# Study of the Effect of Laser Radiation Parameters on the Efficiency of Lithotripsy
## 1 Introduction  
Today, the prevalence of urolithiasis varies from 2 to 15% in different regions of the world, with a general upward trend. Studies in the United States have shown that urolithiasis prevalence increased from 3.6% in 1976-1980 to 10.1% in 2015-2016 [1]. The urolithiasis prevalence in 2023 in Western Europe was about 5-9%, in Canada 12%, and in the United States 7-15%. Kidney stones affect approximately 1 in 11 people in the United States [2]. The prevalence of urolithiasis in the eastern hemisphere is about 1-5% [3; 4; 5]. However, it is worth noting that approximately 60% of all kidney surgeries are performed for urolithiasis. However, surgical treatment is not isotropic and is fraught with complications of varying severity, and almost one-third of operated patients experience calculi recurrence. The percentage of severe complications increases proportionally with the frequency of surgical interventions in patients with nephrolithiasis. Due to this fact, current trends in operative urolithiasis treatment are aimed at reducing the \"invasiveness\" of the intervention. Endouurgical surgical interventions (contact ureteral lithotripsy, retrograde intrarenal surgery, and percutaneous interventions) and extracorporeal remote shockwave lithotripsyare considered to be the main methods of urolithiasis surgical treatment [6; 7; 8; 9; 10]. Methods of urinary stone crushing are constantly studied and improved by the global scientific community. It is worth noting that, to date, the most active research in the urology field has been aimed at developing new methods of delivery of concentrated energy flows for the destruction and disintegration of urinary stones. Thus, in recent years, the laser lithotripsy (LL) method has been actively introduced into clinical practice. From the 1990s until the 2000s, neodymium solid-state lasers with a wavelength of 1064 nm, pulse energy from 1 to 10 J, and pulse duration from 1 to 2 us were used [11; 12]. The residual fraction size of renal concrements after treatment with such lasers ranged from 2 to 4 mm [13]. At the same time, the thermal influence zone was of the order of 1 to 2 mm [14]. LL with a neodymium laser is mostly shockwave in nature, which entails the formation of large residual fractions and a significant thermal effect. In this regard, we can talk about the extremely low efficiency of this approach and the long rehabilitation period. In the second stage of laser lithotripsy from 2000 to the present, using solid-state holmium laser lithotripers with a wavelength of 2120 nm, a pulse energy of the order of 1 J, a pulse duration of 300 us, and an energy density of 200 to 600 J/cm\({}^{2}\)[15; 16]. The thermal influence zone during such treatment is about 300 um [14]. The residual fraction size ranges from 1 to 2 mm [16; 17]. LL by holmium laser has a photothermal [11] character; therefore, it differs in the residual fraction average size and universality of influence on renal concrements of various chemical compositions, which causes the feasibility of its use concerning neodymium lasers. The third stage of laser lithotripsy development is the search for and mastery of new promising laser emitters and treatment methods. Among the promising emitters, we should highlight the erbium laser (Er: YAG) and thulium fiber laser (Tm: fiber) [17; 18; 19; 20; 21]. Er: YAG uses laser radiation with a wavelength of 2940 nm, a pulse energy in the order of 100 mJ, a pulse duration of 300 us, and an energy density of processing 50-700 J/cm\({}^{2}\). The thermal influence zone during such treatment in various works is from 5 to 50 um [14]. LL with erbium laser is photothermal and is more effective than neodymium laser (Nd: YAG) and holmium laser (Ho: YAG), but has large unresolved problems of radiation delivery due to the long wavelength [17]. Tm: YAG uses laser radiation with a wavelength of 1940 nm, pulse energy up to 8 J, and a pulse duration of 50 ms. The residual fraction size is 0.25 mm [22].