Using multiphoton absorption with high-intensity lasers to heat transparent liquids

Most pure, organic liquids are remarkably transparent materials, even when exposed to high laser intensities. At very high laser intensities, however, similar to 10(9)-10(10) W/cm(2) and under the appropriate conditions, liqu ids can absorb extremely strongly due to the mechanism of multiphoton absor ption, which results in ionization and dissociation of the liquid molecules . Strong absorption results in significant heating and temperature increase s. Multiphoton absorption thus provides a new mechanism for heating otherwi se transparent liquids. Furthermore, the thermal energy is deposited in a v ery thin layer near the surface of the liquid, which is much thinner than t he classical penetration depth. A thermal model based on multiphoton absorp tion is developed, and results are presented for heating liquid water with laser pulses from the popular Nd: YAG laser at a wavelength of 266 nm.