Amplification System Of High Average Power Pulsed Fiber Laser

In recent years,with the increasing demand for environmental friendliness in the manufacturing sector,high-power pulsed fiber laser systems with high average power,high pulse energy and high peak power,and widely adjustable pulse duration and repetition frequency,while maintaining all the advantages inherent in fiber laser systems,have become clean light sources that can replace traditional cleaning applications.However,the power boost of high-power pulsed lasers is limited by nonlinearity.In addition,the average and peak power increases of all-fiber structured pulsed laser amplification systems are also limited by the high difficulty of manufacturing large core diameter fibers,high fusion loss of large diameter fibers,and the lack of manufacturing processes that can withstand high power pump couplers and laser combiners.This thesis discusses and investigates the above limitations,and the main research results and conclusions obtained are as follows:In this paper,we propose a dual acousto-optic seed structure with low-speed acousto-optic and high-speed acousto-optic interactions to achieve the regulation of repetition frequency,pulse shape and pulse delay of the optical system.The dual-acoustic structure can keep the pulse shape as Gaussian or Gaussian-like waveform for high-energy cleaning applications,while effectively optimizing the pulse shape and keeping the seed power at a high energy level.The results show that the optical system structure of the dual-acoustic design is more concise and helps achieve laser output with both high average and high peak power.In this paper,a high-power pulsed laser system based on single-cavity output is studied.Passive fibers with core diameters of 100～300μm and ytterbium-doped fibers are designed and prepared,large-diameter fiber cutting and fusion techniques used in high-power pulsed fiber systems are discussed,the characteristics and key parameters of key devices such as fiber mode matchers,fiber pump couplers,fiber combiners and cladding optical strippers are discussed and analyzed,and their operational reliability in high-power pulsed amplification systems is experimentally designed and verified.Based on the self-developed key devices and pulse modulation technology,a Q-tuned resonant cavity is used to obtain a pulsed seed laser,and a dual acousto-optical modulation system is used to achieve pulse frequency control and pulse waveform modulation.In this paper,two types of large-diameter Yb-doped fibers(200μm and 300μm)with self-developed core size were used as the gain fibers of the main amplification stage for the first time,and the laser output with an average power of 504 W,a single pulse energy of 50.4 m J and a peak power of 345.2 k W was obtained in a 200μm all-fiber structured amplification system.Then,based on the 200μm single module amplification optical path,the seed source design was optimized in the 300μm all-fiber structure to enhance the power of the seed laser;the pulse waveform control system was designed to control the pulse shape and adjust the repetition frequency of the system;the forward pumping method was changed to reverse pumping to shorten the fiber length;the large core fiber was used as the gain fiber of the pre-amplification stage to enhance the power of the signal laser entering the main amplification stage.signal laser power into the main amplifier stage.The output laser power is 512 W,the single pulse energy is 51.2 m J,and the peak power is more than 1 MW,which is a pulsed laser with both high average power and high peak power.The maximum cleaning efficiency of 4.32 m2/h was obtained with the 300μm laser amplification system at a setting of～500 W average power and～340 k W peak power in the case of rusted plates without ablation and re-oxidation of the substrate after laser cleaning.Due to the high peak power density of fiber lasers,it is difficult to achieve extremely high-power levels of pulsed fiber laser output from a single pulsed laser module.The combined beam output of multiple single-module pulsed lasers through a fiber combiner can produce higher laser power output,and the power output produced is proportional to the number of lasers combined.Therefore,based on the results of single-cavity laser amplifiers,a combined beam output system for high-power nanosecond fiber lasers is also investigated in this paper.Based on a dual acousto-optic modulation scheme,a pulsed laser output of more than 3 k W was achieved by combining three laser modules with an average power of 1 k W using a homemade high-power fiber combiner and controlling the pulse recombination rate by controlling the design of the pulse delay system.The highest cleaning efficiency of 21.6 m~2/h was achieved at a laser repetition rate of 100 k Hz for cleaning rusted surfaces.