Quasiphase-matched second-harmonic generation using periodically photoisomerized azo dye doped polymer film waveguide

A process to form a periodically poled polymer film by photoisomerization is described. A poled film of polymethylmetaclyrate containing 5 wt % of 4-(4-nitrophenylazo)aniline (Disperse Orange 3) was exposed to an Ar⁺ laser beam using a photomask of a 100 μm period grating. Disorientation of the chromophore molecule resulted in decrease of d₃₃ in the photoisomerized domain. Quasiphase-matched second-harmonic generation is demonstrated experimentally using a processed film. Phase-matching was confirmed by tuning the fundamental wavelength around 1200 nm. The effective propagation length due to a tightly focused fundamental wave and the influence of the absorption loss are discussed. The depoling process by photoisomerization is compared with photobleaching, optical poling, and electron beam treatment.