title: Fragmentation process of current laser lithotriptors.
abstract: OBJECTIVE
  Flashlamp pumped dye (FPDL), Q-switched Nd:YAG, and alexandrite lasers are the most clinically used laser lithotriptors. Although calculi are fragmented by laser induced mechanical stresses for all lithotriptors, different fragment sizes and fragmentation efficiencies have been reported. In this work the effect of the pulse duration and pulse shape on the fragmentation processes is studied.
  
  
  METHODS
  Fragmentation processes are characterized on model stones and on sensing target fibers. Stone fragmentation and cavitation bubble generation are observed by video flash photography. Shock wave occurrence and strength are monitored with an hydrophone.
  
  
  RESULTS
  For the FPDL, stone fragmentation is induced by the collapse of the large cavitation bubble formed. For the Q-switched Nd:YAG, fragmentation is already observed during the laser pulse, at the plasma onset, although further fragmentation can occur at the bubble collapse. For pulse durations corresponding to the alexandrite, an intermediate fragmentation regime is observed.
  
  
  CONCLUSIONS
  For the first time the physical basis of the observed differences in the fragmentation efficiencies of current laser lithotriptors is described. For nanosecond durations the fragmentation processes are governed by plasma induced shock waves. On the contrary, for microsecond durations fragmentation is governed by cavitation. The high fragmentation efficiency of microsecond lasers is due to a high laser energy transfer into cavitation.
authors.affiliation: Laboratoire d'Optique Appliquée, Ecole Polytechnique Fédérale de Lausanne, Switzerland.
authors.forename: K
authors.initials: K
authors.lastname: Rink
authors.forename: G
authors.initials: G
authors.lastname: Delacrétaz
authors.forename: R P
authors.initials: RP
authors.lastname: Salathé
mesh_terms: D066298:In Vitro Techniques; D017602:Lithotripsy, Laser / Q000295:instrumentation; D008422:Materials Testing; D008962:Models, Theoretical; D011312:Pressure; D012822:Silicon Dioxide / Q000528:radiation effects; D013314:Stress, Mechanical; D013718:Tensile Strength; D014545:Urinary Calculi; D014741:Video Recording
chemical_list: D012822:Silicon Dioxide