200W Nanosecond Pulsed Fiber Laser Based On MOPA Structure

As an important product of industrial 3D manufacturing,high power fiber laser has become an indispensable component in material addition processing.Pulsed fiber lasers are the focus of current research in rate fiber lasers.Pulsed Master Oscillation Power Amplified Fiber Laser(MOPA)has broad prospects in the fields of laser processing,medical and health,weapon manufacturing and space optical communication due to its good beam quality,large single pulse energy and high average power.At present,there is still room for further research on the output optical power and pulse energy of MOPA fiber laser.In the process of laser amplification,the spontaneous emission effect(ASE),non-linear effect and thermal effect produced by fiber laser are all the reasons that hinder the development of pulsed fiber laser.Therefore,based on the above research background,this topic carries out related research on MOPA pulsed fiber laser system.Firstly,we make a laser.Then we study the spontaneous emission and non-linear effects in the amplification process of the fiber laser,and how to suppress these effects so as to improve the average power.Finally,the peak power and beam quality of the system are improved,and nanosecond pulsed laser is output.The main work of this paper is as follows:(1)The introduction firstly introduces the background of the research on fiber laser and the significance of the research on 200 W nanosecond pulsed fiber laser.The related literatures about nanosecond pulsed fiber lasers at home and abroad are studied,and how to generate nanosecond pulses in fiber lasers is summarized.(2)Chapter 2 mainly elaborates on the relevant knowledge of pulsed fiber lasers.Firstly,the basic theory of fiber lasers is introduced.Secondly,the theory of traveling wave amplification,the mode characteristics of gain fiber,the theory of non-linear effect and other factors affecting fiber lasers are introduced.(3)In Chapter 3,the key technologies of MOPA nanosecond pulsed fiber laser are described in detail.In this part,firstly,the working principle of pulsed fiber laser is introduced,and the pump coupling technology in fiber laser is discussed.Then,the double cladding fiber commonly used in high power fiber laser is described.Finally,the research status of fiber bunching technology is introduced.(4)The last part of the experiment is the experimental design of a high power nanosecond pulsed fiber laser with MOPA structure.The structure of seed source and two-stage cascade amplification is adopted.The laser consists of a modulated semiconductor laser seed source,a single mode single clad Ytterbium-doped fiber amplifier(10 ?m/125 ?m)and a two-stage large mode area Ytterbium-doped fiber(30 ?m/250 ?m).The spectral center wavelength of the semiconductor laser seed source is 1064 nm.After modulation,the laser pulse width can be tuned,ranging from 10 ns to 350 ns,and the repetition frequency can be tuned in the range of 200 kHz to 1500 kHz.When the repetition rate of laser seed source modulation is 200 kHz and the pulse width is 350 ns,the seed light is amplified by a single clad Ytterbium-doped fiber amplifier at first stage,and the output is 680 mW after the second stage amplification,and 201.7 W after the second stage amplification.After amplification,there is no obvious phenomenon of amplified spontaneous emission in the spectrum.