Yusaburo Segawa

Optical limiting performance of a novel σ–π alternating polymer

Abstract Nonlinear optical absorption and optical limiting behavior of a novel σ – π alternating polymer, poly(disilanylene-2,2′-bipyridine-5,5′-diyl) ruthenium complex were evaluated with nanosecond pulses at 532 nm. The limiting throughputs at three concentrations were investigated. The experimental results indicated that this sample is very efficient as an optical limiting material. Using the standard Z -scan technique, we obtained the effective two-photon absorption coefficient. The theoretical fits to the data give a value of β =3.5 cm/GW.

Conductivity of fullerene-doped optical glasses

Appropriate amount doping of fullerenes caused insulating phosphate and fluorophosphate optical glasses to be conductive at room temperature. Microphotoluminescence measurements indicated the existence of ordered and disordered microstructures. A large number of fullerene-related medium-range microdomains aggregated as self-organized islands along the glass networks, and brought about connective tissues in the vitreous matrices for percolation migration of metal cations. The variation of microphotoluminescence induced by electric field presented us an indirect way to characterize the random activation, percolation migration, and retrap of metal cations near fullerene-related amorphous islands.

Optical limiting and bistability of a σ–π photoconductive copolymer

Abstract Optical nonlinearity of a σ–π photoconductive copolymer, poly(disilanylene-2,2 ′ -bipyridine-5,5 ′ -diyl) ruthenium complex, has been investigated in chloroform solution of various concentrations. The nonlinear optical absorption resulted in optical limiting, optical bistability, and laser pulse compression for nanosecond pulses at the wavelength of 532 nm. Theoretical analyses showed that the optical absorptive nonlinearity was dependent on the photogenerated excitons and exciton–exciton couplings.

Excimer-like emission of a novel sigma-pi alternating polymer with 2,2?-bipyridyl in the backbones

The luminescent properties of a novel - polymer, poly(disilanylene-2,2´-bipyridine-5,5´-diyl) ruthenium complex (PDSBpy-Ru), have been investigated. A tetrahydrofuran solution of PDSBpy-Ru exhibits fluorescence with peaks dependent on the solution concentration. In a dilute solution, single PDSBpy-Ru molecules are excited, generating metal-to-ligand charge transfer excitons (or electron-hole pairs). The corresponding charge recombination produces fluorescence emission with a peak at about 650 nm. On excitation of a tetrahydrofuran solution of PDSBpy-Ru with a higher concentration, a linear PDSBpy-Ru molecule forms an excimer-like adduct with a neighbouring PDSBpy-Ru molecule. The excimer-like adduct emits fluorescence with redshifted peaks.

Scanning second-harmonic microscopy of a thin film of sigma-pi copolymer with 2,2'-bipyridine in the backbone

Scanning second-harmonic microscopy was used to study the lateral distribution of the second-order optical nonlinearity of a - copolymer [poly(disilanylene-2,2-bipyridine-5,5-diyl) ruthenium complex (PDSBpy-Ru)] thin film on a glass substrate. The orientation of the dipolar chromophores and establishment of the noncentrosymmetry required by the macroscopic second-order optical nonlinearity were resulted from natural coordination of the PDSBpy-Ru molecules to the surface Si-O-H groups on the glass substrate. A homogeneous lateral distribution of the coordination-induced poling was observed.

Dynamics of photo-induced phase-transition in low dimensional organic crystals and the role of photocarriers

We report the dynamics of a unique photo-induced phenomenon in quasi-one-dimensional organic crystals; i. e. phase transitions triggered by photo-excitation in conjugated polymers and charge-transfer crystals. Nano-second and pico-second time-resolved studies indicate that photo-generated charge-carriers (bi-polarons) play an important role in the driving process of the photo-induced phase transition (PIPT)

Motional displacement and entanglement of a trapped ion

The first sideband Raman excitations driven by counter-propagating Raman beams are analysed for the trapped ion under the localization condition in or beyond the Lamb-Dicke regime. It is demonstrated that multiquantum processes in the vibrational couplings produce significant effects on the the first sideband Raman transitions and the relevant Raman displacements for the trapped ion beyond the Lamb-Dicke regime. The quantum features of the vibrational states attained by displacing the motional ground state are demonstrated to be closely associated with the nonlinear vibronic couplings. Quantum entanglement, and quantum interference as well, are discussed for ion traps with various Raman excitation and localization conditions. The results are compared with the recent experiment reported by Monroe C et al in 1996 Science 272 1131-5.