Scaling Laws of Beam Spreading in Laser Ocean Turbulence
Objective As underwater military activities and scientific research are increasingly frequent,the demand for high-speed,high-quality,and high-bandwidth underwater communication has become urgent.However,laser communication effectiveness in seawater is hampered by the scattering,absorption,and turbulence effects,which causes degraded beam quality and increased communication error rates.Consequently,it is of application significance to study the beam quality degradation characteristics of blue-green lasers in seawater.However,laser propagation calculation in seawater turbulence is quite complex and time-consuming.Therefore,it is of significance to establish a beam expansion calibration formula,especially for blue-green laser propagation in seawater turbulence.This scaling law will enable the rapid prediction and evaluation of beam expansion influence and patterns.Methods First,we build a rigorous physical model to comprehend the propagation of blue-green lasers in seawater turbulence.By adopting the power spectrum inversion method,phase screens of seawater turbulence are generated to enable the numerical calculation of beam expansion variation,with both seawater parameters and laser parameters considered.Second,the β factor is employed to evaluate the energy concentration of laser beams on the target plane and thus revealing the beam expansion of lasers by seawater turbulence.Finally,a beam expansion calibration formula for blue-green lasers propagating in seawater turbulence is proposed via the processing method of the mean square sum.Results and Discussions The estimation results of the scaling law obtained by fitting are compared with those of numerical calculation.The results show that the scaling law matches well with the numerical calculation under certain laser and seawater turbulence parameters.This is under the scenario that the laser parameters fall within the ranges of 0.001-0.100 m for the beam waist radius,1.0-4.0 for the initial beam quality factor,470-550 nm for the wavelength,and-5.0--0.5 for the value range of temperature-induced seawater turbulence to salinity-induced seawater turbulence.Additionally,the seawater turbulence parameters are kinetic energy dissipation rate of 10-10-10-1m2/s3,and 10-10-10-4K2/s for the dissipation rate of temperature difference.After imposing this limitation,for the total beam expansion,the maximum error between the beam expansion estimated by the scaling law and the numerical calculation results is 10.90％,with a maximum average error of 4.70％.Consequently,the scaling law can accurately predict the beam expansion laws of Gaussian beams propagating in seawater turbulence.Conclusions To rapidly and accurately predict the beam expansion law of Gaussian beams propagating in seawater turbulence,we first analyze the variation of beam expansion with laser and seawater parameters.Subsequently,the scaling law for beam expansion of blue-green lasers in seawater turbulence is proposed.On this basis,the coefficients in the scaling law are determined by employing the least squares method.The scaling law is then utilized to estimate the errors between the beam expansion estimated by the scaling law and the numerical calculation results under different parameters.The results show that within the specified parameter range,the error between the estimated beam expansion law by the scaling law and the numerical calculation results is within 5％.
ocean turbulencebeam spreadingoptical propagationscaling law
NETL
NSTL
万方数据
