Compared with traditional solid-state laser,fiber laser has been developing rapidly in recent years in domestic and international research due to its stable function,compact structure,high conversion efficiency,and strong anti-interference performance.Thulium-doped fiber laser(TDFL)operates in the safe band of human eyes,and has broad prospects in many fields such as biomedicine,material processing,remote sensing and detection.In this thesis,the main oscillation power amplification(MOPA)structure is used to design a thulium doped all-fiber laser system for the application of laser in the urinary system,and the high power laser output in the 2μm band is realized.The safety and advancement of 2μm thulium-doped fiber laser in biomedicine was verified by the ablation of urinary calculi with 2μm laser source.The main research contents are as follows:Firstly,the classification,characteristics and application of fiber laser in medical field are discussed.The operating principle of thulium-doped laser is described in detail in terms of the spectral properties,energy level structure and pumping mode of thulium ions.The working principle of the main oscillating power amplification structure and the factors limiting its further power amplification are presented.The research status of thulium laser lithotripsy at home and abroad is introduced,and the significance of research on 2μm thulium doped laser lithotripsy is expounded from the perspective of urinary lithotripsy.This article introduces the main methods of urinary stone treatment,discusses the characteristics of traditional holmium solid laser lithotripsy and thulium fiber laser lithotripsy,and compares their advantages and disadvantages.Secondly,there are few reports on thulium-doped fiber laser with high power MOPA structure,while the research on high-power MOPA ytterbium-doped fiber laser(YDFL)has been very mature.Therefore,the principle experiment of all-fiber MOPA structured YDFL is carried out to explore the selection of basic structural parameters for the research of 2μm thulium-doped fiber laser.A ytterbium-doped fiber laser with MOPA structure is designed.In continuous wave(CW)mode,the laser with a central wavelength of 1069.96 nm is output after the seed light passes through ytterbium-doped fiber amplifier,and the maximum average output power is up to 945.9W.The slope efficiency of the MOPA laser is up to74.12%,which shows great robustness.Thirdly,a 2μm low-noise narrow-linewidth MOPA structured TDFL was designed for urinary stone ablation,which can be adjusted in both continuous wave and quasi-continuous wave(QCW)modes.2μm TDFL has a maximum average output power of 66.9W and a corresponding slope efficiency of 47.58%.In QCW mode,the laser output can be achieved with a repetition frequency of 50-2000 Hz,adjustable pulse width of0.5-20 ms,and peak power of up to 80.3W,which meets the parameter requirements of laser lithotripsy surgery for laser light source.Finally,TDFL with low noise and narrow linewidth at 1940 nm is used as a laser source to simulate lithotrification of urinary calculi samples in vitro.The influence of laser parameters such as repetition rate and single pulse energy on ablation rate and ablation threshold are studied,and the influence of laser parameters on stone escape displacement is explored.The experimental results show that the stone ablation threshold of TDFL lithotripsy is 4 times lower than that of traditional holmium solid laser lithotripsy.The experimental results show that the stone ablation rate increases with the increase of pulse repetition rate,but the growth rate is not linear.The optimal range of pulse repetition rate is50-100 Hz.Under the condition of constant single pulse energy,the average laser output power is the main factor affecting the calculus ablation volume.TDFL output laser will generate more heat at long pulse width,resulting in greater temperature rise near the stone.The best combination of laser parameters to reduce the reverse escape displacement of stones is to use the output fiber with lower pulse energy,larger pulse width,lower pulse repetition rate and smaller core diameter. |