Nanometer sized particles can show size dependent physical and chemical properties. Hence,
preparation of size-controlled metal nanoparticles in a solution is one of the important subjects in
chemistry and physics of nano-scale materials. A considerable number of efforts have been directed for
developing methods of their preparation such as chemical reduction of a metal salt in a micelle or a
reversed micelle. On the analogy of the laser ablation for preparing gas-phase clusters, a laser ablation
method for preparation of metal nanoparticles in a liquid has also been developed by many researchers.
Recent development of laser ablation in a solution for the nanoparticle production is overviewed.
Mechanism of nanoparticles formation, size-reduction and relevant physical processes are described.
We developed a new fabrication technique for submicrometer spherical particles by pulsed laser melting
in liquid. In this technique, nanosecond pulsed laser irradiation at relatively low fl uence to nanoparticles
dispersed in liquid induces particle melting to form droplets, resulting in spherical particle formation by
quenching. This process produces submicrometer spherical particles of various materials, such as
metals, oxides, and semiconductors. We demonstrated a few examples of spherical particle fabrication
by this method and discussed the formation mechanism through the simple particle heating/melting
mechanism, which is basically different from the mechanism in the conventional pulsed laser ablation in
Mass production at low cost is the biggest challenge that one faces in preparation of metallic
nanoparticles by the laser ablation method in liquid. The use of ketone-suspended thin metal fl akes or
fi ne metal oxide powders as the material allowed to interact with intense nanosecond laser pulses is one
promising solution for maximizing the productivity of metal nanoparticles. This paper introduces how
the system brings about the highest-ever productivity for laser synthesis of e.g., Cu nanoparticles at the
rates ranging from 1.5 to 10 mg W‒1min‒1. This is still far from what is needed for industrial applications
of metal nanoparticles such as conductive pattern making with a highly concentrated nanoparticle
solution, and this paper also addresses how one may possibly fi ll this technical gap.
A novel method for tailoring organic nanoparticle colloids is described. Laser ablation of organic
microcrystalline powders in a poor solvent has opened new horizons for the synthesis of nanoparticles
because the powder sample is converted directly into a stable colloidal solution without additives and
chemicals. By tuning the laser wavelength, the pulse width, and the laser fl uence, we can control the
size and phase of the nanoparticles. We demonstrate examples of nanoparticle colloid preparation for
various organic compounds and describe their characteristics. We discuss the formation mechanism in
terms of the laser-induced fragmentation of organic solids and consider the potential application of
aqueous organic nanocolloids free from any additives and chemicals.
The optical emission spectroscopy of the plume formed by liquid-phase laser ablation and its application
to underwater in-situ elemental analysis (underwater laser-induced breakdown spectroscopy, underwater
LIBS) are reviewed. Since the spectral deformation due to high density in the plume is a major problem,
we overviewed the characterization of the plume, its formation mechanism, and the effects of a
cavitation bubble. Based on the plume’s properties, we discuss a laser irradiation scheme, such as the
double-pulse or long-pulse irradiation, to improve the emission spectra. Finally some applications of
underwater emission spectroscopy as an in-situ elemental analysis are described.
We reviewed a one-step method to fabricate a microstructure on a silica glass plate using laser-induced
backside wet etching (LIBWE), which is one media-assisted laser processing method based on liquid
laser ablation with a conventional pulsed laser at UV or visible wavelength. Well-defined deep
microtrenches without cracks and chipping formations on the glass plate were fabricated by LIBWE.
The system allows us to use rapid prototyping of high precision surface microfabrication of the glass and
other transparent materials as laser direct-write processing in conventional atmospheric environments.
An effi cient method to prepare surface-assisted laser desorption ionization (SALDI) substrates which are
used for mass spectrometry of biomolecules has been developed. Gold nanoparticles used as the matrix
of SALDI substrate are prepared by laser ablation in liquids. To deposit the colloidal nanoparticles,
electrophoresis, instead of dropping the colloidal solution onto a substrate reported in the previous study,
is used, because the colloidal nanoparticles prepared by laser ablation in liquids are electronically
charged. It is demonstrated that the thickness and the surface morphology of SALDI substrates are
conveniently controlled by adjusting the concentration of colloids. The SALDI effi ciency for substrates
prepared from colloids with higher concentrations was higher. The infl uence of the thickness and the
surface morphology on the SALDI effi ciency was discussed.
