Aero-Optical Effects Of Laguerre-Gaussian Vortex Beams

Turret is often used as an airborne platform of emitting and receiving targeting beams,directed-energy weapon guidance beams and free space optical communication(FSOC)beams.However,because of turret's non-optimal aerodynamic shape,when aircraft flying at a high speed,complex turbulent field will form around turret.Beams will jitter or deviate when they propagate through the turbulent boundary layer and therefore the beams will decline in quality.And although vortex beams as a hotpot of FSOC have been detailed studied when they propagate through atmosphere,their characteristics of propagation through turbulent field received little attention,while the fact is that their applications in military aeronautical communication and civil communication satellites are predictable future.Based on the background mentioned above,the research of the aero-optical effects of a typical vortex beam--Laguerre-Gaussian(LG)beams through two sets of turbulent fields which were formed respectively by a turret and a micro-turret(referred to as turret turbulent field and small-scale turbulent field respectively)has been done.Took LG beams with topological charges equaling p?05 1=1,2,3(referred to as LI,L2,L3)as research objects.Gaussian beam with the same beam waist as LG beams was used as comparison.Each set of turbulent field took Mach number,angles of attack,altitudes as variables respectively.First is to simulate the turret and small-scale turbulent field.ICEM was used to establish a turret model and divide the turbulent field into structured mesh.Then Large Eddy Simulation(LES)was used to simulate flow fields with different Mach number,different altitudes and different angles of attack after importing the turbulent field into ANSYS Fluent.Among all turbulent fields,there were 13 small-scale turbulent fields and 40 sampled turret turbulent fields.Second is to simulate the optical filed.2nd-order compact differences were used to solve the Helnholtz differential equation for inhomogeneous medium and along optical path 4th-order Runge-Kutta method was taken to calculate the amplitude and the optical path difference(OPD)of light beams which just got out of aerodynamic area,and all of these optical computations were done by Mathematica.Last is to evaluate beams' quality after they propagating through turbulent field.Strehl ratio(SR)and imaging displacement(referred to as displacement)were used to evaluate beams' phase and amplitude stability respectively.The simulations show:in the same turbulent field,LG beams have better phase stability than Gaussian beam and in most cases have worse amplitude stability than Gaussian beam and LG beam which has more topological charges has worse amplitude stability.In turret turbulent fields,the displacement of LG beams is more sensitive to the changes of attack angles and altitudes than that of Gaussian beam;when attack angle is large or Mach number is low or altitude is low,the kinds of light beams have little impact on beams' SR.In small-scale turbulent fields,when flying conditions are same,LG beam which has more topological charges has larger SR;there is and there only is LI beam has better amplitude stability than Gaussian beam;if computational conditions or experimental conditions are not good enough,the simulation of light through small-scale turbulent field can partly reveal the minutiae of aero-optical effects of light beam propagating through real scale turbulent field.