Study On Mid-infrared 3 ?M Band Er-doped ZBLAN Fiber Laser

Mid-infrared laser(2?20 ?m)locates in the vibration and rotation absorption band of many moleculars,the so-called molecular fingerprint region,which makes mid-infrared laser has potential applications in disease diagnosis,trace gas detection,and molecular spectroscopy.Besides,there are three transparent windows in space atmosphere and they locate at 2?2.7 ?m,3?5 ?m,and 8?13 ?m,respectively.Thus,the mid-infrared lasers can be applied to remote sensing,space communication,and national defense.The development of visible and near-infrared lasers tends to be mature,however mid-infrared laser,especially the above 3-?m laser,lags seriously.This thesis focuses on the 3 ?m band Er:ZBLAN fiber laser and carried out the research of complex transitions and laser radiation in numerical simulation.We developed the black phosphorus(BP)saturable absorber as Q-switched and mode-locked devices,and demonstrated the high-power pulsed laser at 3 ?m.Our research works promoted the development of 3 ?m mid-infrared laser and established the foundation for the application of 3 ?m mid-infrared laser technology.The main work is as follows:1.Based on the rate equations of population densities and the power evolution equations in the fiber,we numerically simulated the transitions and the stimulated emission of Er-doped ZBLAN fiber at the wavelength of 2.8 ?m.In the calculation model,we added the new energy transfer process to rate equations and the stimulated emission of pump to power evolution equations.The calculation from the modified model is more consistent with the experimental results.Based on the modified model,we studied the excited state absorption(4I11/2?4F7/2),related to the upper laser level pump,and the effect of core temperature on the average output power.The results agreed with the experimental results and also gave a good explanation of the saturation effect of output power at a high pump power.In addition,we established the model related to the stimulated emission of Er-doped ZB LAN fiber at the wavelength of 3.5 ?m,demonstrating the feasibility of the dual-wavelength pumping scheme to generate 3.5?m mid-infrared laser.2.Due to the lack of mature and reliable saturable absorber at 3 ?m,we developed a new type of BP saturable absorber.It has a band gap of 0.3?2 eV,which can be flexibly adjusted by changing the number of layers.The variable bandgap makes BP apply to mid-infrared lasers with different wavelengths.With the mechanical exfoliation and liquid-phase exfoliation methods,we fabricated the mid-infrared broadband BP saturable absorber mirrors.3.We used the as-prepared BP saturable absorber mirror as optical modulator,developing the high-power 2.8 ?m Q-switched Er:ZBLAN fiber laser and it is the first time to confirm that the BP can be used as a 3 ?m saturable absorber.The Q-switched fiber laser output the maximum average output power of 485 mW,pulse energy of 7.7 ?J,and pulse duration of 1.2 ?s,which can be used as a pump source in infrared Raman fiber laser to further extend laser wavelength.4.By employing BP saturable absorber mirror as mode-locker,we achieved high-average-power mode-locked pulses from 3 ?m Er:ZBLAN fiber laser.We compared the BP saturable absorber mirror and commercial SESAM in the same laser system with the respect of average power,pulse width and stability etc.The results showed that BP saturable absorber mirror,developed by us,can be comparable to commercial SESAM.Because the commercial SESAM could only work up to 3 ?m wavelength,BP saturable absorber mirror can cover longer in infrared wavelengths,creating a condition for generating above 3-?m ultrashort pulse lasers.In short,our thesis not only studied the fundermental transitions and laser emission process in the Er:ZBLAN fiber laser,but also systemtecially researched the design and optimization of laser system,development of BP saturable absorber,laser performance of high-average-power Q-switched and mode-locked lasers.Our research works promote the development and create the condition for application of 3-?m mid-infrared fiber laser.