Study on nonlinear optical properties of N+ ion implanted poly-o-toluidine films

Poly-o-toluidine (POT) was synthesized chemically using (NH4)2S2O8 as oxidizing agent in acidic media. The POT films were prepared by spin-coating method with a thickness of about 300 nm and implanted by 35 keV N+ ions with the dose in the range of 6.3 × 1013 to 7.6 × 1016 ions/cm2. The POT films in pristine and implanted forms were characterized by visible absorption spectra, which showed that the optical absorption in the visible band was reinforced by ion implantation. The optical band gap (Eg) of POT film derived from the visible absorption spectrum was decreased from 3.3 to 2.59 eV with the increase of ion dose. The effect of ion implantation on third-order nonlinear optical (NLO) susceptibility (χ(3)) was investigated carefully by degenerate four-wave mixing (DFWM) technique. The χ(3) value of pristine POT film was 3.27 × 10−10 esu and the maximum χ(3) value of implanted POT film was increased to 3.56 × 10−9 esu when the ion dose was 1.9 × 1016 ions/cm2.