欅田 英之

We performed sub-ps pulse-propagation experiments around the biexciton two-photon resonance in CuCl, and confirmed the soliton-like propagation of exciton-polariton pulses proposed by one of us [Phys. Rev. Lett. 75, 224 (1995)]. In our scheme two-photon nonlinearity compensates exciton-polariton dispersion, and pulse propagate without distortion. We compared our results with the calculated ones and obtained a good agreement between them.

We measured time-resolved photoluminescence on highly ordered and disorder films of polythiophene derivative, poly(3-[2-((S)-2-methylbutoxy)ethyl]thiophene]. A migration of self-trapped exciton (STE) is observed in both films, and a structural dependence of the STE behavior is revealed. (C)2000 Optical Society of America.

We performed propagation experiments of 150-fs optical pulses at the exciton resonance in CuCl. We observed several types of optical precursors corresponding to the Sommerfeld, the Brillouin, and the exciton precursors. (C) 2000 Optical Society of America.

We performed pump-probe transient absorption measurements around the exciton resonance in PbI(2) thin films. Coherent phonon oscillations corresponding to A(1) lattice mode were clearly observed at the excitation below the exciton resonance. (C)2000 Optical Society of America.

The time resolved photoluminescence experiments on highly ordered films of polythiophene derivative are reported to understand their excitation dynamics. Two films were prepared. One is a Langmuir-Blodgett (LB) film which contains almost 100% head-to-tail coupling of the side chain. Another is a spin coated film where each thiophene ring has the side chain at random position so that the collision of the side chains causes the torsion of thiophene rings. The high energy tail of luminescence is considered to arise from hot self trap excitons and that the slow red shift is caused by the migration of the self trap exciton to lower energy sites.

We performed sub-ps pulse-propagation experiments around the biexciton two-photon resonance in CuCl, and confirmed the soliton-like propagation of exciton-polariton pulses proposed by one of us [Phys. Rev. Lett. 75, 224 (1995)]. In our scheme two-photon nonlinearity compensates exciton-polariton dispersion, and pulse propagate without distortion. We compared our results with the calculated ones and obtained a good agreement between them.

We measured the spectra of the third-order optical nonlinearity, |χ(3)(ω;ω,ω,-ω)| around excitonic resonance in spincoated films and Langmuir-Blodgett (LB) films of polythiophene derivative, poly(3-[2-((S)-2-methylbutoxy)ethyl]thiophene), using the degenerate four wave mixing method. The value of |χ(3)(ω;ω,ω,-ω)| at the exciton resonance was approximately 10-7 esu, which was the largest value ever obtained in conjugated polymers.

2色のフェムト秒パルスを用いた非縮退型四光波混合測定を初めて成功させた。

Ionizing collisional loss rate of the metastable argon and krypton atoms in an optical lattice is compared with the rate of atoms in free space as a function of lattice laser detuning. Contrary to a simple picture of the isolation of atoms by the lattice potential, our experimental result shows that the collision rate in optical lattice is always larger than that in free space except at a large laser detuning of similar to 10(3) transition linewidth. Comparing the experimental result with the theoretical values that are derived from the classical trajectory calculation of the atom, we found that the optical pumping to non-trapped adiabatic potential surface prevents the collision suppression because it keeps the number of non-trapped atoms to a finite value even at low excitation rate.

Four-wave mixing (FWM) measurements around the exciton resonance are performed on the bilayer compound (C6H13NH3)2(CH3NH3)Pb2I7 to study the third-order optical nonlinearity. The values of |χ(3)(-ω ω,-ω,ω)| and dephasing energy at the exciton resonance are estimated to be 10-6 esu and 0.25 meV, respectively. The result of spectrally-resolved FWM in the cross-linearly polarized configuration shows that two-exciton state contributes to FWM signals for excitation below the exciton resonance.

