-apertures of the system (e.g., with a piston phase) to introduce known phase diversity. Implementation of a nonlinear optimization routine is discussed. Through digital simulation, this paper investigates the performance of a sub-aperture piston diversity algorithm by tracking Strehl ratio and the probability and speed of convergence of the nonlinear optimization routine.

Phase Retrieval in Sparse Aperture Systems with Phase Diversity : A Trade Space Study

Sparse-aperture (SA) telescopes are a technology of interest in the field of remote sensing. Significant optical resolution can be achieved by an array of sub-apertures, mitigating size and weight limitations of full aperture space-deployed sensors. Much of the analysis to date has been done with the assumption that an extended scene is spectrally flat and each pixel has the same spectrum (gray-world assumption). Previous work has found the gray-world assumption is not valid when imaging a spectrally diverse scene and/or when the optical configuration is heavily aberrated. Broadband phase diversity (BPD) is an image-based method to detect the aberrations of a system. It also assumes a gray-world. Digital simulations that quantify the limitations of BPD with respect to spectral diversity of the extended scene, the RMS of the optical path difference (OPD), noise of the system, and band width of the sensor are presented.

Focus determination for the James Webb Space Telescope science instruments: a survey of methods

The James Webb Space Telescope (JWST) is a segmented deployable telescope that will require on-orbit alignment using the Near Infrared Camera as a wavefront sensor. The telescope will be aligned by adjusting seven degrees of freedom on each of 18 primary mirror segments and five degrees of freedom on the secondary mirror to optimize the performance of the telescope and camera at a wavelength of 2 microns. With the completion of these adjustments, the telescope focus is set and the optical performance of each of the other science instruments should then be optimal without making further telescope focus adjustments for each individual instrument. This alignment approach requires confocality of the instruments after integration and alignment to the composite metering structure, which will be verified during instrument level testing at Goddard Space Flight Center with a telescope optical simulator. In this paper, we present the results from a study of several analytical approaches to determine the focus for each instrument. The goal of the study is to compare the accuracies obtained for each method, and to select the most feasible for use during optical testing.

Phase and Pupil Amplitude Recovery for JWST Space-Optics Control

Phase and pupil amplitude recovery are presented for the JWST NIRCam using OMA test data. Two algorithm approaches are considered to establish error bars and to provide an optical characterization of the NIRCam.

A Comparison of Regularized Metrics for Phase Diversity

We compare the performance of four metrics for use in a phase diversity algorithm. Three of the metrics utilize a regularization based on the signal-to-noise ratio.

Modelling exoplanet detection with the LUVOIR coronagraph (Conference Presentation)

The Coronagraph is a key instrument on the Large UV-Optical-Infrared (LUVOIR) Surveyor mission concept. The Apodized Pupil Lyot Coronagraph (APLC) is one of the baselined mask technologies to enable 1E10 contrast observations in the habitable zones of nearby stars. The LUVOIR concept uses a large, segmented primary mirror (9--15 meters in diameter) to meet its scientific objectives. For such an observatory architecture, the coronagraph performance depends on active wavefront sensing and control and metrology subsystems to compensate for errors in segment alignment (piston and tip/tilt), secondary mirror alignment, and global low-order wavefront errors. Here we present the latest results of the simulation of these effects for different working angle regions and discuss the achieved contrast for exoplanet detection and characterization under these circumstances, including simulated observations using high-fidelity spatial and spectral models of planetary systems generated with Haystacks, setting boundaries for the tolerance of such errors.

The wide-field spatio-spectral interferometer: system overview, data synthesis and analysis

The Wide-field Imaging Interferometry Testbed (WIIT) is a double Fourier (DF) interferometer operating at optical wavelengths, and provides data that are highly representative of those from a space-based far-infrared interferometer like SPIRIT. We have used the testbed to observe both geometrically simple and astronomically representative test scenes. Here we present an overview of the astronomical importance of high angular resolution at the far infrared, followed by the description of the optical set-up of WIIT, including the source simulator CHIP (Calibrated Hyperspectral Image Projector). We describe our synthesis algorithms used in the reconstruction of the input test scenes via a simulation of the most recent measurements. The updated algorithms, which include instruments artifacts that allow the synthesis of DF experimental data, are presented and the most recent results analyzed.

Estimation of Object Spectral Content Using Phase Diversity

We present a method of estimating object spectral content using phase diversity with a grey-world assumption. Operation of a multi-aperture system is simulated, using sub-aperture piston phase diversity.

Comparison of Estimation Methods for Field-Dependent Phase Aberrations

Two techniques of multi-field phase retrieval are compared using digital simulations and Fisher Information theoretical methods. Results show solving for phase coefficients with explicit field-dependence yields a lower estimation error in the phase retrieval process.