The Investigation Of High Power Fiber Laser Oscillator And Its Array Atmospheric Transmission

Having the advantages of simple and compact structure,high conversion efficiency and brightness,high power fiber laser oscillators are widely adopted as laser flexible sources in the applications of industrial manufacture and military defense.Due to the limitation of thermal and nonlinear effects,the power of separate fiber is far from meeting the requirements.Using beam combining technique to fabricate a high-power fiber laser system has many attractive characteristics,including higher final output power,which can maintain good beam quality simultaneously,thus facilitating their potential applications in various fields including high-power fiber laser application systems.Therefore,it is of great importance to develop incoherent beam combining composed by high-power monolithic fiber laser oscillators with good beam quality.In this dissertation,through investigation of the high-power monolithic fiber laser oscillators and incoherent beam combining has been demonstrated,which includes:The numerical and experimental investigation about effectively mitigating the SRS and TMI effects has been presented.The effective methods and techniques of engineering the monolithic fiber laser oscillator are put forward and discussed,including overall scheme improvement,optical fiber fusion process innovation,structure compact improvement and experimental investigation of SRS/TMI effects.By using these modified fabrication technique,high-power fiber laser oscillator based on wavelengthlocked pump and co mmercial ytterbium-doped fiber with core/inner cladding diameter of 25/400 μm has been engineered for the first time.The latest engineering prototype,with the key technical indexes such as output power and beam quality having reached the international advanced level,is pretty smaller in volume and weight than the previous generation of the same power prototype.The influence of the transmission mode and effect of coherent/incoherent beam combining,the theoretical analysis,the simulation results as well as the control structure between them,on the long-distance transmission in turbulent atmosphere,has been analyzed.In contrast,incoherent beam combining is an even better choice,solving the problem of easy-to-use ability.The numerical and experimental investigation of the beam spot shape after 7-channel Gaussian beams reaches the target is carried out,focusing on the influence of the phase difference of the single beam.In this paper some useful technical schemes,by means of which the incoherent beam combining can be achieved,have been su mmarized.Adopting high duty cycle honeycomb modular design,we realized the spatial incoherent beam combining,where the far-field light spot is not larger than the single largest light spot.It can Realize longtime high-precision beam synthesis and reduce the flicker of the spot on the target,in which the high precision real-time active closed-loop synthesis control makes the synthetic far-field spot close to the single-channel far-field spot size.When the singlechannel equivalent emission aperture is close to the atmospheric coherence length,the emission aperture can be utilized to the maximum extent.High-precision,real-time adjustment of a single beam,closed-loop work for a long time,even if the multi-channel laser fails,the remaining beams can still work normally.Systematically theoretical and experimental studies indicate that,with high robustness and adaptability,spatial beam combining is a cost-effective solution adapting to the laser level and emission aperture shape to the greatest extent.