The spectra of the third-order optical nonlinearity, \chi((3))(omega;omega,omega,-omega)\, around excitonic resonance in a spin-coated film and a Langmuir-Blodgett (LB) film of polythiophene derivative, poly(3-[2-((S)-2-methylbutoxy)ethyl]thiophene), were measured using the degenerate four-wave-mixing method. The obtained value of \chi((3))(omega;omega,omega,-omega)\ at the excitonic resonance was similar to 10(-7) esu, which was the largest value ever obtained in conjugated polymers. From the absorption spectra and \chi((3))\ spectra, the average effective conjugation lengths of the spin-coated film and the LB film were estimated to be approximately 20- and 36-thiophene rings, respectively. [S0163-1829(98)50144-0].

Third-order optical nonlinearity around the exciton resonance in (C6H13NH3)(2)PbI4 was measured using time-integrated and spectrally-resolved four-wave-mixing (FWM) techniques. For excitation below the exciton resonance, biexciton contribution to the FWM signals was observed. The dephasing energy of the biexcitons was estimated to be larger than 10 meV.

Third-order optical nonlinearity of regioregular head-to-tail coupled poly(3-hexylthiophene)(HT-PHT) was measured using degenerate four wave mixing (DFWM), and the dispersion spectrum of \X-(3)\ around the exciton absorption peak was obtained. In addition, the relaxation process of the excitons was measured using the transient grating method. The resultant decay time was less than 2 ps and consisted of two components.

無機有機複合型量子井戸物質において、励起子共鳴下で巨大な3次非線形性を発見した。

The enhancement of third-order optical nonlinearity in poly(3-hexylthiophene)(P3HT) by the control of regularity in the polymetric structure. The enhancement is due to increasing the conjunction length. The thin films of poly(3-[2-((S)-2-methylbutoxy)ethyl]thiophene)(P(S)MBET) is used which possesses large conjunction length. The |χ(3)| at excitonic resonance is measured using degenerate four-wave mixing (DFWM) and the conjunction length of samples are estimated.

The polarization-dependent four wave mixing (FWM) for excitation below the exciton resonance are measured to investigate the nonlinear optical response of excitons and biexcitons in a self-organized quantum-well material (C6H13NH3)2PbI4. The biexciton contribution to FWM signals is clearly observed. The FWM experiment is performed using a two-incident-beam configuration.

Third-order optical nonlinearity of regioregular head-to-tail coupled poly(3-hexylthiophene)(HT-PHT) was measured using degenerate four wave mixing (DFWM), and the dispersion spectrum of |χ(3)| around the exciton absorption peak was obtained. In addition, the relaxation process of the excitons was measured using the transient grating method. The resultant decay time was less than 2 ps and consisted of two components.

Third-order optical nonlinearity around the exciton resonance in (C6H13NH3)2PbI4 was measured using time-integrated and spectrally-resolved four-wave-mixing (FWM) techniques. For excitation below the exciton resonance, biexciton contribution to the FWM signals was observed. The dephasing energy of the biexcitons was estimated to be larger than 10 meV.

Ionizing collisional rate of metastable krypton and argon atoms in an optical lattice k(lattice) is compared with that in free space k(free). Reduction of the collisional rate is observed for krypton atoms. However, the magnitude of reduction is no more than a factor of 2 at the laser detuning of 7 GHz. The ratio k(lattice)/k(free) is found to change proportional to the square root of the excitation rate of atoms from the 1s5 metastable state to the 2p(9) state by the lattice laser. The mechanism that prevents a larger reduction is discussed.

Ultracold ionizing collisions of laser-cooled Kr isotopes in the 1s5[4p55s:3P2] metastable state are investigated. When the collision energy is reduced below the p-wave centrifugal barrier of 80 K, the ratio of the ionizing collision rate between polarized and unpolarized Kr83 atoms is found to decrease. This is a direct evidence of the quantum interference of two identical Fermi particles. The experimental results are compared with the calculation based on the simplified inelastic collision theory. © 1995 The American Physical Society.