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Takayoshi Kobayashi Laboratory,Advanced Ultrafast Laser Research Center

Introduction of our laboratory


OPAL-RING

Research Subjects:

Ultrafast and Nonlinear Optical Processes, Quantum Optics, Quantum Photobiology

In order to evaluate ultrafast nonlinear optical susceptibilities of optoelectronic device materials, we develop new methods for time-resolved nonlinear spectroscopy and measure time dependence of optical nonlinearities. On the basis of these measurements we clarify mechanisms of nonlinearities, and give guiding principles for designing new optoelectronic devices.

  1. Development of ultrashort pulse lasers
    1. Generation of shortest 4.7fs visible pulses by noncollinear optical parametric amplifier (NOPA): World shortest pulses in the visible was obtained by two sets of carefully designed chirped mirrors and a prism pair.
  2. Sub-5-fs real-time spectroscopy
    1. Polydiacetlenes: A high-frequency multi-mode wavepacket motion with the three carbon-carbon stretching modes and chain-deformation modes was observed. The highly vibronic non-equilibrium in the relaxed state characterized by the mode frequency and amplitude modulations is well explained by non-adiabatic coupling of the stretching and bending modes in the butariene-like backbone. This is the first real-time observation of coupling between normal modes.
    2. Dye molecules/polymer film: Self-induced modulation of vibration in dye molecules doped in a polymer film was observed using sub-5-fs pulses. The modulation of potential curves was obtained from the frequency and amplitude modulations of the observed vibrational mode.
    3. J-aggregates: Sub-5-fs real-time spectroscopy revealed that coherent molecular vibrations coupled to the Frenkel exciton system. The oscillation in the induced absorption spectrum is interpreted as the modulated transition dipole moment due to the oscillator strength transfer.
    4. Quasi-one-dimensional halogen-bridged mixed-valence metal complex: Wave packet motions both in ground and self-trapped exciton (STE) states are observed as oscillatory modulations. The energy relaxation rate of the non-thermal STE is determined. The onset of the wave packet motion is delayed after the photo-excitation on the STE potential surface. This delay time is attributed to the internal conversion between free exciton and STE states.
  3. Development of new measurement system
    1. Multiplex method for nonlinear susceptibility spectrum measurement: Continuous spectrum of nonlinear susceptibility can be measured by single shot using this system. The spectrum of the third-order nonlinear susceptibility of polydiacetlenes was measured and the energy of 21Aglevel were able to be determined by that spectrum.
    2. System of time-resolved spectroscopy in mid infra red region: Ultrashort pulse laser in mid IR was constructed by optical parametric amplifier. The spectrum region was 5μm-8μm. The pulse width was determined as 400fs by pump-probe signal of Si.
    3. Scanning near-field optical microscope(SNOM): In order to observe an optical nonlinearity of a single J-aggregate, a SNOM has been constructed. Both fluorescent and absorption spectra are successfully observed with a special resolution more than 100nm.
  4. Quantum optics and teleportation
    1. Quantum teleportation: The goal of our research is to achieve more than 0.58 fidelity which is the current limit of accuracy in quauntum teleportation. A 430nm high intensity light source is being constructed for application in an optical parametric ocsillator which generates squeezed entangled states of the light field.
  5. Quantum photobiology
    1. Bacteriorhodopsin: Femtosecond dynamics of bacteriorhodopsin was investigated by sub-5-fs optical pulses. The photoexication bond alternation was clearly observed with 5-fs time resolution.