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Proceedings Paper

Optimal beam steering using time-delayed wavefront measurements in airborne laser target engagements
Author(s): Matthew R. Whiteley; Michael C. Roggemann; Byron M. Welsh
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Paper Abstract

In Airborne Laser (ABL) target engagements, beam steering should account for the effects of turbulence-induced wavefront tilt. Due to the finite temporal response of adaptive-optical systems, steering commands must be based upon time-delayed wavefront measurements. The dynamics of the ABL target engagement scenario and turbulence-induced anisoplanatism cause the time-delayed wavefront measurements to be decorrelated from the required wavefront tilt correction. This decorrelation leads to suboptimal beam steering when time-delayed wavefront measurements are used directly in the control loop. To assess beam steering performance, we calculate the aperture-averaged mean square residual phase error after tilt correction, as a function of measurement time delay, and show that this quantity is minimized by the minimum mean square error (MMSE) estimate of tilt given a set of time-delayed wavefront measurements. Therefore, a temporal MMSE tilt estimator is constructed using time-delayed tilt plus higher-order aberration measurements. We define the tilt correction interval (tau) c as the time delay at which the residual phase error is 1% larger than its value at zero time delay. Our results show that (tau) c using the MMSE tilt estimator with modal measurements through Zernike 15 is over 3 times larger than (tau) c using time-delayed tilt measurements only. Accordingly, the beam steering bandwidth for ABL target engagements is reduced by more than 70% when higher order modal measurements are used in optimal tilt correction.

Paper Details

Date Published: 8 September 1998
PDF: 12 pages
Proc. SPIE 3381, Airborne Laser Advanced Technology, (8 September 1998); doi: 10.1117/12.323929
Show Author Affiliations
Matthew R. Whiteley, Air Force Institute of Technology (United States)
Michael C. Roggemann, Michigan Technological Univ. (United States)
Byron M. Welsh, Air Force Institute of Technology (United States)

Published in SPIE Proceedings Vol. 3381:
Airborne Laser Advanced Technology
Todd D. Steiner; Paul H. Merritt, Editor(s)

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