Underwater Laguerre-Gaussian beam propagation and phase compensation method

Abstract

Laguerre-Gaussian (LG) beams experience phase twist after long-distance transmission, making the orbital angular momentum (OAM) indistinguishable. This phenomenon becomes more severe in water due to the higher refractive index. Based on the physical principles of LG beams, this paper derives the mathematical expression for LG beam transmission in water to address this issue. It organizes and analyses the physical significance of each term. The exponential term responsible for phase twist is separated and phase compensation is applied to the initial LG beam. Simulation results show that after transmission through water, traditional LG beams exhibit a clockwise twisted distribution of isophase lines. By applying the phase compensation method proposed in this paper, the phase of the initial LG beam is modulated and when the LG beam reaches the observation plane, the isophase lines become straight, verifying the effectiveness of the method. This compensation method holds significant value for LG beams in advanced physics research.