Laser beam propagation through a turbid heated medium: analysis of the positional impacts of the heat source

Abstract

The propagation characteristics of laser beams through the atmosphere are severely hampered by temperature fluctuations, which result in fluctuations of the refractive index in the air along its pathway. In this work, we analysed the effect of fluctuations formed from a thermal turbulence source on a propagating laser beam for two different positions of the thermal source. An experimental technique to quantify the positional impact of the thermal source on a 532 nm Gaussian laser beam deviations (wander) and profile (spreading) fluctuations under laboratory thermal conditions such as temperature and pressure were setup. The laser beam propagated through a point diffraction interferometer (PDI) before it was incident on a detector. Optical wavefront data of the major atmospheric characteristics such as the turbulence strength, Rytov variance (scintillation) and the coherence diameter (Fried’s parameter) were successfully extracted from the produced interferograms. The index structure constant showed strong turbulence ( $$C_{n}^{2}$$ ≥ 10−13 m−2/3), and it was stronger when the turbulence source is below the beam. The Rytov variances were in the weak scintillation range $$(\sigma_{R}^{2} \ll 1)$$ probably due to the short propagation distances. These results reveal that the location of the turbulence generator in the vicinity of a laser beam’s propagation path may strongly impact the physical characteristics including the beam wander, beam profile and intensity distribution.