Induced Absorption in Silicon under Intense Laser Excitation: Evidence for a Self-Confined Plasma

Time-resolved transmission and reflectivity of silicon on sapphire have been studied at $\lambda =1152\mathrm{} \mathrm{and} 633$ nm following excitation by a ∼1 J/${\mathrm{cm}}^2$, 8 nsec pulse at 485 nm. In addition, the spectral dependence of the transient absorption was obtained for the range 1.3 to 3.3 eV with use of a pulsed-dye-laser probe. The results are inconsistent with a metallic molten state but suggest the existence of a self-confined dense carrier system similar to that proposed by Van Vechten and Wautelet.