S. Iwai

Subpicosecond dynamics of confined excitons and optical nonlinearities of CuCl quantum dots

Abstract We have investigated the dynamics of confined excitons and their optical nonlinearities in CuCl quantum dots embedded in NaCl and glass matrices using subpicosecond band-to-band excitation. The quantum dots in the glass matrix exhibit a smaller blue shift of the exciton bands and much weaker optical gain due to biexcitons.

Subpicosecond dynamics of confined excitons in CuCl nanocrystals

We performed subpicosecond pump-and-probe measurements of CuCl nanocrystals at 77 K using a UV pump light of moderate intensity and high repetition rate and also a UV white probe light. For CuCl nanocrystals embedded in a glass matrix and in an NaCl matrix, we compare the temporal behavior of the non-linear change in the confined exciton absorption band induced by the existence of one exciton per nanocrystal. The decay time of the non-linear change is found to be much faster in the glass matrix than in NaCl, reflecting shortening of the exciton lifetime due to the photofatigue effect.

Nonlinear Optical Spectra of the Confined Excitons in Stress Induced Nanostructures in BiI3

We report the optical nonlinear response of the confined excitons in nanostructures induced by external stress in a layered crystal BiI3. The absorption intensity of the confined excitons is saturated by intense laser excitation. We clarify the size dependence of the saturation density which reflects the nanostructure size. The saturation density of the confined exciton in large domains is lower than the the case of small domains. By pump-probe measurements using a sub-picosecond laser pulse, we examine the dynamical process of the confined excitons in the disks with various sizes. From the temporal behavior of the absorption saturation, it becomes clear that the exciton life times in small disks are shorter than the large ones. A new nonlinearly growing luminescence due to the process by a inelastic recoiling of excitons is detected.

Picosecond Dynamics of Confined Excitons and Their Optical Nonlinearities in CuCl Nanocrystals

Optical nonlinearities in confined exciton system were investigated in CuCl nanocrystals embedded in NaCl matrices at 77 K with use of ns and sub-ps laser excitations. Size-dependent excitation photon density necessary for the saturation of the exciton absorption peak under the ns excitation at the exciton resonance showed that the number of excitons per one nanocrystal governs the magnitude of the saturation regardless of the crystal size. Transient absorption change measured under sub-ps band-to-band excitation revealed the strong correlation between the temporal response of the excitonic optical nonlinearities and the formation and decay dynamics of the exciton and biexciton systems in CuCl nanocrystals.

Ultrafast terahertz response driven by photoinduced insulator to metal transition in layered organic salt

Photo-induced insulator to metal transition in two-dimensional organic salt α-(ET)2I3 (ET: [bis(ethylenedithio)]tetrathiafulvalene) was investigated by near-IR-pump and THz-probe spectroscopy. Photo-induced microscopic and semi-macroscopic metallic domains were characterized by a transient THz spectrum.