Research On High Power Nanosecond Pulse Fiber Laser Based On MOPA Structure

High-power pulsed fiber lasers have the characteristics of high single pulse energy,good beam quality,high conversion efficiency,and low thermal efficiency.They are widely used in many fields such as industrial processing,medical care,military weapons,and precision measurement.In the field of laser processing,due to the presence of unsmooth pulses,it is difficult to obtain ideal pulse waveforms,which reduces the quality of the output laser,affects the processing effect,and reduces the practicality of laser processing.Output pulse smoothness is an important indicator of pulsed fiber lasers.Therefore,this paper proposes a method and structure for controlling the pulse non-smoothness.The output characteristics of pulsed fiber lasers with asymmetric cavities and symmetric cavity seed sources are studied,and a high-power pulsed fiber laser is constructed.The specific work of the paper is as follows:1.The related principles of high-power nanosecond fiber lasers are studied.The structure principle of the fiber laser is described and the key technologies of the pulsed fiber laser are analyzed.The principle of the acousto-optic Q-switched fiber laser and the MOPA structure are studied in detail.2.Based on the basic theory of asymmetric cavity,an asymmetric cavity seed source experimental system was set up,the output characteristics of the system were studied,and the output power,repetition frequency,pulse width,pulse waveform,laser spectrum and other parameters of the seed source were tested.The maximum output power is 1.61 W,the center wavelength is 1063.93 nm,the 3dB bandwidth is 0.12 nm,the minimum pulse width is 61 ns,and the repetition frequency is adjustable from 10 KHz to 80 KHz.Among them,the emphasis has been placed on the phenomenon that the repetition frequency of the seed source output pulse and the Q-switching repetition frequency are not equal,and the reasons for the occurrence of unequal pulses of energy are analyzed.A method to control the multi-peak phenomenon of the pulse is proposed.By adjusting the system power parameters such as system pump power,Q-switch repetition frequency,turn-on time,and rise time,the characteristics and laws of the system were analyzed,and the number of multi-peak pulses was successfully reduced.This improved the smoothness of the output pulse of the asymmetric cavity seed source system.But there is still the problem of pulse non-smoothness.3.In order to solve the problem of output smoothness of the seed source system,based on the theory of symmetric cavity,a symmetry cavity seed source experimental system was proposed and built,the output characteristics of the system were studied,and the seed source output power,repetition frequency,and pulse width were tested.Parameters such as pulse waveform,laser spectrum and other parameters obtained a smooth pulse sequence with a maximum output power of 0.59 W,a center wavelength of 1063.98 nm,a 3dB bandwidth of 0.14 nm,a minimum pulse width of 58 ns,and a repetition rate of 10KHz-80 KHz.Among them,the reason for the appearance of "chaotic" pulses was studied emphatically.The effects of unequal pump power at both ends of the system on the smoothness of the output pulse were compared and analyzed,and the problem of unsmoothed output pulses was solved.4.In order to increase the output power of the laser,a high power nanosecond pulsed fiber laser was built using the MOPA structure.The seed source adopts a symmetric cavity structure,and the amplifier stage adopts a second-stage amplification method.The output power,pulse width,laser spectrum,and pulse waveform of the first and second stage amplifiers are respectively tested.After integrated integration,the average power is finally obtained at 30.3 W.Smooth pulsed laser is output.