Research On Temporal Pulse Shaping Technology Of Ytterbium-doped MOPA Fiber Laser

The main oscillation power amplification(MOPA)scheme is the most common and effective method to obtain high-energy,high-beam quality laser output.However,due to the occurrence of gain saturation within the gain medium,MOPA system is often bothered by the fact of a largely deformed output temporal pulse shape which deviates from that of the input seeding laser,thus resulting into an uncontrollable output pulse waveform.In the fields such as laser processing,laser medicine and laser communication,specific temporal pulse shapes are always required to improve the work efficiency and effectiveness.For this reason,researchers have proposed MOPA temporal pulse shaping technology aimed at achieving target pulse shape output.Considering that optical fiber laser is one of the main development directions in laser applications in the future,this dissertation studies and mainly focuses on the research and simulation of Ytterbium-doped fiber MOPA.The main contents involve the following works.(1)The theoretical model of Ytterbium-doped fiber amplifier is studied and simulated.A one-dimensional model of ytterbium-doped fiber amplifier is established,and the numerical simulation of its steady-state performance is performed with the tool software of Matlab.The influences of different parameters,such as pump power,signal intensity,doping concentration,fiber length and input beam quality,on the output power of the amplifier are studied through numerical simulation.(2)A theoretical model of laser pulse amplification in the forward pumpling scheme is established.The temporal pulse shape amplified by a fiber amplifier is obtained through numerical simulation,with the output pulse shape of a fiber MOPA system is also measured in the experiments.With the theoretical model,the pulse gain is studied and the relationship between the degree of deformation of the output pulse shape and the parameters such as pulse width,signal laser power,fiber length and incident angle are also explored.(3)For the reverse problem of temporal shaping process of laser pulse amplification,the formula of the pre-compensation laser pulse amplification is deduced and the pre-compensated pulse shape is obtained through Matlab simulation.A correction method considering the optical fiber transmission path is proposed,and then the relevant correction pre-compensation pulse formula is also derived.It is noticed that with a higher doping concentration or a larger optical fiber numerical aperture,the transmission pathway of the laser beam within optical fiber has a significant influence on the pulse shape deformation.Besides,when the laser beam experiences a longer optical length in the fiber,a greater impact is also expected in the output pulse waveform.In these cases,the correction formula can obtain the pre-compensated input pulse shape more accurately.This dissertation systematically studies the temporal pulse shaping technology based on Ytterbium-doped fiber MOPA.The theoretical model of ytterbium-doped MOPA,the dynamic process of pulse amplification and the pre-compensation are analyzed and numerically studied respectively.This results in a more clear picture on the dynamic process of Ytterbium-doped fiber MOPA amplification and the influences of important parameters,which may help the future relevant studies.