Study On Beam Propagation And Control Optimization In A Relay Mirror System

The relay mirror technology is an important new laser system combat concept thathas unique application in military field, which has been under extensive research inrecent years. Begin with the basic concept, contents including theory of beampropagation in a relay mirror system, the feasibility of a relay mirror system, powercoupling efficiency of a relay mirror system and the methods used to improve uplinkpower coupling efficiency, influences induced by the two adaptive istallations areinvestigated in theory, simulation and experiment in this thesis.First, theory of beam propagation in a relay mirror system and the feasibility of arelay mirror system are investigated in theory and experiment. Based on the previousresearches on the relay mirror technology, components of a relay mirror system isanalyzed, the optimal mode of beam uplink propagation is analyzed with the emphasison the damage performance at the target. Based on the optimal mode, theory of beampropagation in a relay mirror system is analyzed, the equivalent Fresnel number of beampropagation in a relay mirror system under vacuum and turbulence conditions, therelations between the maximum beam intensity at the target and the equivalent Fresnelnumber are both ratiocinated in detail. The conditions in which a relay mirror system isfeasible is analyzed, the method used to compute the advantage scope of a relay mirrorsystem is illuminated. As examples, the advantage scopes of relay mirror systems withspace-based laser, airborne laser and ground-based laser are simulated. In the laboratory,a reduced-scale experimental installation is established with the same Fresnel number ofbeam propagation in a relay mirror system with1.064μm laser source,1.2m-diametertelescopes,30km uplink propagation distance and10km downlink propagation distance.With the experimental installation, the reduced-scale experiment is carried out. Thetheoretical results and the experimental results show that the relay mirror system canimprove the laser damage performance to the forane target and extend the laser’s range.Second, influences to the relay mirror system damage effect induced by the twoadaptive optics istallations are investigated in theory. According to the different workingconditions and different uses, styles of the two adaptive optics istallations used in arelay mirror system are analyzed with the characteristics and styles of the adaptiveoptics used in nowadays. We get that the adaptive optics istallation locates at the sourceshould use the conjugacy based adaptive optics, the adaptive optics istallation locates atthe platform should use the optimization algorithm based adaptive optics. Based on themodel of a ground-based laser relay mirror system under the Hufnagel-Valley5/7turbulent model condition and with the parameters as:25km target height and30kmplatform height, performances of the relay mirror system under different precisions ofthe adaptive optics istallations are simulated. The results show that proportion of power in bucket with diffraction limit radius is61.44％under the closed-loop and idealconditions, which is3.6times of the value under the open-loop.Then, power coupling efficiency of beam uplink propagation in a relay mirrorsystem and methods used to improve the uplink power coupling efficiency areinvestigated in theory and experiment. In theory, power coupling efficiency of beamuplink propagation in a relay mirror system is simulated, theories of three methods usedto improve the uplink power coupling efficiency including beam shaping, coherentbeams combination and vortex beams are analyzed, and performances of the abovemethods are simulated. The theoretical results show that uplink power couplingefficiency of the relay mirror system is84.46％, power coupling efficency is improvedfrom84.46％to99.73％by beam shaping; power coupling efficency is improved from84.46％to95.02％by coherent beams combination; power coupling efficency isimproved from84.46％to98.04％by using vortex source. In experiment, areduced-scale experimental installation is established, and the experiment of detectinguplink power coupling efficiency of the relay mirror system is carried out. By using twoliquid crystal spatial light modulators, the experiments of detecting uplink powercoupling efficiencies of the relay mirror system with beam shaping and vortex sourceare carried out. The experimental results show that uplink power coupling efficiency ofthe relay mirror system is71.89％, uplink power coupling efficency is improved from71.89％to87.88％, proportion of power in5pixelsbucket （32.25μm radius）isimproved from44.52％to52.78％by beam shaping; uplink power coupling efficencyis improved from71.89％to90.60％by using vortex source.At last, performances of beam control optimizations in a relay mirror system areinvestigated in theory. Taking beam shaping as an example, performances of a30km-height relay mirror system with different precisions adaptive optics istallations aresimulated under the Hufnagel-Valley5/7turbulent model.The results of this dissertation may provide some references for the design and thedevelopment of the relay mirror system, the three methods proposed in the paper thatused to improve uplink power coupling efficiency of the relay mirror system can beused in laser systems including laser communication systems, laser data transmittionsystems and so on.