Abstract

We have previously demonstrated that the flashlamp-pumped Ho:YAG laser is an attractive alternative to the FDA-approved pulsed dye laser for gallstone lithotripsy. We report here that the mechanism of fragmentation for the Ho:YAG laser differs substantially from that for the dye laser. Fragmentation occurs as a three-step process: The laser first melts an area on the surface of the stone. The molten material is then ejected into the surrounding aqueous ambient, where it rapidly cools and recrystallizes. Finally, the newly formed crystallites are swept away by macroscopic motion of the surrounding liquid, the result of rapid expansion and contraction of a vapor bubble produced by the laser pulse. We show that absorption of the laser light by both the stone and the water is required for efficient fragmentation. This is in contrast to lithotripsy with the dye laser, where fragmentation is believed to be initiated by a shock wave.

© 1992 Optical Society of America