Periodically domain inverted poled polymer film by two-step poling

We report the fabrication technique for domain inverted polymer film. A two-step process of corona poling and contact poling is presented. PMMA containing disperse red 1 was spin-coated on ITO layer of a soda-lime glass substrate. Al electrode was deposited on the polymer film. Periodically poled structure was created by the preceding contact poling. The film was heated slightly below the polymer glass transition temperature. Negative voltage was applied to the Al electrode across the film to the ITO layer. The major drawback of the quasi-phase matched (QPM) SHG technique is the presence of large scattering loss at domain walls due to refractive index mismatch caused by different poling strength in neighboring domains. Multiple reflection results in loss accumulation. The condition of the corona poling was optimized not only to minimize depoling in the contact-poled region but also to obtain matched poling strength. Two types of samples, a periodically poled film and a periodically inverted film, were prepared to confirm presence of domain inversion. Distribution of second-order-nonlinearity is shown. The second harmonic (SH) wave intensity was measured. We compare the SH distributions between the two samples. It is evident that SH waves generated in the neighboring antiparallel domains counteract each other. The actual length of the transition region was presumably smaller since the diameter of the fundamental beam was nearly 1 mm. We are developing the two-step poling process to obtain fine structure of domain inversion to achieve QPM-SHG.