Reasearch On Mid-infrared Pulse Laser And Its Pump Technology Based On Fluoride Fiber

The advantages of fiber lasers are high-quality beam quality,good heat dissipation,easy miniaturization and integration.They have very important application prospects in various fields such as laser processing,medical treatment and military.In particular,the 3-5?m mid-infrared fiber lasers are in the atmospheric transmission window have been received extensive attention from infrared countermeasures,gas detection and biomedicine.However,the traditional optical fiber is made by quartz material.This material has a large phonon energy and the larger transmission loss when the wavelength exceeds 2.2?m.The fluoride material has lower phonon energy and is a commonly used as fiber material for mid-infrared fiber lasers.In recent years,with the continuous improvement of fluoride fiber drawing technology and device production level,mid-infrared fiber laser has been developed rapidly.However,there are still many problems to be solved and explored urgently.This paper adopts modulation methods such as Q-switching and mode-locking to carry out related theoretical and experimental research on the mid-infrared fluoride fiber pulse laser and its pumping technology.First of all,the application prospects of mid-infrared fiber lasers have been introduced and the technical solutions to achieve mid-infrared lasers have been summerized.The advantages of mid-infrared fiber lasers are highlighted.The recent research progress of 3?m band Er³⁺doped fluoride fiber lasers,3.5?m band Er³⁺doped fluoride fiber lasers and 3.9?m band Ho³⁺doped fluoride fiber lasers have been summarized.And the future development directions are condensed.Secondly,the relationship between the pump power,fiber length and laser threshold of a 976nm pumped 2.8?m fluoride fiber laser has been theoretically analyzed according to the laser rate equation.On this basis.the theoretical research on the output characteristics of cascade pump 3.5?m fluoride fiber laser has been carried out.According to the heat transfer equation,the temperature distribution model in the fluoride fiber has been established.And the influence of absorption coefficient,ambient temperature and thermal conductivity on the temperature distribution in the fiber has been analyzed.According to its deliquescence equation,the effects of activation energy,environmental humidity,ambient temperature and pump light power on its deliquescence rate are analyzed.Lay a theoretical foundation for the design of fluoride fiber laser.Then,in response to the demand for a 2?m pump light source in cascade pump Er:Zr F₄fiber lasers,relevant research has been carried out.First,the research on Ga Sb-based semiconductor lasers has been carried out.When the feedback length of external cavity is 45cm,the self-pulse output is realized and the frequency of pulse repetition is 153MHz.The off-axis feedback method has been used to improve the beam quality from 25.5 to 12.7.And the brightness is also improved.However,it can't meet the needs of core-pumped Er:Zr F₄fiber.For this reason,we have carried out related research on Tm-doped fiber laser(TDFL).Based on the all-fiber structure of TDFL,the maximum power is 6W and the center wavelength is 1980nm.And the relevant experimental research of the mode-locked TDFL has been also carried out.By optimizing the cavity structure,the mode-locked pulse with a repetition frequency of 20MHz,pulse width of 1.7ps and an average power of 509m W has been realized.Then,carry out related experimental research on 2.8?m Er:Zr F₄fiber laser pumped by 976nm diode laser.On the basis of achieving continuous outpu power of2.3W,40MHz self-mode-locked pulse output are achieved by optimizing the pump power.The frequency of pulse repetition can be adjusted by changing the feedback distance of the external cavity.At the same time,we also carried out an experimental study of a 2.8?m Q-switching pulsed laser based on SESAM.Finally,a pulsed laser with a pulse width of 2?s,a center wavelength of 2784nm and a pulse repetition frequency of 68k Hz has been achieved.Furthermore,On the basis of the previous work,it has been carried out experimental research on cascade pump of Er-doped fluoride fiber to achieve 3.6?m laser output.A single-mode fiber coupling system was constructed based on ZEMAX software.It was analyzed that the influence of the position deviation and angle deviation of the coupling fiber on the coupling efficiency of the system.A 1980nm pump absorption test system has been built.The coupling efficiency of 80%was achieved by optimizing the coupling system.On this basis,a cascade pump Er-doped fluoride fiber laser system has been built and it has been successfully realized lasing.The center wavelength of the laser output was 3647nm.The highest output power is 110m W by optimizing the power of the two pump lights.Finally,the research has been done to solve the problem of high threshold and difficulty to achieve 3.9?m Ho:In F₃fiber laser pumped by 888nm diode.A 888nm pumped Ho:In F₃optical fiber fluorescence test system has been built.When the pump light reached 4.4W,a weak 3.9?m fluorescence was detected.At the same time,fluorescence at 660nm and 493nm was also detected,indicating that there is an excited state absorption process in the system.Based on the fluorescence test results and theoretical calculations,the reasons for the high 3.9?m laser threshold have been analyzed.Multi-wavelength feedback mirrors and dual-wavelength pumping have been proposed to achieve the effect of lowering the laser threshold of 3.9?m.