Studies of the Pressure Field and Related Beam Jitter for Hemisphere-on-Cylinder Turrets

Beam jitter is defined as the unsteady variation of a laser beam’s propagation direction. For airborne directed energy systems that feature turrets, the high speed flow around the aircraft introduces jitter into the system. The jitter has two main forms: mechanical jitter from vibration induced by the unsteady pressure field over the turret and aero-optical jitter from large scale structures that impose aberrations with length scales larger than the beam aperture. Beam jitter is highly dependent on the specific geometry and construction of a directed energy turret as surface geometry changes will modify the flow field over the turret and interior construction changes will alter the vibrational modes. This dissertation investigates the exact character of jitter over a specific turret geometry. This is done through surface pressure, jitter and vibration measurements to not only separate the total jitter into aero-optical and mechanical components, but also determine which flow features over a turret drive the two different forms of jitter. The techniques presented in this dissertation can be applied to characterize the jitter of any given directed energy system. A few guidelines to mitigate potential jitter in future turret designs are also given.