Experiments on Laser Beam Jitter Control with Applications to a Shipboard Free Electron Laser

A Free Electron Laser (FEL) shows potential as an effective defensive weapon for a naval ship against today’s modern weapons such as supersonic anti-ship missiles. A laser can destroy these fast and highly maneuverable missiles at the speed of light. Several obstacles must be overcome to employ this weapon on a naval ship. This thesis discusses several methods for passive and active jitter control of a guided optical beam which might be employed in a FEL weapon system. Vibration experiments were performed on the Laser Jitter Control Testbed at the Naval Postgraduate School to test several types of feedback and adaptive feedforward controllers. A Filtered-X Recursive Least Squares (FXRLS) adaptive feedforward controller was found to be most effective to correct a combination of both broadband and narrowband disturbances. The FXRLS controller results in a 33 dB decrease in jitter caused by a 50 Hz narrowband vibration and an 89% improvement in low frequency broadband jitter experienced by the optical beam. A proposed Free Electron Laser design employing both passive and active vibration control techniques is recommended that employs a co-linear optical reference beam for jitter control.