A Theoretical Study of the Refractive Index of KDP Crystal Doped with TiO2 Nanoparticles

Abstract

In the present chapter we study a nonlinear response of an optical matrix formed by the K2HPO4 crystal doped with TiO2 nanoparticles. Such doped matrix is a nonlinear optical system that is characterized by the cubic non-linear optical response at picosecond laser pulses. Laser pulses release photoelectrons from nanoparticles, which emerge as free carriers on the nanoparticles' surface generating an electric field in local area of the K2HPO4 matrix, which results in the phase transition from the paraphase to the ferroelectric phase state. The appeared ferroelectric phase induces a large polarization around TiO2 nanoparticles, which in turn immediately produces a nonlinear optical response to the laser pulse of the inverse sign, such that the laser beam becomes more focused. The gigantic non-linear susceptibility ??(3) responsible for the phenomenon of focusing of the laser beam is calculated by using the pseudospin model for the description of ferroelectric crystals and the expressions for nonlinear-susceptibility tensor components computed by other researchers.