Tracking and imaging under atmospheric conditions

Abstract

Tracking and imaging systems are important add-ons for laser systems being used under atmospheric turbulent conditions. They can be used independently in different applications, but can also be combined advantageously e.g. in high-power laser effectors. In this paper, we present high-end tracking and imaging systems currently being developed as technology demonstrators at the German Aerospace Center (DLR) in Stuttgart. The systems are regularly tested under real atmospheric conditions at the eye-safe high-power laser test range in Lampoldshausen near Stuttgart. The correction of turbulence effects with adaptive-optical compensated imaging is essential for target reconnaissance and tracking of aim-points on moving targets. A mobile system with a 6 inch Schmidt-Cassegrain telescope has successfully demonstrated its ability to compensate for local and distributed turbulence effects in laboratory and atmospheric environments. It has a feedback-loop bandwidth of 900 Hz and is capable to compensate for residual wavefront deformations down to 15 nm RMS. The system can correct phase distortions in a conjugated plane with time constants of 30 ms. Large bandwidth fine tracking units are successfully used to achieve the tip/tilt correction of atmospheric turbulence effects. We designed and engineered a tip/tilt system adapted to a 10” telescope which is able to counterbalance turbulence induced laser beam deflection down to the sub µrad range at distorting frequencies of several hundreds of Hz. Position detection is performed with quadrant detectors and the tip/tilt correction with Piezo actuator based mirrors. The performance of both systems was characterized and will be discussed in the paper including the technology potential and restrictions.