Analysis and control of heat transfer in laser induced thermal poling process of polymer thin film

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We have focused on the development and the optimization of waveguide patterning process in nonlinear optical (NLO) polymer thin film by laser induced thermal poling. In this research, we have elucidated the following subjects.1) Measurement of the thermal diffusivity of NLO polymer thin film.Thermal properties of NW polymer are an important factor in the thermal poling process. To measure the thermal diffusivity of the nonlinear optical (NW) polymer thin film, we modified the experimental apparatus based on the photoacoustic method. PMMA with DR1 chromosphore side groups was synthesized as an NLO polymer. It was found that the thermal diffusivity is independent on film thickness and percentage of the chromosphore, but increases as the applied electric field increases. Also, the thermal diffusivity of the NLO polymer thin film decreases with temperature. Our apparatus has no capability to measure at high temperature, more than glass transition temperature (about 380K) which gives abrupt … More ly change in thermal diffusivity, It is desired to develop another method to measure thermal diffusivity at high temperature.2) Numerical simulation of laser induced thermal poling processWe have constructed three-dimensional simulation code to estimate temperature profile in NW polymer thin) film on thermal poling process. To elucidate optimized condition for uniform polarization profiles, we introduced the temperature dependence of dipole (in NLO molecule) orientation dynamics to our simulation code. Since there is no available model for dipole orientation dynamics, relaxation dynamics model was used. At first, Ar^+ laser (wavelength of 488 nm) was used as light source on simulation. The calculation results showed that smaller diameter of laser beam and slower scanning speed of laser give more uniform polarization profiles. Since absorption spectrum of thin film suggests that He-Ne laser (wavelength of 632 nm) illuminates the thin film more interior than Ar^+ laser, He-Ne laser results in higher and more uniform polarization profiles. It is necessary to measure the dipole orientation dynamics for polymer materials in an electric field. Less