Phase-matched second-harmonic generation in cross-linking polyurethane films by thermal-assisted optical poling

Abstract

Phase-matched second-harmonic generation (SHG) in thermal-cross-linking polyurethane films was demonstrated using a thermal-assisted nonresonant optical poling technique. During the seeding process, samples heated in an oven were irradiated simultaneously by coherent superposition of the 1300nm fundamental and 650nm second-harmonic lights of a femtosecond laser. The photoinduced second-order optical nonlinearity of the polymer films seeded at elevated temperatures kept stable at room temperature. The measurements for the dependence of SHG on the film thickness showed that a χ(2) grating that satisfied the phase-matching condition for SHG was optically induced in the polymer films.