Abstract

Intense femtosecond irradiation of a solid surface creates transient (~1 Mbar) internal pressure in the absorption region because the lattice is heated faster than thermal expansion can occur. Before the pressure is released (Δt ~ 1-2 ps) the heated surface remains optically sharp, so that time-resolved ellipsometric measurements can be analyzed with Fresnel’s equations, revealing the optical properties of novel pressurized fluids such as liquid carbon.^1,2 At slightly later times (2 ps < Δt < 20 ps) a strong compressional shock wave propagates into the bulk, while a trailing rarefaction wave develops at the surface. The expanding rarefaction wave front can also be probed by time-resolved ellipsometry measurements, provided that they are analyzed by generalized Helmholtz wave equations.⁹ We recently presented preliminary time- resolved reflectivity measurements of hydrodynamically expanding metal surfaces in which we used a single probe wavelength (620 nm) and incidence angle (70°).

© 1993 Optical Society of America