The Atmospheric Transmission Properties And Generation Technique Of Laser Beam At Middle Infrared

Free space optical communication due to strong collimation and good security and many other advantages,has become a research hotspot.Traditional near-infrared band of laser propagation in the atmospheric channel are highly susceptible to atmospheric attenuation and atmospheric turbulence,losing energy during the transmission process and diverging propagation direction which affect the quality of communication.While mid-infrared band,having advantages of atmospheric channel transmission,has been neglected because of its related devices.This paper focuses on the generation and atmospheric transmission characteristics of the mid-infrared band laser.Using the difference frequency generation technology and quasi phase matching principle,we obtain wide tuing and high stability mid-infrared laser through doped MgO lithium niobate crystal(MgO :PPLN).Two narrow linewidth continuous light source at 1083 nm and 1550 nm are used as the pump light and signal light.When the pump light power and signal light power are amplified to 2.8 W and 3.5 W,the maximum power of idler light power will be 3.2 mW within dithering.of 2.8% Mid-infrared laser light source can be achieved ranging over 3547.6 nm to 3629.1 nm by changing the wavelength of signal light.According to the absorption and scattering effected by atmosphere channel,we compare the mid-infrared band and near-infrared band.Using the HITRAN software providing the USA atmospheric model,we compare the absorption rate of two wavelengths at different propagation distance.Results show the mid-infrared wavelengths has lower absorption rate in highly water environment at long propagation distance.Then compare different scattering characteristics of two wavelength photons through single photon multiple scattering mode by the Monte Carlo method.Results show that the photons at mid-infrared wavelength receving the surface are more concentrated,the center of the relative light intensity is 1.6 times of.near infrared wavelengths.At the same time,under the condition of low visibility and long distance the transmission of mid-infrared wavelength is double than the near infrared.Finally we analyze the influences of atmospheric turbulence at mid-infrared band and near-infrared band.Compare the scintillation index effected by propagation distance and beam expansion effected by the initial waist radius under different turbulences.Results show the mid-infrared wavelengths have apparently advantages over flicker index and beam expanding under the condition of long propagation distance.The analysis results of composite attenuation effect and turbulence effect reveal that the mid-infrared band have obvious advantages over near-infrared band in a relatively harsh conditions for long distance transmission...