# Study of the Effect of Laser Radiation Parameters on the Efficiency of Lithotripsy
## 4 Conclusions  
As a result of the experimental study, we were able to compare the mechanisms of interaction of radiation energy with the material of urinary calculus phantoms using laser radiation of different wavelengths and pulse durations. It is shown that at an average power of about 9 W, the efficiency of removing phantom masses from gypsum by radiation with a wavelength of 1064 nm and a duration of 250 fs is 1.56 g/s. At the same time, a fiber Sp-Tm laser with a wavelength of 1940 nm showed an average result of about 3.19 g/s with a pulse duration of about 1.8 ms, which corresponds to an almost twofold increase in productivity in the femtosecond treatment regime. It is partly due to the discrepancy between the time it takes to remove material and the step of the femtosecond laser scanning head; on the other hand, when analyzing the obtained data on the laser characteristics that affect the processing productivity, we established the fact that the photothermal destruction mechanism is superior to photoionization ablation. At the same time, the magnitude of retropulsion during the treatment of urinary calculi phantoms with a Tm-laser lithotripter averaged 9.6 mm at an average power of 9 W. When using radiation of the same power of femtosecond pulse duration, retropulsion and thermal exposure were not observed. This phenomenon is explained by several factors, among which it is worth highlighting the operating wavelength of the radiation located in the hydroxyl groups' transparency window. This condition makes it possible to avoid significant heating of the liquid around the urinary calculus phantom and prevent the formation of vapor bubbles, which create shock waves due to the cavitation effect after they have collapsed. We also should note the duration of the interaction of radiation with the processed material, during which the radiation energy does not have time to be transferred to neighboring molecules of the material. However, the limiting factor for the femtosecond lasers implementation in LL is the lack of a delivery channel capable of transmitting high peak power radiation. Perhaps, in the future, this problem will be solved by using photonic crystal fibers and hollow-core fibers. In [32; 33], radiation transmission through a hollow-core fiber was demonstrated with a peak power of 0.7 TW in the mid-IR and with a peak power of 100 MW at a wavelength of 1030 nm, respectively. However, the possibility of their use requires practical confirmation. In addition, as far as we know, samples capable of transmitting femtosecond pulses with high-peak-power in a fiber trace with small bending radii (the bending radius of a urethroscope) have not yet been demonstrated. Following the above, we believe that, despite the lower productivity, the absence of retropulsive and thermal effects on the environment should favorably affect both the quality of the operations themselves and the postoperative recovery process of the patient.  
Conceptualizatio, M.Y.P., N.V.A., O.I.A., V.E.K. and A.G.G.; Data curation, A.V.P.; Formal analysis, I.O.O., A.E.S. and S.G.S.; Funding acquisition, O.I.A., V.E.K. and A.G.G.; Investigation, I.O.O., A.V.K., I.A.K. and V.M.B.; Methodology, A.V.K., A.E.S. and S.G.S.; Project administration, I.A.K.; Resources, M.Y.P. and N.V.A.; Supervision, V.E.K. and A.G.G.; Validation, A.V.S. and A.V.P.; Visualization, V.M.B.; Writing--original draft, I.O.O., M.Y.P. and N.V.A.; Writing--review and editing, A.V.K., I.A.K., A.E.S., S.G.S., A.V.S., O.I.A., V.E.K. and A.G.G. All authors have read and agreed to the published version of the manuscript.  
This research was funded by Bauman Moscow State Technical University.  
Not applicable.  
Measurement data are available per request by corresponding author email.  
The authors declare no conflict of interest. The funders had no role in the design of the study, the collection, analysis, or interpretation of data, the writing of the manuscript, or the decision to publish the results.