Photoinduced molecular orientation in bulk azodye-doped polymer by nonresonant femtosecond laser pulses

Abstract

We show two kinds of photoinduced molecular orientations in bulk azodye-doped polymers: photoinduced molecular orientation with centrosymmetry and photoinduced molecular orientation with noncentrosymmetry. For the photoinduced molecular orientation with centrosymmetry, the samples were irradiated with a linearly polarized femtosecond laser whose wavelength (800 nm) was out of the absorption range of the azodye molecules. This photoinduced molecular orientation with centrosymmetry resulted in a birefringence in the sample, based on which an optical image storage was demonstrated. The probe transmittance for the induced birefringence was estimated to be 92%. For the photoinduced molecular orientation with noncentrosymmetry, the sample was irradiated simultaneously by coherent superposition of the 1500-nm fundamental and 750-nm second-harmonic light of a femtosecond laser. The second-harmonic generation (SHG) conversion efficiency of a 105-μm thick film was estimated to be about 2%.