| High-power,high-energy solid-state lasers(HP/HES SL)offer a wide range of applications in national security,industrial processing,major equipment,scientific research,facilities,medical and health,etc.The pursuits of higher efficiency,higher power,higher beam quality,higher reliability,more compact system structure,and multifunctional operation mode have been the main goals and trends of HP/HESSL research and development.Whether it is a HPSSL system for fusion energy and high-energy-density physics research,or a HESSL system for military applications such as laser weapons,how to effectively control the thermal effects in the laser system and ensure the module,general,compactness and scaling ability of the laser system have become the major problems to be solved in the development of HP/HESSL.We systematically analyze the limits for gain,heat load,power load and fluence load.We also analyze the influence factors for these four limits and semi-quantitatively provide the design range of the high peak power laser system.This part is mainly described in Chapter 2.Based on the characteristics of pumping and energy storage,as well as the mechanism,influence and control of heat effect in the solid laser gain media,combined with the requirements of repetition rate and continuous operation modes,we propose a novel concept of "laser gain chip"(LGC),where the travel directions of the pumping field,cooling field and the laser field are orthogonal to each other.The LGC can be the "benchmark" module of the gain unit for the advanced HE/HPSSL system in the future.LGC has a high degree of functional integration.Firstly,its aperture can be adjusted in some degrees;secondly,gain extension can be obtained by increasing the LGC in the longitudinal direction.In this paper,we systematically analyze the basic and potential characteristics,as well as technical limits of the conceptual model of LGC.The gain medium of the LGC has a slab-shaped geometry,where double edge pumping,fluid cooling of two optical interfaces,and laser free transmission and amplification have been employed.In addition,the travel directions of the laser,cooling liquid and pumping light are orthogonal related to the gain medium in space.This paper provides the research framework of LGC,which establishes the foundation for specific applications,structural design and system integration of LGC.Furthermore,we propose the high-brightness pumping for LGC based on the band-shaped waveguide.We analyze the characteristics of orthogonality of the three fields and transvers grading doping for the LGC.These characteristics can ensure longitudinal gain extension and modular design for LGC when it applies in the future laser system.This part is mainly described in Chapter 3.We systematically studied the influence of the edge-pumping configuration on the gain uniformity of LGC.A new method based on gain media with transverse gradient doping is proposed.To our knowledge,this is the first time that the analytical and numerical models of the two kinds of activated ions(four-level and quasi-three-level)to achieve uniform transverse gain(UTG)are derived under the condition of bidirectional edge pumping.This method is extended to continuous-,long-and short-pulse pumping conditions.With the three-dimensional energy storage model based on ray tracing,we demonstrated the feasibility of one-dimensional gradient doping method in the case of pulsed pumping.Taking Yb:YAG as an example,the results show that the gain uniformity with short-pulse pumping is better than that of the long-pulse pumping.In addition,results show that short-pulse pumping not only reduces the loss of spontaneous emission,but also reduces the loss of amplified spontaneous emission as well as the heat load in the laser system.This part is mainly described in Chapter 4.The effects of fluid-cooled the optical interface of the LGC are systematically studied,which focus on the influences of the thermal effect and the fluid field on the laser field.Based on the thermodynamics and flow-solid coupling model,we analyze the heat dissipation capacity for the gas cooling method under different cooling conditions(temperature and flow rate)by the finite element analysis method.Taking Yb:YAG as an example,we quantitatively give the thermal-induced wavefront distortion and deviated loss in LGC under Helium cooling.Since the laser will travel through the gas field,we analyze the effect of the gas flow field on laser wavefront distortion.The results show that the flow field of the gas has a relative small effect on the wavefront distortion of the laser beam.In addition,we preliminarily discussed the heat dissipation of liquid cooling.This part is mainly described in Chapter 5.We systematically studied the relationship between LGC and laser system.Aiming at the basic requirements of the output characteristics of the pulsed and repetition rate operation laser system,the analytical and numerical models of the pulse temporal overlap are established for the first time,where the loss is taken into account.The influences of the pulse overlap effect on the laser energy extraction and the pulse-shape distortion are discussed.The theoretical model of laser pulse amplification is of great importance to the design of compact laser amplifiers.This part is mainly described in Chapter 6.Based on the novel concept of three-field orthogonal LGC,we designed and developed kilo-joule class nanosecond solid(Yb:YAG)laser system.Compared with the traditional pumping technology,a significant increase of the pump brightness for LGC has been achieved due to the edge pumping configuration,which ensures a relatively short pulse pumping and higher storage efficiency.The transvers gain uniformity of LGC is greatly improved by using transvers gradient doping,and the gain modulation(peak-to-average)is about 1.017,which satisfies the requirement of the gain uniformity of the fusion energy driver.With the multi-pass amplification technology the laser system can deliver about 1.1 kJ pulses with optical-to-optical efficiency of 43.3%.This amplifier can provide substantially technical supports for the feasibility of the pumping source for advanced radiation system and future fusion energy driver.This part is mainly described in Chapter 6. |
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