## 2 Materials and Methods  
Experimental studies were performed in a transparent cuvette filled with 0.9% saline solution (NaCl) using the superpulse thulium fiber laser. We used end-firing laser fibers with a core diameter of 600 \(\upmu\)m. The lithotripsy experiments were carried out on cubic stone phantoms (BegoStone) with an edge size of 5 mm. The stone phantoms were exposed to laser radiation with the following parameters: average power \(\mathrm{P_{av}=10\ W}\), pulse duration \(\tau=0.4\) ms, pulse energy \(\mathrm{E_{P}=0.2\ J}\), and peak power \(\mathrm{P_{P}=500\ W}\), which provided the so-called dusting mode of stone disintegration. In total, three series of experiments were carried out, in which 7 BegoStones were used. We installed a wideband hydrophone 8103 (Bruelk&Sjaer, Narum, Denmark) with a 0.1 Hz-180 kHz band (sensitivity \(-211\) dB re 1 V/\(\upmu\)Pa) in the cuvette \(\approx\)3 cm from the fiber end perpendicularly to the fiber optical axis. For the registration of high-frequency acoustic signals, a needle hydrophone (Precision Acoustics, Dorchester, UK) with a diameter of 1 mm and with a 10 kHz-50 MHz bandwidth (sensitivity \(-241\) dB re 1 V/\(\upmu\)Pa) equipped with a pre-amplifier was installed \(\approx\)1 cm from the end of the fiber. Acoustic signals obtained with hydrophones were recorded by a four-channel digital storage oscilloscope GDS 72,304 (GW Instek, Taipei, Taiwan) with a 300 MHz bandwidth. An optical registration of laser-induced processes near the fiber end in water was performed with a high-speed camera Fastcam SA-3 (Photron, Tokyo, Japan) (4000 fps, frontal light through the cuvette, shadowgraph technique). The fragment of the installation with a transparent cuvette and the layout of the configuration of its separate elements during the stone phantom laser exposure are presented in Figure 2. The stone phantom was fixed on a special stationary holder. The phantom was exposed to the laser in a contact mode when the fiber end firmly meets its surface. Figure 1: Dependence of the absorption coefficient of water (22 \({}^{\circ}\)C) on the wavelength of radiation in the area of the local peak \(\approx\)2 \(\upmu\)m [14]. The evaluation of the clinical efficiency of laser radiation with \(\lambda\) = 1.94 um and 500 W maximum peak power was based on the results of its clinical application [15,18]. In the Institute for Urology and Reproductive Health of the Sechenov University, retrograde flexible nephrolithotripsy, mini percutaneous nephrolithotripsy, endoscopic ureterolithotripsy, and cystolithotripsy are performed using the follow equipment: fibers with core diameters of 200, 400, and 600 um, respectively. Retrograde flexible nephrolithotripsy is performed using a disposable digital flexible ureterroscope with an external diameter of the tube 9.5 Fr, an operating channel of 3.6 Fr, and an angle of deflection of 270\({}^{\circ}\) in both directions (upwards and downwards). During mini percutaneous nephrolithotripsy, a rigid nephroscope 16.5/17.5 Ch with an offset eyepiece 120 is used. Endoscopic ureteral lithotripsy is performed with a rigid urethroscope [PERSON] 8/9.8 Ch with an offset eyepiece 120 and [PERSON] 7/12 Ch. Contact cystolithotripsy is performed with an operating element KUNTZ with a resectoscope tube 26 Ch. Retrograde intrarenal surgery is performed using two modes of laser radiation, wherein the pulse energy ranged from 0.15 to 0.8 J and average power ranged from 15 to 30 W. The dusting mode with a high repetition rate (30-200 Hz) is optimal to provide good stone disintegration with the formation of very fine particles and create conditions for their free passage.