2. The proposed reaction mechanism for the laser-induced reaction of C12 with Al surface mainly consists of the dissociative chemisorption of C12 on the aluminum surface, diffusion of chlorine into the bulk, the reactions of adsorbed C1 atoms with A1 and chlorides, and the laser-induced desorption of the reaction products. The reaction is driven directly by the incident C12 molecular beam with high translational energy,and the role of pulsed laser irradiation is mainly to induce desorption.3. The 1064-nm photons cause thermal desorption of A1C13 via the laser thermal heating effect, and the TOF spectra of the desorbed species can be fitted by a Maxwell-Boltzmann distribution. Both thermal and nonthermal desorption processes exist for the 355-nm case. However, the precise mechanism for the nonthermal desorption, such as electronic excitation and/or laser-induced plasma, should be further investigated.Photoinduced ahsorption on the high-energy side of the Q-band has been observed and timeresolved in polycrystalline/amorphous thin films of both fluoroaluminum and chloroaluminum phthalocyanine. The films were pumped with =lOO-fs optical pulses at various wavelengths inside the inhomogeneously broadened Q-band, including 620 and 760 nm. The induced absorption signal is accompanied by a bleaching signal on the low-energy edge of the Q-band. The bleaching signal resembles a blueshifted monomer absorbance spectrum. The induced absorption signal develops as the absorption bleaching signal decays, suggesting exciton decay into a subgap state. The different bimolecular decay dynamics observed for the absorption bleaching ( T~~ = 700 fs) and induced absorption (reW = 2 ps) signals support this conclusion. Analyses of the results and possible origins of the indicated subgap state are discussed.

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The linear and nonlinear optical properties of commercially available CdS.,Se l _ x doped glasses are reviewed and the origin, magnitude, and temporal response of the nonlinearities are discussed . The room-temperature carrier dynamics are analysed using femtosecond interband pump-probe measurements . Our experimental results show the evolution of the carriers into a hot, quasi-thermal plasma distribution via electron-electron and electron-phonon scattering . The quasi-thermal distribution cools to the lattice temperature in about 750 fs filling the states just above the band-edge . This band-filling nonlinearity is seen as the bleaching of the absorption above the bandedge . The carrier recombination lifetime is measured to be =10 ps at higher carrier densities . IntroductionIn this paper, we review the optical nonlinearities of composite semiconductor/ host materials that are composed of a fractional volume percentage of small semiconductor particles embedded in an insulating dielectric host . The semiconductor microcrystallites are smaller in size than an optical wavelength so that the composite material appears optically homogeneous . Examples of such composite materials are silicate glasses doped with semiconductor microcrystallites or semiconductor colloids [50][51][52][53][54][55][56][57][58][59][60] . Since these composite materials are macroscopically isotropic, second-order nonlinearities are usually non-existent, and technical interest focuses on their third-order nonlinearities which are essential for applications in optical signal processing . This paper addresses the dynamics of the bandfilling nonlinearity in commercially available borosilicate glasses doped with CdSxSel _ x microcrystallites of 100 to 1000A .

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