2μm High Power Fiber Laser For Urinary Lithotripsy

Thulium-doped fiber laser（TDFL）has many advantages such as compact structure,high flexibility,high heat dissipation,good beam quality,and easy integration,and the emission wavelength can perfectly match the absorption peak of water at 1940 nm,which is very suitable for application in the urological system for laser lithotripsy.The most widely used laser with the best clinical results is the holmium laser with low tissue damage and high safety,but the solid holmium lasers used in conventional lithotripters are large,unreliable,difficult to tune,and expensive.In this thesis,a high-power TDFL for urinary lithotripsy was designed to address the shortcomings of the solid holmium laser lithotripter,and it was applied in an extracorporeal lithotripsy simulation experiment.The details of the study are as follows:1.A numerical model of TDFL is established,and a simulation link is built using Optisystem platform to analyze the effects of TDF length,OC-FBG reflectivity and Tm³⁺doping concentration on the output performance of the laser in the TDFL system.The simulation shows that there are optimal values of TDF length,OC-FBG reflectivity and Tm³⁺doping concentration to maximize the output power and optical-optical conversion efficiency of the TDFL.The simulation experiment provides guidance for the design of 2μm fiber lasers.2.The output characteristics of the 793 nm pump source（LD）and seed source lasers were investigated by designing a 2μm linear cavity seed source laser,respectively.The pump output power is in an overall rising trend with increasing electrical power,with a nonlinear increase and a threshold current.Although the output wavelength of the LD drifts with the increase of the LD temperature,both LDs in this experiment meet the experimental requirements at the center wavelength of the spectrum at room temperature.The center wavelength of the seed source laser is 1940 nm,the 3 d B spectral linewidth is 0.09 nm,and the maximum output laser power of 18.56 W is obtained at full power output of the LD,and the corresponding optical-optical conversion efficiency and slope efficiency are 49%and54.84%,respectively.3.A 2μm fiber amplifier was designed and fused to the previous seed source laser to obtain a TDFL with a master oscillation power amplification（MOPA）structure,which can achieve both continuous and quasi-continuous mode outputs.The maximum output power of the MOPA laser in continuous mode is 66.9 W,the slope efficiency is 48.48%,the laser center wavelength is 1940 nm,and the spectral half-height full width is 0.10 nm.The maximum peak power in quasi-continuous mode is 80.3 W,and the pulse energy is 1.33 J.Then,this 2μm MOPA structured fiber laser was applied to the in vitro lithotripsy experiment,and it was verified that the thulium laser with the wavelength of 1940 nm designed in this experiment could break up the stones with fragments much smaller than the2 mm limit for natural discharge through the urethra.