Sol-Gel Preparation and Nonlinear Optical Properties of Transition Metal Oxide Thin Films

Abstract

Several transition metal oxide thin films have been prepared on SiO₂ glass substrates by the sol-gel method and their nonlinear optical (NLO) properties have been examined on the basis of the third harmonic generation (THG) method. It was found that for transition metal oxides with empty d-orbitals the third order nonlinear optical susceptibility χ⁽³⁾ increases with decreasing M–O bondlength. This phenomenon was explicable in terms of Lines’ bond orbital theory. On the other hand, iron oxides with partially filled d-orbitals exhibited quite high χ⁽³⁾ of the order of 10⁻¹¹–10⁻¹⁰ esu, which was considered to be due to the pair excitation process involving the simultaneous excitation of magnetically coupled two neighboring Fe³⁺ ions. Second hyperpolarizability γ of various metal cations was estimated from our results, which is a measure of microscopic NLO properties of individual constitutional melal cations.