Research On 3.5 μm Er-doped Fiber Laser And Its Pulse Output Characteristics

Since the 21st century,mid-infrared laser at 2～5μm has developed a significant impact in medical research,military and defence force,gas exploration,material processing and other important fields.The continuous and pulse laser at 3.5μm has also been making rapid progress,but it is still unresolved to realize laser output with high power,high efficiency and narrow pulse width.This thesis adopted Er³⁺:ZBLAN fiber to build a dual-wavelength pumped continuous fiber laser at 3.5μm and conducted an experimental research on pulsed lasers at 3.5μm by gain modulation and passive Q-switched.The specific research contents of this thesis are as listed below:1.On the basis of Er³⁺ions′energy level structure of gain fiber and composite wavelength pumped mode,particle level transition processes affecting 3.5μm laser generation were analyzed.Next a theoretical model of 3.5μm continuous fiber laser was built by the rate equation of Er³⁺ions and power transfer equation.Using the model to numerically simulate the laser system,the relationship between 3.5μm laser output and length of Er³⁺:ZBLAN fiber,doping concentration of erbium ions,reflectivity of the cavity output mirror as well as input power of two pump sources were explored.Finally,the simulation showed that when the fiber length,the ion doping concentration and the reflectivity of output mirror are 3.2 m,1.5 mol.%and 60%respectively,3.5μm system can achieve an efficient laser output.This lays a theoretical foundation for the subsequent experiments.2.A Tm-doped 1973 nm all-fiber laser was built independently as the pump source of this experiment and obtained a maximum continuous laser output power of 11.28 W.Then a dual-wavelength pumped continuous fiber laser at 3.5μm was built by the 1973nm pump source and a commercial laser diode at 976 nm.A continuous laser with the center wavelength of 3428.6 nm was obtained,which had a maximum output power of0.984 W and a slope efficiency of 35.4%.Based on the continuous laser,a gain-switched Er³⁺:ZBLAN pulsed fiber laser was constructed by adopting 976 nm pulsed pump.The laser realized a pulse output at 3.5μm with a maximum pulse energy of 48.7μJ and a repetition frequency of 10 k Hz.Using a germanium mirror with Cd As+DBR saturable absorber material instead of the output coupling mirror,a passively Q-switched pulsed fiber laser was built and the exiting problems in this experimental process were analyzed to further optimize the experiment.