Published online by Cambridge University Press: 16 February 2011
A second order nonlinear optical susceptibility inversion structure in the thickness direction (NIST) is proposed for enhancing the efficiency of Cerenkov radiation type phase matched second harmonic generation (CRPM-SHG). With the aid of the coupled-mode theory, it is analyzed that the efficiency is enhanced by 50 to 100 times by introducing the NIST structure to a waveguiding layer made of a 2-docosylamino-5-nitropyridine (DCANP) Langmuir-Blodgett (LB) film, and that the optical conditions for the most efficient CRPM-SHG are equivalent to those for guided mode SHG at the cutoff points of the modes. Several fabrication methods are possible for NIST waveguides. For the first time, a NIST waveguide has been fabricated using a DCANP-LB film by employing a novel and simple technique in which the substrate inversion is carried out during the dipping process. The inversion in nonlinearity was confirmed using the maker fringe method and polarized absorption spectra. A NIST planar waveguide of 260 Monolayers of DCANP (570 nm thick) was fabricated. Intense CRPM-SHG was observed from the waveguide when a YAG laser was coupled into it. The intensity was 20 to 30 times larger than that of a conventional waveguide of the same thickness.