Erbium-doped Fluoride Pulsed Fiber Laser And Its Time-Frequency Characteristics

Wavelength between 2-5μm-band mid-infrared laser covers the absorption windows of most gas,liquid and solid molecules and the characteristic absorption spectra of various functional groups.It has important applications in many fields,such as biomedicine,atmospheric environment monitoring,resource exploration,radar detection and so on.Among them,mid-infrared fiber laser has become a research hotspot of mid-infrared laser technology because of its high beam quality,high light-to-light conversion efficiency and compact system.With the continuous improvement of optical fiber manufacturing technology,the continuous maturity of pump light source technology and the deepening of the research on laser generation mechanism,the mid-infrared fiber laser with high power,high energy and narrow pulse width has developed rapidly.However,compared with the visible and near-infrared bands,the mid-infrared band materials and optoelectronic components with low loss and excellent optoelectonic characteristics are relatively scarce,and the improvement of the performance of the mid-infrared laser is restricted.At present,researchers have achieved high-power continuous-wave and pulsed mid-infrared fiber laser output.However,with the application demand of mid-infrared fiber laser with high power,narrow pulse width and high stability,the performance parameters of mid-infrared pulse fiber laser light source need to be improved.This thesis mainly focuses on the application requirements of mid-infrared fiber laser with high power,high efficiency and high stability.The actively Q-switched erbium-doped fluoride fiber laser with acousto-optic switcher and passively Q-switched erbium-doped fluoride fiber laser with PtTe₂ nanosheets saturable absorber and their output characteristics have been studied.The contents are summarized as follows:（1）Based on acousto-optic Q-switcher and volume Bragg grating（VBG）,an actively Q-switched erbium-doped fluoride fiber laser with high energy,narrow pulse width and wide tuning has been obtained.An erbium-doped fluoride fiber laser based on acoustooptic Q-switcher has been designed and built.The evolution of pulse laser output characteristics under different pump power incidence conditions has been studied by changing the modulation frequency.The maximum average power and the shortest pulse width are 64 m W and 515 ns,respectively,and the slope efficiency is18.6%.By introducing VBG as the wavelength tuning element,the widely wavelength tunable erbium-doped fluoride fiber laser output with a maximum of 124 nm（2716 nm～2840 nm）has been realized.When the pump power is 3.5 W,the highest output power of 0.245 W is obtained,which verifies the role of VBG in wavelength tuning and narrowing spectrum of mid-infrared fiber laser.（2）Based on PtTe₂ nanosheets saturable absorber,the stable passively Q-switched erbium-doped fluoride fiber laser output with repetition rate of 31.01 k Hz～173.38k Hz and pulse width of 600 ns has been obtained.The layered PtTe₂ saturable absorber was successfully prepared by liquid phase stripping method,and the nonlinear optical response characteristics of PtTe₂ nanosheets were measured by Z-scan platform.The modulation depth and saturation intensity were 27.8%and 46.5 GW/cm²,respectively.Based on PtTe₂ saturable nanosheets absorber,stable Q-switched pulse output with repetition rate of 31.01 k Hz～173.38 k Hz was obtained.When the maximum pump power is 5.6 W,the average output power and pulse width are 590 m W and 600 ns respectively,and the signal-to-noise ratio of Q-switched pulse is 30 d B.The experimental results show that PtTe₂ has excellent nonlinear optical properties in the mid-infrared band.