The Palomar Adaptive Optics System actively corrects for changing aberrations in light due to atmospheric turbulence. However, the underlying internal static error is unknown and uncorrected by this process. The dedicated wavefront sensor device necessarily lies along a different path than the science camera, and, therefore, doesn’t measure the true errors along the path leading to the final detected imagery. This is a standard problem in adaptive optics (AO) called “non-common path error.”
The previous method of calibrating this error consisted of manually applying different polynomial shapes (via actuator voltages) at different magnitudes onto the deformable mirror and noting if the final image quality had improved or deteriorated, before moving onto the next polynomial mode. This is a limited, time-consuming, and subjective process, and structural and environmental changes over time necessitate a new calibration over a period of months.
The Autonomous Phase Retrieval Calibration (APRC) software suite performs automated sensing and correction iterations to calibrate the Palomar AO system to levels that were previously unreachable. APRC controls several movable components inside the AO system to collect the required data, automatically processes data using an adaptive phase retrieval algorithm, and automatically calculates new sets of actuator voltage commands for the deformable mirror. APRC manages and preserves all essential data during this process.
The APRC software calculates the true wavefront error of the full optical system, then uses the existing AO system deformable mirror (DM) to correct the detected error. This provides a significant leap in performance by precisely correcting what were once “un-calibratable” errors. Furthermore, the corrective pattern found by this process serves as the underlying nominal shape of the DM, upon which the adaptive corrections for atmospheric turbulence are based.
This work was done by Siddarayappa A. Bikkannavar, Catherine M. O’Hara, and Mitchell Troy of Caltech for NASA’s Jet Propulsion Laboratory.
This software is available for commercial licensing. Please contact Daniel Broderick of the California Institute of Technology at
This Brief includes a Technical Support Package (TSP).
Autonomous Phase Retrieval Calibration
(reference NPO-47270) is currently available for download from the TSP library.
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Overview
The document is a Technical Support Package from NASA's Jet Propulsion Laboratory (JPL) detailing the Autonomous Phase Retrieval Control (APRC) system developed for the Palomar Adaptive Optics System. The APRC is an automated algorithm designed to improve the performance of optical systems by accurately measuring and correcting wavefront errors.
The APRC addresses the challenge of internal static aberrations that can affect the quality of astronomical images. By utilizing advanced algorithms, the system can retrieve precise wavefront information, which is crucial for enhancing the clarity and detail of images captured by telescopes. The document emphasizes the significance of achieving a residual controllable wavefront error of just 17 nanometers, showcasing the high level of precision that the APRC can achieve.
The Technical Support Package outlines the broader implications of this technology, suggesting that the advancements made in phase retrieval can have applications beyond astronomy, potentially benefiting various fields that rely on optical systems. The document also serves as a resource for those interested in the commercial and scientific applications of aerospace-related developments.
In addition to the technical details, the document includes contact information for further inquiries, emphasizing JPL's commitment to sharing knowledge and fostering partnerships through the NASA Innovative Partnerships Program. It also includes a disclaimer regarding the use of the information provided, clarifying that the U.S. Government does not assume liability for its application.
Overall, the document highlights the innovative work being done at JPL in the realm of adaptive optics and phase retrieval, illustrating how these advancements can lead to improved optical performance and contribute to the broader goals of space exploration and scientific discovery.
