| Fiber laser has been a focus in the laser research field for years and has attracted a variety of applications in military,scientific and industrial domain.The power reflection from materials during cutting or welding could cause severe damage to the fiber laser system,particularly for those in MOPA(master oscillator power amplifier)structure.It is important to develop related technology to reduce the risk of damage caused by back reflection.As technology updates and demand increases,antireflection is not the only research target.Only fiber lasers with high output power,high efficiency and high beam quality at the same time are able to meet the higher demand of scientific research and application.In order to obtain high efficiency and antireflection feature at the same time,a new fiber laser architecture,with integrated oscillator and amplifier structure,is proposed in this thesis.The model was established,which can analyze the main factors that will affect performance of laser.According to this model,those main parameters such as the length of gain fiber,pumping methods and cavity reflectivity were optimized,and the transmission and amplification of back reflection were also analyzed.?.The common ideas and methods to reduce the risk of damage caused by back reflection were introduced.Fiber lasers with oscillator-only structure are widely used in material processing industry for the higher tolerance to the reflected light.Despite all this,the optical conversion efficiency of single oscillator is normally not competitive with MOPA architecture.Combining the advantages above two,a new fiber laser architecture with integrated oscillator and amplifier structure is proposed.?.Based on laser rate equations,the model of fiber laser architecture with integrated oscillator and amplifier structure was established,which considered influences caused by central wavelength,pumping wavelength,pumping methods,length of gain fiber,cavity reflectivity,and back reflection.?.Fiber laser with different proportions of length of gain fiber and different proportions of forward and backward pump power was simulated and compared using the theoretical model,and results of which showed that the anti-reflection threshold declined with output power of OSC,and the higher power of OSC,the higher anti-reflection threshold.The output power of OSC could be increased by increasing the proportions of gain fiber in OSC and proportions of forward pump power.However,the change of efficiency and anti-reflection threshold were negatively related.At last,two solutions were proposed:a)Long cavity structure was proposed to achieve higher anti-reflection threshold with simulation result of O-O efficiency78.0%and power of reflected light increased by 2.1 times.b)Short cavity structure was proposed to achieve higher efficiency with simulation result of O-O efficiency 84.2%and power of reflected light increased by 11.2 times.The above results provided standards for the experimental research.?.The design had been verified by experimentally researching both of two solutions:a)Maximum power 1834 W cw laser was achieved by long cavity structure at a pump power of 2414 W.The O-O efficiency was 76.5%,the slope efficiency was 76%,and the beam quality was M2=1.57.b)Maximum power 2031 W cw laser was achieved by short cavity structure at a pump power of 2489 W.The O-O efficiency was 81.6%,the slope efficiency was 82.7%,and the beam quality was M2=1.38.Output light of both fiber lasers illuminated at an aluminium plate in front of the QBH vertically to validate the antireflection feature of each structure.The results indicated that the long cavity structure all-fiber laser system and the short cavity structure all-fiber laser system were able to keep steady under high reflection. |
PDF Full Text Request