Scintillation Reduction for Laser Beams Propagating Through Turbulent Atmosphere

TL;DR

This paper investigates how to reduce laser beam scintillation caused by atmospheric turbulence, proposing novel methods involving partially coherent beams and combining Gaussian and vortex beams to improve long-distance laser communication.

Contribution

It introduces a new approach using partially coherent beams with specific initial directions and a novel method combining Gaussian and vortex beams to significantly reduce scintillation index.

Findings

Using sets of PCBs with specific directions reduces beam wandering.

Combining Gaussian and vortex beams with different frequencies suppresses scintillation.

The methods enable higher data rates in turbulent atmospheric conditions.

Abstract

We numerically examine the spatial evolution of the structure of coherent and partially coherent laser beams, including the optical vortices, propagating in turbulent atmospheres. The influence of beam fragmentation and wandering relative to the axis of propagation (z-axis) on the value of the scintillation index (SI) of the signal at the detector is analyzed. These studies were performed for different dimensions of the detector, distances of propagation, and strengths of the atmospheric turbulence. Methods for significantly reducing the scintillation index are described. These methods utilize averaging of the signal at the detector over a set of partially coherent beams (PCBs). It is demonstrated that the most effective approach is using a set of PCBs with definite initial directions of propagation relative to the z-axis. This approach results in a significant compensation of the beam wandering which in many cases is the main contributor to the SI. A novel method is to generate the PCBs by combining two laser beams - Gaussian and vortex beams, with different frequencies (the difference between these two frequencies being significantly smaller than the frequencies themselves). In this case, the effective suppression of the SI does not require high-frequency modulators. This result is important for achieving gigabit data-rates in long-distance laser communication through turbulent atmospheres.