We report measurements of the dispersion in the linear optical properties (
linear absorption coefficient and refractive index) of polydiacetylene para
-toluene sulfonate (PDA-PTS) single crystal waveguide films prepared by the
rmal polymerization of the monomer free floating in solution and subsequent
attachment of the film to the substrate. A maximum absorption coefficient
> 10(5) cm(-1) at a wavelength of 620 nm is measured for polarization paral
lel to the polymer chains, in agreement with previous measurements. The ref
ractive index parallel to the polymer axis is significantly lower in these
thin films as compared to bulk PDA-PTS crystals, whereas the index perpendi
cular to the chains is comparable to that of bulk crystals. Sellmeier param
eters describing the dispersion of the refractive index in the near-infrare
d spectral range are given. (C) 2001 Published by Elsevier Science B.V.