Adaptive Control for Aero-Optical Compensation
Depiction of adaptive controller functionality,
which the test bed can evaluate/compare to that
of conventional controllers. The spatial light
modulator can add disturbances to the beam
before correction by the deformable mirror, with
the beam sensed by the wavefront sensor and
scoring camera. (AFRL Image)
(www.wpafb.af.mil) AIr Force Research Laboratory Small Business Innovation Research addressed the Air Force requirement for robust adaptive optics beam control in airborne laser directed energy systems, a capability enabling such systems to maintain optical quality throughout a laser's traverse of its path from aircraft to target. Specifically, the SBIR effort--conducted by MZA Associates Corporation--developed an adaptive control method that can be incorporated into any wavefront control processor. Compared to conventional control methods, this breakthrough technique doubles the laser irradiance delivered to targets from the laser system. Consequently, by removing significant aero-optical distortions, this high-performance AO capability could immediately benefit aircraft laser systems and the warfighters who operate them.
The propagation path of an aircraft laser beam includes optical disturbances caused by the airflow around the aircraft, commonly referred to as "aero-optics," as well as naturally occurring atmospheric turbulence over the many kilometers of air through which the laser passes. Aero-optic control technology greatly improves the quality of the laser compensation, given the characteristics of the beam control system and the flight/atmospheric conditions. In turn, improved laser compensation increases the laser irradiance incident upon a target.
Adaptive control refers to the logic and accompanying computer software that connects optical disturbance measurements taken by the beam control system's wavefront sensor with the commands sent to the deformable mirror, which then corrects the laser for optical distortions. Since the AO system must be updated several thousand times per second in order to measure aero-optical disturbances, latencies in the AO system result in adaptive optical compensation degradation.