Abstract

The challenging requirements of future all-optical signal processors have stimulated the investigation and characterization of nonlinear materials, such as polydiacetylenes, that are expected to exhibit large off-resonance electronic values of χ⁽³⁾ in the telecommunications windows. Among them, the polycarbazolyldiacetylene DCHD-HS exhibited solubility in common organic solvents and allowed fabrication of films and waveguides [1]. The intensity-dependent refractive index of thin polyDCHD-HS films (10 ÷ 50 nm) deposited on silver layers was measured at 1064 nm with picosecond pulses and using Surface Plasmon Spectroscopy (SPS) [2]. A surprisingly large variation was observed which was not confirmed by independent nonlinear measurements performed by Z-scan with solutions and by Third Harmonic Generation in the solid state [3]. The aim of this work is to understand the origin of the anomalous nonlinear behavior observed with SPS experiments. To this end, we describe at first the SPS measurements and, subsequently, the Surface Enhanced Raman Scattering (SERS) experiments with films of different thickness (10÷200 nm).

© 2002 Optical Society of America