Ho:YAG and Thulium Fiber Laser Radiation Transmission Through Vapor Channels in Laser Lithotripsy

The efficiency of energy deposition during laser lithotripsy is strongly influenced by the interaction between laser radiation and the water layer between fiber tip and stone. This study investigates the transmission of holmium:YAG (Ho:YAG) and thulium fiber laser (TFL) radiation through vapor channels under varying fiber-to-target distances (0.5-3 mm). Both lasers were set to deliver pulses of 1 J. The fiber was positioned in a water-filled cuvette on top of an integrating sphere to measure transmittance through different water layer thicknesses. A 580 μs, high-power (up to 7 kW) Ho:YAG laser pulse creates a vapor channel that enables continuous transmission of the laser energy to the target surface for standoff distances > 0.5 mm. With the TFL's longer (2 ms), lower peak power (500 W) pulses, repeated cycles of vaporization and bubble collapse occur, resulting in a reduced energy transmission efficiency compared to the Ho:YAG laser pulses.