Journal of Atmospheric and Environmental Optics ›› 2020, Vol. 15 ›› Issue (1): 40-47.

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Influence of Beam Parameters on Propagation of Blue Green Laser Underwater

Influence of Beam Parameters on Propagation of Blue Green Laser Underwater   

  1. Key Laboratory of Space Laser Communication and Detection Technology, Shanghai Institute of Optics 
    and Fine Mechanics, Chinese Academy of Sciences,\quad Shanghai 201800, China
  • Online:2020-01-28 Published:2020-01-19

Abstract: The blue-green spectrum in the range of 450$\sim$550 nm is the only low loss optical window of seawater. 
Due to the absorption and scattering of water, the underwater propagation of the laser beam will 
have time-space expansion and waveform distortion. Based on Monte Carlo simulation, the propagation 
characteristics of blue-green laser in seawater have been analyzed, especially the influence of laser 
emission parameters on the distribution of receiving light field. By adjusting the beam parameters 
of the transmitter and focusing the laser beam in advance, the influence of beam diffusion caused 
by underwater transmission can be eliminated to some extent. The analysis and simulation results 
show that when the pre-focusing angle is equal to the small angle scattering eigenvalue of water, 
a flat transmission area with slow spread of laser beam can be formed in Jerlov type IB water before 
the designed focus distance. When the pre-focusing angle is greater than twice 
the scattering angle 
of water, the convergence effect can be formed near the designed focus distance, and the focus effect 
is proportional to the pre-focusing angle. When the water quality becomes worse, the corresponding 
effective focus distance becomes shorter. The research results provide a new way to improve the 
transmission characteristics of blue-green laser signal in seawater. 

Key words: blue-green laser, Monte Carlo simulation, beam pre-focusing, scattering, ocean propagation characteristics

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