This paper describes in simple terms the physics of
laser-
calculus interactions and introduces a method with which physicians can understand or evaluate the application of any new
laser technique for use in
lithotripsy or other medical fields. Tissue optical properties and
laser parameters govern the mechanism(s) of fragmentation of urinary or
biliary calculi.
Laser pulse energies for clinical
lithotripsy range from Q0 = 20 mJ to 2 J for short-
pulsed lasers to long-
pulsed lasers, respectively.
Lasers with short pulse durations (i.e., less than a few microseconds) fragment
calculi by means of shockwaves following optical breakdown and plasma expansion of ionized water or
calculus compositions or by cavitation collapse, thus manifesting a photoacoustical effect.
Laser-tissue interactions involving dominant photomechanical or photoacoustical effects are usually stress confined. Long-
pulsed lasers (i.e., >100 microsec), on the other hand, generate minimal acoustic waves, and
calculi are fragmented by temperatures beyond the thresholds for vaporization of
calculus constituents, melting, or chemical decomposition.