Abstract

Polysilanes are long σ-bonded Si-backbone polymers with various organic side groups substituted onto each Si atom. Films and waveguides of high optical quality can be easily fabricated using conventional photoresist coating technology. These materials are transparent throughout the visible spectrum but have large (α ≈ 25,000-cm⁻¹) UV absorptions and large optical nonlinearities. Exposure of films of poly(di-n-hexylsilane) to weak doses of polarized UV light causes selective scission of chains with dipole moments aligned with the polarization of the exposing light, inducing a weak birefringence. Exposure to larger doses causes complete photovolitilization of the film. Higher birefringence from selective chain scission can be obtained using the large two-photon absorption observed in these materials [χ⁽³⁾ for the process is ≈10⁻¹⁰ esu]. Photoexposure at ≈15 MW/cm² with wavelengths corresponding to twice the UV absorption produces a birefringence proportional to exposure saturating at Δn ≈ 0.03. No photovolitilization was observed; thus with films several microns thick, the exposed films could be used as waveplates with phase delays as large as λ/4. We have also used this two-photon-induced chain scission to produce polarization sensitive gratings using a standard holographic arrangement. Diffraction efficiencies as large as 1% were observed for light polarized parallel to the exposing radiation, while no diffraction was observed for orthogonally polarized light.

© 1988 Optical Society of America