Pulse Modulation Mechanism And Experimental Study On Erbium-doped Fluoride Fiber Laser

Mid-infrared laser source can cover most of the absorption windows of gas,liquid and solid molecules,and has important applications in atmospheric remote sensing,environmental monitoring,lidar and other fields.Among them,the mid-infrared fiber laser has the advantages of high power,high beam quality,high efficiency,and compact system,and has become a research hotspot in mid-infrared laser technology.At present,with the improvement of fiber manufacturing technology and the maturity of pump source technology,high-power mid-infrared fiber lasers are developing rapidly.However,compared to visible light and near-infrared bands,low-loss,high-efficiency mid-infrared materials and optoelectronic components are scarce,which limits the improvement of mid-infrared laser performance.Recently,researchers have obtained pulsed mid-infrared fiber laser output through active and passive method.Based on the broadband absorption characteristics of low-dimensional materials such as graphene and graphene-like materials,the pulsed mid-infrared fiber laser output has been obtained experimentally.Based on active modulation methods such as acousto-optic switches,the modulation capabilities have been demonstrated.However,with the application requirements of high-power,high-energy,and stable mid-infrared lasers,the performance indicators of mid-infrared fiber laser light sources that have been reported so far need to be improved urgently.The thesis mainly focuses on the Q-switched 3?m-band fiber lasers by exploring passively Q-switching via novel passive saturable absorbers and actively Q-switching methods based on acousto-optic switches,respectively.The specific contents are as follows:(1)Based on the ternary chalcogenide compound Ta₂Ni S₅ saturable absorber,the stable mid-infrared pulsed fiber laser output has been obtained.The layered Ta₂Ni S₅saturable absorber was successfully prepared by liquid phase separation(LPE)and the nonlinear optical response of Ta₂Ni S₅ was measured based on the Z-scan platform.The modulation depth and saturation intensity obtained were 35.6%and32.2 GW/cm²,respectively.The layered Ta₂Ni S₅ saturable absorber was applied to the mid-infrared laser cavity,and a stable pulse trains with a repetition rate ranging from 18.2 k Hz to 102 k Hz was obtained.The average output power and pulse width were obtained at the maximum pump power of 860 m W,which are 168 m W and 1.20?s respectively.The signal-to-noise ratio of the Q-switched pulse sequence was as high as 42.6 d B,which is currently the highest value of two-dimensional materials in the mid-infrared range.It proves the superiority of Ta₂Ni S₅ and provides guidance for the exploration of mid-infrared saturable absorbers.(2)The actively Q-switched mid-infrared fiber laser based on acousto-optic modulator has been demonstrated successfully.By introducing the acousto-optic modulator to the mid-infrared fiber laser cavity,the pulse laser output with stable and tunable repetition rate was successfully realized.Under the maximum pump power of4.1 W,a stable pulse sequence with tunable repetition rate ranging from 40 k Hz to 90k Hz is realized.The corresponding laser center wavelength is 2.792?m,and the peak power obtained is 103.7 W,and the pulse width is 148 ns.In addition,the influence of pump power,driving signal duty cycle,and repetition rate on the characteristics of output pulses is analyzed.Furthermore,we also analyzed the reasons of secondary pulses,and proposed solutions to the phenomena.