Next-Generation Beam Quality for Deployed Laser Systems
Stephen Ammons | 20-ERD-046
Light propagating through the atmosphere encounters turbulence generated by index-of-refraction fluctuations that distort image or beam quality. While deformable mirrors (DM) used in adaptive optics (AO) exist to combat this challenge, the wave-front sensing technology critical to AO system's function lags behind. We have developed a flexible, tunable sensor with the potential sensitivity of an interferometer and the maximum dynamic range exceeding the Shack-Hartmann sensor. Starting from the pyramid sensor pioneered in the astronomical community, we have modified the sensor to have tunable modulation leveraging LLNL's light field directing array. This effort utilized the low-latency adaptive mirror system (LLAMAS), a > 20 kHz closed-loop, real-time AO system. LLAMAS achieves bandwidths of 740 Hz on blown turbulence, an order-of-magnitude improvement over the Gemini planet imager and factor of two improvement over state-of-the-art competing systems. We implemented a computationally efficient LQG predictive control scheme in LLAMAS and experimentally demonstrated an improvement in performance using real windblown turbulence. We have also developed a computational fluid dynamical model of high-average-power laser cavities that predicts thermal cooling as a function of amplifier design parameters. We showed that the introduction of features in the wind-vane design can improve the cooling nature of the gas flow.
Stable imaging and laser propagation through optical aberration are important for a range of applications in astronomy, remote sensing, communications, and national security. This program supports the Laboratory's efforts through the laser and optical science and technology competency to field fully engineered laser-propagation systems and adaptive-optics systems for NIF&PS lasers. This program also leverages the Laboratory's considerable high-performance computing (HPC) modeling and simulation capabilities to understand supersonic turbulent flow in aerospace systems. This program has produced the highest bandwidth published AO system and has demonstrated techniques for compensating fast, flowing turbulence. As a result of this work, new U.S. government funding was obtained to field a laser guide star AO system utilizing a pyramid wave-front sensor on a one-meter telescope.
Publications, Presentations, and Patents
Nguyen, J. et al. 2021. "Trigonometric Parallaxes of Two T Dwarfs with Keck and Shane AO Astrometry." Publications of the Astronomical Society of the Pacific 133, 1026 (2021); doi: 10.10881538-3873/ac17e3. LLNL-JRNL-821003.
Ward-Duong, K. et al. 2021. "Gemini Planet Imager Spectroscopy of the Dusty Substellar Companion HD 206893 B." The Astronomical Journal 161, 5 (2021); doi: 10.3847/1538-3881/abc263. LLNL-JRNL-829711.