An aluminophosphate glass system containing silver and tin was prepared by the melt-quenching technique in which spherical silver nanoparticles (NPs) of different sizes were embedded upon heat treatment. Optical absorption was used in the assessment of particle growth and for particle size estimation yielding mean radii in the 10–40 nm range. Measurements in the UV region revealed absorption features indicative of the occurrence of silver ions and twofold-coordinated tin centers. Photoluminescence spectroscopy excited at 355 nm showed a broadband emission around 420 nm for the non-heat-treated glass, which shows a thermal quenching effect in temperature dependence measurements. Heat-treated glass shows a dip in the emission spectrum ascribed to absorption by NPs. The luminescence is attributed to single Ag+ ions. The nature of the silver emitting states is discussed.

Laser-induced ultrafast nonlinear optical (NLO) response was observed in transient absorption, reflection and NLO measurements in VO2 thin films. The films were prepared using pulsed laser deposition technique with metallic vanadium and V2O5 powder employed as target material. The obtained thin films exhibit a thermal, as well as a laser-induced phase transition (PT) from semiconductor state at room temperature to metallic state. A typical hysterisis was observed for electric resistivity and optical reflectance verses temperature T. For the laser-induced PT in femtosecond pump–probe experiment, the PT was found to be ultrafast, immediately upon laser excitation. Kinetics study suggests that the PT is realized via an intermediate state, presumably a Wannier–Mott exciton (WME) state, followed by a resonant transition to the metallic phase state. The presence of the intermediate state is responsible for an extremely large third-order susceptibility observed in a nonlinear holographic experiment. In a 80nm thick VO2 thin amorphous film, the value of χ(3) was measured to be 1.3×10−8esu which is four orders of magnitude greater than a standard reference sample of CS2. In addition, the nonlinear response was further enhanced with diffraction signal increased by a factor of 4 after the laser excitation. A signal dip at ∼1.2ns was repeatedly observed, which is presumably due to the excitation process associated with the intermediate state. Finally, the resonant transition from the intermediate state to the metallic state, giving rise to a maximum diffraction signal intensity from the formed transient grating.

Light-induced insulator-to-metal phase transition of vanadium dioxide films was studied by ultrafast optical pump-probe spectroscopy. The transient optical reflection measurement shows that both heating and laser illumination contribute to the phase transition of VO2. Within 10−11–10−9 sec, these two mechanisms are competitive. Excited-state dynamics were found to be strongly dependent on the concentration of structural defects and the pump laser power as well. Comparison of the transient reflection of VO2 films deposited on different substrates suggests that the excitonic-controlled light-induced insulator-to-metal phase transition in VO2 proceeded through an intermediate state. The transient reflection measurement of VO2 in metallic phase shows a three-stage relaxation process. A polaron excitation model is introduced to describe the dynamical process for metallic VO2.

The nonequilibrium carrier dynamics in spherical silver nanoparticles embedded in aluminophosphate glass system was explored by femtosecond optical pump-probe technique. Photoluminescence and absorption spectroscopy were used for characterization of linear optical properties and particle size estimation. The two temperature model is employed to study the hot electron subsystem and evolution of electronic and lattice temperatures. The electron scattering dynamics on the 10-13-10-12 sec scale and two-photon absorption process are discussed. The laser-induced coherent vibrations of silver nanoparticles were observed in transient transmission experiments for relatively large particles with radii ~35 nm.

The nonequilibrium carrier dynamics in Ag nanoparticles was explored by femtosecond optical pump-probe spectroscopy. Metal-dielectric nanocomposite materials containing Ag nanoparticles of different sizes were prepared by thermal treatment of aluminophosphate glasses. The ultrafast relaxation dynamics of the electron scattering on the 10 −13 –10 −12 sec scale shows size-and pump power-dependent properties. The two-photon absorption process in nanoparticles of different sizes is discussed. The laser-induced coherent vibrations of nanoparticles were observed in transient transmission experiments.

Insulator-to-metal phase transition (PT) and relaxation dynamics in VO 2 were studied with ultrafast transient reflection spectroscopy and degenerate four wave mixing technique. Optical pumping of free carriers in VO 2 initiates PT on a femtosecond time scale. The relaxation dynamics is strongly dependent on pump energy. Spectral reflectivity behaviour at PT due to thermal heating and upon laser excitation of VO 2 demonstrates close proximity in the relative change. PT induced by light was interpreted by exciton-controlled mechanism. Excited state dynamics of metallic VO 2 is assigned to formations of electronic and hole polaronic states.