Material glass-transition temperature, device thickness and operational temperature effects on absorption of electro-optic polymer films

In chromophore doped materials, the trade-off between nonlinear coefficients and absorption is a critical issue. In particular, χ⁽²⁾:χ⁽²⁾ cascading based applications at 1.55 μm impose stringent conditions on the absorption at the second-harmonic wavelength. Transmission spectroscopy through a thin film does not provide sufficient resolution to measure the absorption coefficient on the red side of the main absorption band. However, assuming Voigt profiles, it is possible to extrapolate the absorption coefficient in the near infrared (NIR) from the main electronic resonance. We report on the dramatic impact of the host polymer matrix on the near infrared absorption of azobenzene chromophores. The effect is directly correlated to the host polymer glass transition temperature. The case of hybrid sol-gel material is also discussed. In particular, we present here an interesting correlation between the poling temperature and some spectroscopic properties. This correlation and thermo-spectroscopic measurements lead us to define an effective T_g in the sol-gel system. We also report on film thickness dependent absorption properties.