Diazobenzene chromophore-doped silica films with large two-photon absorption cross-section

The diazobenzene chromophore, C.I Direct Red 28 (Congo Red) was modified using isocyanatopropyl silane and subsequently incorporated into a silica matrix, which significantly increased the thermal stability of the dye. The third-order nonlinearity of the ensuing hybrid dye-silica film was investigated using Third Harmonic Generation and Z-scan measurements at 1064 nm and 400 nm. The observed high, nonlinear refractive index (up to 10^-8 esu) of the film, as well as the large two-photon absorption cross-section at 1064 nm, was attributed to the enlarged and strengthened conjugated electron system as well as the symmetrical molecular structure of the hybrid material; optical Kerr studies showed that the hybrid films had an ultrafast response time of 0.36 ps at 400 nm.