In-flight measurement of atmospheric-imposed tilt: experimental results and analysis

The work presented here experimentally measures the tilt imposed on a laser beam by the atmosphere from Shack-Hartmann wavefront sensor measurements collected in-flight. Tip/tilt is imposed on the laser beam by propagating through optical turbulent structures larger than or of the order of the size of the beam diameter. This tip/tilt causes a dynamic, net deflection of the beam in the far field, referred to as jitter, which poses a serious problem for tracking in directed energy applications. The practical measurement of turbulence-induced tip/tilt at altitude is challenging since mechanical contamination in the form of vibrations also manifests as tip/tilt. In this paper, a procedure referred to as the stitching method is used to quantify the turbulence-induced component of tilt without the influence of mechanical corruption. It is found that the measured tilt aligns with what analytic solutions predict and that the turbulent environment through which the beam propagates has Kolmogorov-like characteristics.