Holmium laser in solid state has become one of the commonly used lasers in kidney stone surgery because of its high productivity, safety and wide application. However, there are some problems with lithotripsy of holmium laser, like pulverizing stones insufficiently or exerting thermal effects. Tm-doped fiber laser promises to solve these problems with laser lithotripsy because it has its specific emission wavelength, high conversion efficiency, good beam quality and stable structure. Because of its wavelength’s covering water absorption peak, high peak power, and low pulse energy, 2 μm ultrafast laser can increase the efficiency of breaking stones, and decrease the thermal damage to peripheral soft tissue. Therefore, 2 μm picosecond thulium doped fiber laser was constructed and in vitro studies were conducted to explore the effect and mechanism of 2 μm laser lithotripsy.Linear-cavity SESAM mode-locked fiber laser was used as seed source, and the amplification method of MOPA structure was applied. Thus the high peak power picosecond laser pulse was achieved, with the wavelength of 1962 nm, the pulse width of ~50 ps and the peak power of over 20 kW, as shown in Fig.1-Fig.3. Set up a laser lithotripsy optical path device, as shown in Fig.4. Laser output was collimated through a lens with a focal length of 100 mm, and then residual pump light was filtered out using a dichroic mirror. Three mirrors were used to control the laser transmission trajectory, and finally operated a lens with a focal length of 50 mm to focus the laser. By adjusting the distance between the lens and the sample, controlled the laser to focus on the sample with spot diameters of 200 μm, 300 mm, and 400 μm, respectively. Placed the stone in a culture dish, added water to a depth of less than 1 mm, and performed laser lithotripsy for 30-120 s, breaking it into small pieces as much as possible. Due to the ability of the human body to expel stones smaller than 2 mm on its own, a 2 mm sieve was used for continuous filtration of stone fragments. Then placed the stone in a drying oven at 80 ℃ for 10 minutes to dry the surface moisture of the stone. Measured the mass of stones before and after the experiment using an electronic balance, with three measurements per experiment. Maintained a distance of 2 mm between the probe of the digital temperature tester and the stone, recorded the temperature changes before and after laser lithotripsy to study the influence of liquid thermal effects during the lithotripsy process.With the increase of laser power and the decrease of spot size, the mass reduction of stones significantly increases, as shown in Fig.5(a). With the combination of minimum laser power and maximum spot size (5 W, 400 μm), the reduction in stone mass was the smallest ((5.8 ± 1.1) mg); When the highest laser power was combined with the minimum spot size (12 W, 200 μm), the reduction in stone mass reached its maximum ((75.2 ± 9.1) mg). In addition, Figure 5(b) further indicated that during the 120 s experimental period, the fragmentation efficiency of picosecond thulium doped laser remains relatively stable, and there was no significant fluctuation in the mass of melted stones every 30 seconds. Confirmed the close relationship between the efficiency of picosecond thulium laser lithotripsy and power density. Under a fixed spot size, increasing the laser power could effectively increase the energy density per unit area, thereby promoting faster ablation of stones. Meanwhile, reducing the size of the light spot could further improve energy concentration and enhance stone crushing efficiency at the same power.Linear-cavity SESAM mode-locked fiber laser was used as seed source, and the amplification method of MOPA structure was applied. The high peak power picosecond laser pulse was achieved, with the wavelength of 1962 nm, the pulse width of ~50 ps and the peak power of over 20 kW. Vitro lithotripsy studies showed that increasing laser power can effectively increase the energy density per unit area under a fixed spot size, thereby promoting faster ablation rate of stones. At the same time, reducing the size of the light spot could further improve energy concentration and enhance stone crushing efficiency at the same power. The efficient fragmentation efficiency during the interaction between picosecond thulium laser and stones wad related to the micro explosion of pore fluid caused by the short pulse and high peak power of picosecond laser. However, the specific mechanism of action and parameter optimization still required extensive research in the future. In summary, these preliminary research results indicate great potential for future applications in the field of short pulse picosecond laser lithotripsy.