Transient Changes of Optical Properties in Semiconductors in Response to Femtosecond Laser Pulses

In this paper we present an overview of our theoretical simulations on the interactionof ultrafast laser pulses with matter. Our dedicated simulation tool, X-ray induced Thermal AndNon-thermal Transitions (XTANT) can currently treat semiconductors irradiated with soft to hardX-ray femtosecond pulses. During the excitation and relaxation of solids, their optical properties suchas reflectivity, transmission and absorption, are changing, affected by transient electron excitationand, at sufficiently high dose, by atomic relocations. In this review we report how the transient opticalproperties can be used for diagnostics of electronic and structural transitions occurring in irradiatedsemiconductors. The presented methodology for calculation of the complex dielectric functionapplied in XTANT proves to be capable of describing changes in the optical parameters, when thesolids are driven out of equilibrium by intense laser pulses. Comparison of model predictions withthe existing experimental data shows a good agreement. Application of transient optical propertiesto laser pulse diagnostics is indicated