Ytterbium Doped Fiber Laser Technology And Application Based On Nonlinear Polarization Rotation Mode Locking

Ultrashort pulse fiber lasers have been widely used in industrial manufacture,medical diagnosis,military confrontation and scientific research because of their narrow pulse width,high peak power,compact structure and system stability.Passively mode-locked fiber lasers are a major means of obtaining ultrashort pulses,so the development of high-performance passively mode-locked fiber lasers has good research significance and practical value.In this thesis,we have studied mode-locked Yb-doped fiber lasers and amplifiers based on Non-linear Polarization Rotation(NPR)technology theoretically and experimentally.Using the Dispersive Fourier Transformation(DFT)technique,the transient processes of the creation and disappearance of the mode-locked pulses are investigated.A two-photon fluorescence imaging system has been built using the NPR mode-locked Yb-doped fiber laser and amplifier as the light source.The main contents of the thesis are as follows:1.The research significance and types of passively mode-locked fiber lasers are briefly described,mainly introducing the research progress and current status of NPR mode-locked ytterbium-doped fiber lasers based on NPR;the relevant concepts of dispersive Fourier transform technology and the current status of domestic and international research on two-photon fluorescence microscopy imaging are introduced.2.The advantages of the Yb-doped fiber laser are described in terms of the energy level structure,emission and absorption spectral lines of the Yb ion.A mathematical model of the NPR mode-locked Yb-doped fiber laser is established by means of the nonlinear Schr?dinger equation for pulse transport in the fiber,and the effects of parameters such as initial pulse width and energy,laser cavity length,gain and filter bandwidth on the output pulse characteristics are simulated theoretically.3.An NPR mode-locked ytterbium-doped fiber laser was built and various modelocked pulse states including dissipative solitons,noise-like pulses and soliton molecules were obtained by modulating the intracavity dispersion.The seed light was amplified and compressed outside the cavity using a fiber MOPA system to obtain a noise-like pulse output with a peak power of 24 k W.4.A DFT system was built,and the image distortion phenomenon was corrected and digital filtering was implemented by writing a data processing program.The system was used to study the creation and disappearance of mode-locked pulses,and the invisible soliton pulsation phenomenon was observed inside the laser.5.A two-photon fluorescence imaging system was built on the basis of a homemade mode-locked ytterbium-doped fiber laser.The basic principles of two-photon fluorescence absorption and excitation were introduced,and the relationship between fluorescence power and peak power of excitation light was discussed.Two-photon excitation of rhodamine B was observed experimentally.