| Refereed publications
- 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.
- 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.
- 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.
- 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 IRvisible
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.
- 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.
- 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.
- 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.
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.