Angle-of-arrival variability of retroreflected lasers despite atmospheric reciprocity
S. Walsh, A. Frost, L. Howard, D.R. Gozzard, S. Karpathakis, B.P. Dix-Matthews, C. Gravestock, A. McCann, and S.W. Schediwy. Angle-of-arrival variability of retroreflected lasers despite atmospheric reciprocity. Optics Letters 47 (2022) 1920.
Abstract
Corner cube retroreflectors are commonly used as cooperative targets in free-space laser applications. The previous literature suggests that due to path reciprocity, a retroreflected beam is self-corrected across a turbulent atmosphere and should show no angle-of-arrival variability in the near field. This is at odds with recent experiments that rely on angle-of-arrival measurements in retroreflected beams for effective tip/tilt correction. In this Letter we investigate the mechanism behind observed angle-of-arrival variability using numerical field propagation to model various transceiver and retroreflector geometries. We determine that asymmetric truncation of a curved wavefront at the retroreflector, transceiver, or both, results in a difference in tip/tilt between the transmitted and reflected wavefronts. This difference propagates as angle-of-arrival variation at the transceiver despite reciprocity, providing the error signal necessary for adaptive optics tip/tilt correction without a remote beacon.