Laser-induced acoustic stresses under submerged biological membranes

Er:YAG lasers are being widely studied as candidates for surgical procedures in liquid environments, such as in ophthalmology. However, while the Er:YAG laser can be a precise and efficient light scalpel, this surgical method includes accompanying stress waves that must be quantified and evaluated for potential harm. In this study, Er:YAG laser-induced stress waves for free running laser pulses were measured over various consecutive treatment periods. Using a spot-poled PVDF hydrophone, measurements were acquired beneath a biological membrane submerged in a saline bath. Results yielded pressures peaks of 300-600 mbar beneath the uncut membrane, which could be harmful for the optic nerve if located directly below the treatment area. Acoustic waves representative of direct laser-liquid interactions were observed immediately following membrane rupture, and yielded much larger pressures. The morphological changes in the acoustic wave can be used as a feedback signal to indicate when the membrane has been cut.