Treatment of benign prostate hyperplasia to restore proper urination. Pulsed lasers can deliver energy very rapidly to a target. When a target is heated, there is a thermoelastic expansion of the target which causes a rise in pressure within the target. Stress confinement refers to the process of causing a pressure rise in a target before the pressure can dissipate from the target at the speed of sound. Such a pressure causes a target to explode.
Spallation is another photomechanical event.
The expansion is positive pressure or stress but the snap-back is negative stress. A thin layer of tissue is ejected. Such internal breaks are called spall planes , or in liquids or soft tissues they are called cavitation bubbles . This is the same cavitation phenomena elicited in water by the prop of a motor boat. Another photomechanical event involves phase changes such as vaporization or plasma formation.