Research On Large Mode Field Thulium-doped All-fiber Laser

The output spectrum range of Tm-doped fiber laser covers 1.6?m~2.1?m,which has a varied applications.2 ?m pulse laser is the efficient pump source for mid infrared 3~5?m and far infrared 8~12?m laser optical parametric oscillator(OPO).The mid and far infrared laser has an important applied value in the field of optoelectronic countermeasure,laser guidance and so on.With the study of mid and far infrared applications deepened,deep space exploration,remote infrared guidance,laser radar,wide range and long distance laser application become a focus of scientific researchers.It requires high power pump source to meet the needs of the new situation.In account of this,this dissertation is devoted to the design and construction of high power all-fiber laser.It is expected to make certain contributions to the research and application in the related fields.Thulium ion quasi three level rate equation model is established based on silicon fiber.The forward laser and the backward laser output power and the length of the fiber is simulated and discussed by numerical simulation at forward pumping mode.The relationship between the laser output power and the active fiber length with different pump powers,different fiber doping concentrations and different laser gain-loss differences is discussed.An all-fiber oscillator is designed and fabricated with 25/250?m Tm-doped fiber.The laser output characteristics of the dual fiber Bragg gratings(FBGs)forward and backward pumping modes and the single FBG forward pumping mode are compared and analyzed.High power all-fiber laser oscillator is designed and fabricated by 25/400?m large mode area(LMA)Tm-doped fiber.In order to increase the laser output power,the theory and experiment on fiber laser amplifier are studied.A theoretical model for Tm-doped fiber amplification is established.The relationship between the laser output power and the active fiber is numerically simulated under different seeds injection and different pump powers.Laser amplifiers based on MOPA(Master Oscillator Power-Amplifier)structure at 1.91?m and 1.94?m are designed and constructed.The gain saturation of fiber laser amplifier is analyzed.Finally,152 W of output power is obtained at 1908.3nm,and 141 W of output power is obtained at 1939.6nm.Continue wave(CW)laser and pulse Q-switched(PQS)laser operating at 2.05?m produced by Ho:Gd VO4 solid-state laser is amplified by Tm3+-doped fiber for power scaling.Laser seeds are coupled to Tm3+-doped fiber through a self-made fiber end cap by means of spatially coupling.The laser slope efficiency is 17.7% in CW mode and 10% in PQS mode.The higher pulse repetition frequency is,the higher slope efficiency of the fiber amplifier is.The maximum 17 W laser output is obtained in fiber laser amplifier with a slope efficiency of 10.2%,a pulse width of 24 ns,a single pulse energy of 3.4m J,and a peak laser power of 142 k W at 5k Hz.It is found that the output laser pulse broadening is related to the fiber length of the fiber amplifier,and the pulse broadening rate is about 1.25ns/m.Finally,the experiment of 1.94?m fiber laser pumped Ho:YLF crystal is designed and constructed.The passively Q-switched experiment is performed by inserting Cr2+:Zn S saturable absorber.The relationship of the average power,pulse repetition frequency,pulse width,pulse energy and peak power with respect to the pump power is measured.Under 18.7W injection pump power,the maximum 6.03 W of pulse laser output is obtained,and the laser slope efficiency is 45.9%.The laser output wavelength is 2050.1nm,and the beam quality factor of M2 is 1.05.