Highly sensitive detection of transient absorption in dye-doped ultrathin polymer films by the TiO(2)/K(+) composite optical waveguide method upon pulsed laser excitation.

A composite optical waveguide (OWG) composed of a 10-18nm thick titanium dioxide (TiO(2)) film sputtered on a conventional K(+)-doped optical waveguide was first applied to detect transient absorption of organic dyes in ultrathin polymer films upon excitation with ns laser. The thickness of the TiO(2) film considerably affected the relative sensitivity of the composite OWG. The composite OWG with 10nm thick TiO(2) gave much stronger transient absorption for 30-415nm thick polymer films containing organic dyes than that with 18nm TiO(2). Transient absorption of phthalocyanine and spiropyran in 20-135nm thick polymer films was detected 3-20 times more sensitively by the composite OWG with 10nm TiO(2) than the conventional K(+)-doped OWG which showed a 150-fold sensitivity as compared with the usual normal incidence method. The relative sensitivity of the composite waveguide was also affected by the thickness and refractive index of polymers.