Mid-infrared New Type Saturable Absorber Q-switched And Gain-modulated Fiber Laser

The mid-infrared pulsed fiber laser has a wide range of application prospects in fields such as biomedicine,space remote sensing,industrial processing,and national defense military,due to its outstanding advantages such as good beam quality,good heat dissipation,and good monochromaticity.Based on the Ho³⁺and Pr³⁺co-doped fluoride fibers,this paper studies the characteristics of mid-infrared passively Q-switched pulsed fiber lasers,what's more,three types of materials were used as true saturable absorbers,and passive Q-switched pulsed laser was first obtained in the 3?m band respectively.In addition,a mid-infrared gain-modulated pulsed fiber laser was constructed based on Er³⁺-doped fluoride fibers,and the mechanism of the gain-modulated pulsed laser was studied and analyzed comprehensively.The main work of this paper can be divided into the following points:1.Based on Ho³⁺-doped fluoride fiber,Ho³⁺/Pr³⁺co-doped fluoride fiber and Er³⁺-doped fluoride fiber,the related equations such as rate equation,power coupling equation are established respectively,and on the basis of this,passively Q-switched laser model based on real saturable absorbers is established.Through the numerical simulation of the established model,the influence of fiber length and fiber doping concentration on the performance of the laser is obtained.In addition,the trend of passively Q-switched pulse laser characteristics with the pump power is also obtained.Through relevant theoretical analysis,we have optimized the fiber length and doping concentration used in the experiment and played a key guiding role in the experimental program.2.In the Ho³⁺and Pr³⁺co-doped fluoride fiber laser systems,the Bi₂O₂Se,Al-doped ZnO?AZO?,and Sb materials were used as saturable absorbers,respectively.And the passive Q-switched pulsed laser output was achieved for the first time in the 3?m band:?a?Fabrication of a spatially saturable absorber based on Bi₂O₂Se,and based on which Q-switched laser pulses with a minimum pulse width of 2?s,a repetition rate of up to 62.5 kHz,an average output power of up to 21.5 mW,and a center wavelength of2860.4 nm were obtained.?b?Fabrication of a spatially saturable absorber based on AZO.Based on this,passively Q-switched laser pulses were obtained with the narrowest pulse width is 1.77?s,the maximum repetition rate is 71.43 kHz,the average output power is 26.9 mW,and the center wavelength is 2864.2 nm.?c?Fabricating a spatially saturable absorber based on Sb.Based on this,passively Q-switched laser pulses were obtained with the minimum pulse width is 1.74?s,the maximum repetition rate is 119 kHz,and the maximum average output power is 80 mW.The center wavelength is at 2895.1 nm.3.Based on Er³⁺-doped fluoride fibers,a gain-modulated pulsed laser output with high signal-to-noise ratio and stability at 3?m is realized.Based on the principle of single variable,the 3?m gain-modulated laser pulses were obtained with the pump laser pulse width,repetition frequency and peak power as variables.On this basis,we comprehensively analyzed the relevant experimental results of“multiple production one”,“one production one”and“one production multiple”from their respective perspectives,and obtained a series of conclusions.And we known of gain-modulated fiber lasers comprehensively.In the experiment,we get a stable gain-modulated laser pulse with output average power 241.2 mW,peak power 5.27 W,pulse energy 12.06?J,pulse width2.29?s,repetition frequency 20 kHz,a center wavelength of 2875.5 nm,and signal-to-noise ratio as high as 62.7 dB.