A colloidal solution of InP nanoparticles was prepared by laser ablation in liquid. An InP target was
irradiated in DI water, ethanol, and hexane with a Nd:YAG laser (1064 nm, 8 ns, 10 Hz). Indium metal
nanoparticles were formed as a by-product during the preparation of InP nanoparticles by laser ablation
in liquid. The primary particle size did not depend on the solvent or the energy density of laser.
Nanoparticles were well-dispersed in ethanol by electrostatic repulsion, and they aggregated in DI water
and hexane. The zeta potential of the nanoparticles in ethanol was ‒ 76 mV. Phosphoric acid was
detected in the solvent when the DI water was used as a solvent for laser ablation in liquid. The InP
target was decomposed into indium and phosphorus, and phosphorus reacted with the solvent.
Pulsed laser-induced morphological transformation and size-reduction of colloidal gold nanoparticles in
the aqueous phase were investigated using transient absorption spectroscopy and transmission electron
microscopy (TEM). Femtosecond laser-induced fragmentation of gold nanoparticles within 100 ps after
the laser pulse is interpreted in terms of the Coulomb explosion mechanism. On the other hand,
nanosecond laser-induced size-reduction of gold nanoparticles is in good agreement with the
photothermal evaporation mechanism that is based on heating of particles to temperatures above the
boiling point of gold (3100 K). Here, the experimentally observed fragmentation thresholds were wellreproduced
by simulations based on electron and lattice temperature models and by considering the
dissipation of heat into the surrounding medium. The numerical method described herein has the
advantage of identifying the fragmentation mechanism by considering pulse duration- and energydependent
thresholds. To-date there is no other convenient measures to distinguish between the
photothermal evaporation and the Coulomb explosion mechanisms.
We report on investigations of silicon nanocrystals (Si-ncs) surface engineering and subsequent
integrations into sub-micrometer structures induced by nanosecond laser processing in water. We
present that easy and low-cost methods through nanosecond laser processing in water allow of Si-ncs
integration self-assemblies ranging several micrometers and sub-micron spherical particles. Room
temperature photoluminescent properties were preserved in these particles.
We investigated a new fabrication technique for spherical particles by pulsed laser melting in liquid. In
this technique, nanoparticles dispersed in liquid were melted by nanosecond pulsed laser irradiation with
adequate fl uences, and the formed droplets became spherical particles after cooling. We investigated the
infl uences of laser wavelength, fl uence, and dispersion medium on the obtained particles by irradiating
the laser on titanium dioxide nanoparticles dispersed in ethanol and deionized water. We confirmed
nanometer-sized sphere formation with submicrometer spheres by laser irradiation at relatively high
laser fl uence.
This paper reports the beam wave fl uctuations caused by strong atmospheric turbulence. These beam
wave fl uctuations are estimated by numerical calculations carried out using moment equation analysis
with thin phase screen approximation. The scintillation index for a plane wave is calculated as a
function of a parameter concerning the intensity of atmospheric turbulence, and the result is in good
agreement with previous studies. Transmission of the beam radius dependence of a scintillation index is
calculated using the first and second moments of wave intensity. The largest scintillation index is
obtained when the beam radius size equals (λ z/2π )1/2. The scintillation index of a beam wave is also
evaluated using the Rytov approximation method, which is based on perturbation analysis.
We demonstrate a compact, high-spatiotemporal-quality, high-intensity diode-pumped Yb:YAG thin-disk
chirped-pulse amplification (CPA) laser system that incorporates a nonlinear preamplifier based on
optical parametric chirped-pulse amplification (OPCPA). The stretched pulses are amplified in the
OPCPA preamplifier and the following Yb:YAG main amplifier to ～100 mJ at 10 Hz. The broadband
amplified beam quality of 1.1 (horizontal direction) and 1.4 (vertical direction) times diffraction limited
and pulse compression down to 470 fs with contrast of better than 10－8 have been achieved successfully.