Anisotropic beam spread of a vortex beam in air-to-seawater wireless slant channels with wind and bubble

The anisotropic beam spread of a Laguerre-Gaussian beam in an air-to-seawater wireless slant path under wind and bubble fluctuations is investigated experimentally and theoretically for the first time, to our knowledge. The results indicate that large bubble fluctuations, high wind speed, low orbital angular momentum (OAM) quantum number, and low laser power reduce the beam spread along both the X axis and the Y axis. After accounting for the effects of laser power and OAM quantum number, it is shown that higher laser power can suppress beam spread induced by seawater in the slant path. Additionally, beam spread initially increases and then decreases with increasing OAM quantum number. In the absence of bubble fluctuations, seawater salinity difference and temperature difference have minimal impact on beam spread. A small zenith angle results in a small beam spread. Higher temperature difference leads to smaller beam spread along the X axis for all wind speeds and along the Y axis for wind speeds above 0.3 m/s. However, the beam spread in the Y axis for wind speed below 0.1 m/s first decreases, and then increases, with increasing temperature difference. Under bubble fluctuations, strong wind mitigates beam spread caused by the combination of high temperature difference and bubbles, but amplifies the spread resulting from low temperature difference and bubbles. Low wind speed exacerbates beam spread under the combined influence of bubbles and temperature difference. The effect of wind speed on beam spread is more pronounced in the presence of bubbles than in their absence. Bubble fluctuations also intensify the impact of seawater salinity differences on beam spread at small zenith angles. Furthermore, the proposed theoretical model effectively simulates the beam spread of a vortex beam under bubble and wind speed interference. The experimental and theoretical findings provide a valuable foundation for advancing air-to-seawater wireless optical communication and imaging.