Research On Er-doped Fluoride Fiber For Q-switched And Mode-locked Pulses In 3 ?m Mid-infrared Band

Mid-infrared(MIR)lasers have important applications in military confrontation,biomedicine,gas sensing,and spectroscopy.In recent years,with the maturation of fluoride fiber drawing technology,fiber lasers in the mid-infrared wavelength(2-5?m)have also developed vigorously.Two important wavelengths of 2.8?m and 3.5?m have been intensively studied.The power of mid-infrared continuous-wave fiber lasers is constantly increasing,while the research of mid-infrared pulsed lasers still has room for development.But for now,the means of yielding mid-infrared pulsed lasers are still limited.Based on the application requirements of the mid-infrared pulsed fiber laser and the problems in technical research,combined with the traditional saturable absorber pulse generation method and focusing on the new mid-infrared synchronously pump mode-locked method,the research of the mid-infrared pulsed fiber laser is carried out.The research content is as follows:1.The main uses of mid-infrared lasers in military,livelihood medical and scientific research fields are summarized,and the development overview of 2.8?m and 3.5?m wavelength mid-infrared pulsed fiber lasers is emphasized.Introduce the methods currently available for generating mid-infrared pulses,which mainly involve the Q-switching and mode-locking mechanisms of saturable absorbers(SAs).It is proposed to realize the mid-infrared pulsed fiber laser using synchronously pump mode-locking technology.2.The study of SAs materials suitable for the mid-infrared band mainly involves relatively novel metal antimony(Sb)materials and traditional single-wall carbon nanotubes(SWCNTs)materials.Using Sb material as the saturable absorber,Sb-SAM was prepared based on the magnetron sputtering deposition method(MSD),and a 2.8?m mid-infrared Q-switched fiber laser based on erbium-doped ZBLAN was realized.A 2.8?m Q-switched pulsed laser was obtained with a repetition rate of 57.0 k Hz,a narrowest pulse width of1.7?s,and a highest single pulse energy of 1.03?J.The SWCNT saturable absorber mirror(SAM)was prepared by drip coating,and then a 3.5?m mid-infrared mode-locked fiber laser was realized.3469.7 nm mode-locked pulses trains were obtained with the output power was 25.0 m W(pulse energy of 0.98 n J),a repetition rate of 25.2 MHz,and the pulse width was about 1 ps(Fourier Variation limit pulse width).3.The feasibility of synchronously pumping mode-locked pulses in a linear cavity mid-infrared laser is verified,which was synchronously pumped by a 1.5?m pulse laser and based on the common all-fiber structure.Utilising a 1.5?m electrically modulated semiconductor laser as a seed source,through three-stage amplification,a 1.5?m pulse laser with a pulse width of 3 ns and a maximum output power of 1.5 W is realized.Using this as a pump source,a 2?m linear cavity synchronously pumped mode-locked pulse was achieved with a maximum output power of 150 m W,a repetition frequency of 7.454 MHz,a pulse width of 3 ns,and a center wavelength of 1955.8 nm.This is the first time to realize a synchronously pumped mode-locked fiber laser based on a 2?m line cavity.4.Based on the realization of 2?m synchronously pumped mode-locked fiber laser,a3.5?m fiber laser based on synchronously pumped mode-locked fiber laser was proposed.Using a 1973 nm electrically modulated semiconductor laser as the seed source,through a Master Oscillator Power-Amplifier,a 1970.8 nm pulse laser with a pulse width of 3.3 ns and a maximum output power of 8 W was obtained,which was then pumped with Er³⁺:ZBLAN fiber.Finally,a mid-infrared 3462.2 nm mode-locked pulsed laser was achieved with a maximum output power of 120 m W,a repetition frequency of 22.382 MHz,and a pulse width of 10 ns.This is the first 3.5?m synchronously pumped mode-locked fiber laser,and the experiment proves the applicability and universality of the synchronous pumped mode-locking technology at 2?m and even 3.5?m wavelengths.