Metal Composite Nanomaterials And Ultrafast Photophysics Of Broadband Semiconductor Materials Research

In this thesis,first,we investigate the energy relaxation dynamics and third-order nonlinear optical susceptibilities of noble metal nanocomposites by using femtosecond(fs) pump-probe,time-resolved optical Kerr effect(OKE) and z-scan techniques.Then,multi-photon absorption processes in ZnO materials,including single crystal and microtubes,were studied under the excitation of intense fs pulses near 800 nm.Relative simulation has also been made.The main innovative results and conclusions are as follows:1.The energy relaxation dynamics and nonlinear optical properties of Ag:Si₃N₄ nanocomposite films fabricated by magnetron co-sputtering were investigated by utilizing fs pump-probe and z-scan techniques.After thermal treatment,the figure of merit was improved although the third-order susceptibility didn't change much.Heat treatment is proven to be a feasible way to improve the performance of ultrafast response for this material.The acceleration of the fast relaxation is attributed to the intensification of the coupling between the electrons and the phonons in Ag nanoparticles due to the diminishing of the detuning of the electron-oscillation phonon resonance overlap,caused by the size increase of Ag nanoparticles after annealing.The improvement of thermal conductivity properties of the Si₃N₄ substrate after annealing may be responsible for the acceleration of the slow relaxation process in the annealed samples.2.Effects of thermal treatment on the optical nonlinearity and ultrafast dynamics of Ag and Cu nanoparticles embedded in soda-lime silicate glasses were investigated.For the glass embedded with Ag nanoparticles,after the annealment,the figure of merit near the SPR increases obviously due to the increased content of Ag particles inside the glass.In addition to this,the relaxation is accelerated after the annealment,which could be attributed to the efficient interfacial coupling between hot electrons in Ag and phonons in SiO₂ substrate.The time-resolved experimental results indicate that the change of electrons population results in the red shift and the broadening of SPR,leading to the conversion from photobleaching to photoabsorption in the glass embedded with Cu nanoparticles.While Cu and Ag nanoparticles dominate the transient absorption properties of the nanocomposites at different wavelength in the glass embedded with both Cu and Ag nanoparticles.3.Multi-photon absorption in ZnO single crystal and microtube were investigated by utilizing intense fs pulses at wavelength near 800 nm.Nonlinear optical effects that may emerge under extremely intense field are attributed to be responsible for the efficient two-photon absorption process under detuned excitation.The simulation results of the two-photon Rabi effect show that there would be the population remained in the upper state if dephasing is taken into consideration even under detuning,while no population is found in the upper state after excitation when there is no dephasing effect.In conclusion,the ultrafast dynamics and the nonlinear optical response of metal nanocomposites were investigated.Heat treatment has been proven to be a feasible way to improve the performance of ultrafast response for this kind of materials. Based on the experimental results of ZnO materials excited by intense fs pulses near 800 nm,nonlinear optical effects that may emerge under an intense field are attributed to be responsible for the efficient two-photon absorption process under detuned excitation.Our research results are meaningful in accumulating the information of the optical properties of metal nanocomposite and the relative researches on the multi-photon absorption processes in ZnO materials are benefit for further understanding of the light-matter interaction under ultrashort intense excitation.