Characterizing the characterization of laser propagation through the atmosphere using a colinear Shack Hartmann wavefront sensor

Predicting laser beam propagation through a turbulent atmosphere is critical to applications such as directed energy (DE), free-space optical (FSO) communications, and astronomical imaging^1–3. A major challenge is that wavefront sensors and meteorological (MET) instruments are often deployed off-axis from the actual beam path, leading to potential errors in turbulence estimation and degraded model predictions^4–6. This study presents the design of a novel experimental framework to quantify the discrepancy between offaxis and on-axis turbulence measurements using a dual Shack-Hartmann Wavefront Sensor (SHWFS) setup. A ruggedized SHWFS with a meteorological sensor suite is deployed adjacent to the beam path, while a largeaperture telescope is aligned with the true beam propagation axis and integrated with a second SHWFS. Both sensors observe a downrange LED beacon, enabling simultaneous characterization of atmospheric distortions along distinct geometries. Each sensor’s turbulence estimates are used as inputs to scaling law models (MODTRAN, LEEDR, and custom tools) to predict far-field beam performance metrics such as peak irradiance and power-in-the-bucket (PIB).^{7, 8} These predictions are then compared to the actual beam delivered by the large-aperture telescope, providing a direct benchmark against which the predictive value of each sensing geometry can be assessed. By analyzing these discrepancies, this experiment will evaluate the operational limits of surrogate (off-axis) measurements and identify when direct alignment is necessary for accurate modeling of high-precision laser systems in turbulent environments.