Refereed publications

1. H. Ishida, R. Mizoguchi, K. Onda, C. Hirose, S. S. Kano, and A. Wada, “Second harmonic observation of Cu(111) surface: in situ measurements during molecular adsorption”, Surface Science, Vol. 526, February 2003, pp. 201-207.
   Abstract - Second harmonic generation (SHG) spectroscopy using a tunable femtosecond laser has been demonstrated as an effective and a practical in situ monitor of surface electronic states during adsorption processes. We have successfully shown this technique to be suitable for the study of surface electronic states, not only those induced by adsorbed molecules but also those associated with clean surfaces. By observing the change in the SH signals from a Cu(111) surface during exposure to benzene or CO molecules, we discovered new resonances of the clean Cu surface that could not be ascribed to the well-known surface state (SS)–image state (IS) transition. One of these was from a surface site that is less likely to adsorb benzene, where the SH signal intensity was kept constant until the Cu surface was covered by the sub-monolayer.
2. H. Noguchi, T. Okada, K. Onda, S. S. Kano, A. Wada and K. Domen, “Time-resolved SFG study of formate on a Ni(111) surface under irradiation of picosecond laser pulses”, Surface Science, Vol. 528, March 2003, pp.183-188.
   Abstract - Time-resolved sum-frequency generation spectroscopy was carried out on a deuterated formate (DCOO) adsorbed on Ni(1 1 1) surface to investigate the surface reaction dynamics under instantaneous surface temperature jump induced by the irradiation by picosecond laser pulses. The irradiation of pump pulse (800 nm) caused the rapid intensity decrease of both CD and OCO stretching modes of bridged formate on Ni(1 1 1). Different temporal behaviors of intensity recovery between these two vibrational modes were observed, i.e., CD stretching mode recovered faster than OCO. This is the first result to show that the dynamics of adsorbates on metals strongly depends on the observed vibrational mode. From the results of temperature and pump fluence dependence, we concluded that the observed intensity change was not due to the decomposition or desorption, but was induced by a non-thermal process.
3. J. Kubot, A. Wada, S. S. Kano and K. Domen, “Time-resolved study of D2O ice crystal on CO/Pt(111) by ultra-short NIR laser pumping: melting and recrystallization without desorption”, Chemical Physics Letters, Vol. 377, August 2003. pp. 217-222.
   Abstract - The transient response of 10 molecular layers of D2O ice on CO/Pt(111) at 130 K was investigated under ultra-high vacuum following a near-infrared pump pulse of 35 ps by sum frequency generation (SFG) spectroscopy. The D2O molecules in the ice crystalline layer formed an amorphous or liquid-like structure in response to the pumping without desorption of D2O to the gas phase, and the crystals returned to the crystal structure on a sub-nanosecond time scale.
4. S. Katano, S. Dobashi, J. Kubota, K. Onda, A. Wada, S. S. Kano and K. Domen, “Structural change of CO adsorbed on Pt(111) by laser heating: time-resolved sum-frequency generation study”, Chemical Physics Letters, Vol. 377, August 2003. pp. 601-606.
   Abstract - The IR–visible sum-frequency generation (IVSFG) method was used to perform time-resolved vibrational measurements of CO/Pt(111). Irradiation of intense picosecond laser pulses (35 ps, 1064 nm) resulted in a drop in intensity, red shift, and broadening of the on-top CO stretching peak, followed by recovery to the original peak shape on the order of hundreds of picoseconds. The transient behavior of the CO stretching signal was found to depend on the CO coverage. The transient spectra at saturation coverage consisted of a single peak, whereas at low coverage (0.25 ML) the line shape became asymmetric and each transient peak could be deconvoluted to the multiple components. The origin of the remarkable change in the transient spectral features at the 0.25 ML surface is discussed.
5. R. Mizoguchi, S. S. Kano and A. Wada, “Optical control of excited states of α-perylene crystal using optimized pulse shaping method”, Chemical Physics Letters, Vol. 379, September 2003. pp. 319-324.
   Abstract - Optical control of excited states of α-perylene crystal was realized by a femtosecond optimized pulse shaping method using Genetic Algorithm (GA). We succeeded in controlling the emission spectral feature of an α-perylene crystal; the intensity of E-emission was increased by a factor of 1.4 without the change of Y-emission intensity. Furthermore, we found a near-infrared pulse shape whose multi-photon excitation efficiency is larger than that of a single femtosecond pulse by a factor of two. On the auto-correlation traces of these shaped pulses, the several satellite peaks appeared beside the main peak. The origin and mechanism of the attained change were discussed.
6. J. Kubota, E. Yoda, N. Ishizawa, A. Wada, K. Domen, and S. S. Kano, “Site-Hopping of Adsorbed CO in c(4×2)-CO/Ni(111) by Laser-Induced Temperature Jump: Time-Resolved Sum-Frequency Generation Observation”, Journal of Physical Chemistry B, vol.107, September 2003, pp 10329 – 10332.
   Abstract - The c(4x2)-CO/Ni(111) surface under pulsed near-infrared irradiation is examined by time-resolved sum-frequency generation (SFG) spectroscopy. At a surface coverage of 0.5, the surface is confirmed to consist almost exclusively of hollow CO molecules, as evidenced by a sole SFG peak at 1904 cm^-1. Under pulsed irradiation this peak weakened, followed by the emergence of a new peak attributable to atop CO. This represents a direct observation of site-hopping of adsorbed CO. The hopping phenomenon was found to be entirely transient, with the surface returning to the pre-excited state within a few hundred picoseconds without desorption. The dynamics of the process are also discussed.
7. R. Mizoguchi, K. Onda, S. S. Kano, and A. Wada, “Thinning-out in optimized pulse shaping method using genetic algorithm”, Review of Scientific Instruments, Vol. 74, May 2003, pp. 2670-2674.
   Abstract - An optical pulse shaping system using a spatial light modulator (SLM) controlled by genetic algorithm (GA) optimization was improved and we demonstrated that the time for finding the optimal condition could be shortened by a proposed "thinning out" method. In this method, GA controls only every N (N = 1, 2, 4, 8, 16) pixel in the SLM. The conditions of the remaining pixels are derived by interpolation. The effectiveness of this method was verified by the pulse compression of chirped femtosecond pulses and the increase in the two-photon excitation efficiency of α-perylene crystals. The influence of the thinning out on the pulse shape is discussed, and an advanced method is proposed. It is shown that the disadvantages of the thinning out method can be compensated for by changing the value of N during optimization.

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