Time-resolved studies of Nd:YAG laser-induced breakdown. Plasma formation, acoustic wave generation, and cavitation.

The use of high intensity ultrashort pulsed laser radiation to produce optical breakdown is an important approach for the surgical treatment of intraocular structures. We have investigated the transient properties of Nd:YAG laser induced breakdown in a saline model using time-resolved spectroscopic techniques. Spatially resolved pump and probe techniques are applied to study the dynamic behavior of the plasma formation, acoustic wave generation, and cavitation processes which accompany the optical breakdown. Measurements of plasma shielding and luminescence indicate that the laser induced plasma forms on a subnanosecond time scale and has a lifetime of several nanoseconds. An acoustic transient is generated at the breakdown site and propagates spherically outward with an initial hypersonic velocity, then loses energy and propagates at sound velocity. Transient heating following the plasma formation produces a liquid-gas phase change and gives rise to cavitation or gas bubble formation. This gas bubble expands rapidly for several microseconds, then slows to reach its maximum size and finally collapses.