Improved beam jitter control methods for high energy laser systems

Abstract

The objective of this research was to develop beam jitter control methods for a High Energy Laser (HEL) testbed. The first step was to characterize the new HEL testbed at NPS. This included determination of natural frequencies and component models which were used to create a Matlab/Simulink model of the testbed. Adaptive filters using Filtered-X Least Mean Squares (FX-LMS) and Filtered-X Recursive Least Square (FX-RLS) were then implemented. Disturbance sources included narrowband mechanical vibration of the optical bench as well as broadband atmospheric turbulence (simulation only). A feedback controller with adaptive filter (or feedbacktype adaptive filter) was applied to a multi-rate video tracking loop, which required precise plant identification to prevent instabilities. A strapdown type Inertial Reference Unit (IRU) system was investigated using a reference laser, Position Sensing Device (PSD), Fiber Optic Gyro (FOG), and Fast Steering Mirror (FSM). The controller of the strapdown type IRU system consisted of a feedforward gyro signal in parallel with a feedback PSD signal. A Video tracking control system was simulated and tested on the HEL testbed. The IRU strapdown controller was simulated and preliminary tests conducted. Simulation and experimental results demonstrated superior performance over classical control methods.