Research On Key Technologies Of High Power And High Energy Fiber Laser Light Field Regulation

High power and high energy fiber laser has wide application prospects in key fields such as military and national defense,science research,medical,industrial process,etc.due to its high efficiency,high reliability,and good capability for light field control.Especially,the designable and controllable properties of fiber material and structure provide essential technical methods to precisely control the output optical field in universal-domains(including time domain,space domain and frequency domain)of high power and high energy laser system which aims to many significant applications,as well as establish necessary technical foundation for improving the quality of output beam.As for the high peak power fiber laser system,obtaining the pulse which is strict single transverse mode,high contrast and optical spectrum precisely controllable by precisely regulate and control in universal-domains on the conditions of high peak power is one of the based requirements of high quality output.As for the high average power fiber laser system,high quality output requires rigorous mode control to enlarge the effective mode area and obtain high stable,high purity,transmissible laser mode,hence improves output scale and beam quality of the system,and also satisfies strict transmission requirements.It is hard to further improve the output scale for the traditional cylindrical symmetry and solid fiber which is limited by nonlinear,thermal effect,optical damage,modulation instability and other factors.Therefore,this paper aims to effectively improve output scale of high power and high energy fiber laser system based on single fiber and single mode and researches on key points of optical field control technologies related to high power and high energy fiber laser.This paper mainly includes the following three sections:1.Theories,limiting conditions and design criteria of high power and high energy fiber laser.This paper systematically arranges basic theories for high power and high energy fiber laser.Five limiting conditions(i.e.gain scale limiting,mode-selection limiting,thermal limiting,power limiting and stored energy limiting)which limit the improvements for high power and high energy fiber laser system based on single fiber and single mode are analyzed and studied.The individual main mechanisms,basic rules and affected factors are investigated and cleared.The for physical design methods of high power and high energy fiber laser system based on the above five limiting conditions and eigen parameters are proposed.This paper also presents the basic elements which apply the above methods to high peak power and high average power fiber laser system.This section is mainly described in the second chapter.2.Precisely regulate and control technology in universal domains of high peak power fiber laser system.Aiming to the two basic requirements that "no jitter" output of extreme-multi-beam ns-level seed source in ICF mega-Joule level laser facility and precisely regulate and control in time,space and frequency domains,the time domain and frequency domain evolution characteristics of frequency modulated pulse during transmission and amplification in high peak power fiber laser system are theoretical analyzed and the key parameters to optimized design of single beam high power fiber seed source are obtained.The design thought of "dense time division multiplex,beam after bundle selected" is proposed.The design and related experimental demonstrations of mJ level extreme multi-beam fiber seed source system are completed.By employing with the key technologies such as high contrast pulse generation,waveguide phase modulation with compound modulated frequencies,suppression of FM-to-AM and single transverse mode large mode area fiber amplifiers,this paper experimentally demonstrates single transverse mode high power fiber seed source with pulse energy of 1.02 mJ@5ns,spectral width of 0.3nm,better than 500:1 pulse contrast,long-term stabilities of FM-to-AM less than 5.2%in 3 hours,which settles solid technology basis for engineering design and manufacture with extreme-multi-beam high power output and strong laser pulse control ability.This part is mainly described in the third,fourth and fifth chapter.3.Preliminary research on general technical route to 100kW level single fiber high quality and high energy fiber laser.According to the issue of beam-target coupling and long distance transmission,this paper proposes concept as "ring-band" fiber laser and "ring-band super uniform mode" fiber with larger than 10,000?m2 fundamental mode area.The effects and rules on mode distribution resulted by the inner ring radius and ring thickness of ring-like super uniform mode fiber are theoretical analyzed.Meanwhile it proves that mode numbers increase with annual mode area increasing;however there exist super large uniform fundamental mode.Besides,the conversion property between annular beam and ring-band beam is studied.The consequence indicates that the ring-band beam could be conversed to annular beam which is suitable long distance transmission with high efficiency through appropriately designing beam conversion system.The above research achievements provide necessary scientific basis to confirm the general technical route to 100kW level single fiber high quality and high energy fiber laser.This section is described in the sixth chapter.