Femtosecond reflectance spectroscopy of a rarefaction wave front

Summary form only given. Intense femtosecond irradiation of a solid surface creates transient (/spl sim/ Mbar) internal pressure because the lattice is heated faster than thermal expansion can occur. Before the pressure is released, the heated surface remains optically sharp and time-resolved ellipsometric measurements can be analyzed with Fresnel´s equations. At later times (/spl delta/t > 1/spl sim/2 ps), a rarefaction wave front develops at the surface, as the laser-induced strong compressional shock wave acts on the solid density plasma. The expansion dynamics can provide diagnostic information on initial pressure-temperature conditions. This expanding rarefaction wave front can also be probed by time-resolved ellipsometry measurements, provided they are analyzed by generalized Helmholtz wave equations. The authors report comprehensive measurements on free electron metals (AI), semiconductor (Si), and semimetal (graphite) targets using variable probe incidence angle, wavelength, and polarization.