Recently, we discovered, for the first time, reverse saturable scattering in a single gold nanoparticle. When incident intensity increases, the scattering intensity dependence of 80-nm gold nanoparticles evolves from linear, to saturation, and to reverse saturation sequentially. The intensity dependence in reverse saturable scattering region is significantly steeper than that in the linear region. With the aid of a confocal microscope, the full width half maximum of the single-particle point spread function can be reduced down to 80 nm, which is beyond the diffraction limit. Our finding shows great potential for superresolution imaging application without bleaching.
The wavelength and size dependencies of nonlinear scattering by a single gold nanosphere immersed in oil are presented. We show that the wavelength dependency fits well with the scattering spectrum by Mie solution, reflecting that the nonlinear scattering is dominated by the field enhancement from plasmonic effects. The tendency for different sizes is consistent with the results of degenerate four-wave mixing in the literature, showing that the saturation behavior is governed by the Kerr nonlinearity resonantly enhanced via intraband transition. Thus we conclude that the saturable scattering in our case is attributed to intraband χ(3), with nonlinear behavior enhanced by LSPR.
Two photon polymerization (TPP) lithography has been established as a powerful tool to develop 3D fine structures of polymer materials, opening up a wide range applications such as micro-electromechanical systems (MEMS). TPP lithography is also promising for 3D micro fabrication of nanocomposites embedded with nanomaterials such as metal nanoparticles. Here, we make use of TPP lithography to fabricate 3D micro structural single wall carbon nanotube (SWCNT)/polymer composites. SWCNTs exhibit remarkable mechanical, electrical, thermal and optical properties, which leads to enhance performances of polymers by loading SWCNTs. SWCNTs were uniformly dispersed in an acrylate UV-curable monomer including a few amounts of photo-initiator and photo-sensitizer. A femtosecond pulsed laser emitting at 780 nm was focused onto the resin, resulting in the photo-polymerization of a nanometric volume of the resin through TPP. By scanning the focus spot three dimensionally, arbitrary 3D structures were created. The spatial resolution of the fabrication was sub-micrometer, and SWCNTs were embedded in the sub-micro sized structures. The fabrication technique enables one to fabricate 3D micro structural SWCNT/polymer composites into desired shapes, and thus the technique should open up the further applications of SWCNT/polymer composites such as micro sized photomechanical actuators.
We present a fabrication method of gold nanorod/ polymer composite microstructures by means of a femtosecond
near-infrared laser light. The mechanism of this method is based on a cooperation of two optical reactions;
two-photon polymerization (TPP) reaction only at the surface of gold nanorods, and optical accumulation of gold
nanorods in photo-polymerizable resin. Gold nanorods were mass-produced by seed mediated growth method, and
were mono-dispersed in photo-resin. The wavelength of the laser light was tuned resonant to two-photon
absorption of the photo-resin, and also close to a longitudinal local surface plasmon resonance (LSPR) mode of the
gold nanorods. The laser light excited LSPR onto gold nanorods, resulting in the formation of thin polymer layer
only at their surface through TPP. Concurrently occurring optical accumulation of gold nanorods by continuous
irradiation of laser light, gold nanorods got together into focus spot. The TPP layer at the surface of gold nanorods
worked as a glue to stick one another for forming their aggregated structure in micro/nano scale. By controlling
the intensity and the exposure time of laser light, an optimal condition was found to induce dominant polymerization
without any thermal damages. The scanning of the focus spot makes it possible to create arbitrary micro/nano
structures. This method has a potential to create plasmonic optical materials by controlling the alignment of gold
We present femtosecond laser induced photobleaching of individually isolated single-wall carbon nanotubes.
Monodispersed single-wall carbon nanotubes fixed in aqueous gel were exposed under tightly focused femtosecond
laser light. We measured photoluminescence spectra of single-wall carbon nanotubes before/after the laser irradiation.
Because of unique excitonic band structures of single-wall carbon nanotubes, we clearly observed strong selectivity in
the chirality and the orientation of carbon nanotubes depending on the wavelength and polarization of laser light. We
also observed the difference from the case of continuous wave laser irradiation in the chirality selectivity and the
efficiency of photobleaching.
We present evidence that, when laser light was tightly focused into aqueous suspension of
mono-dispersed single-wall carbon nanotubes (SWCNTs), density of nanotubes was locally
increased at the focus spot of light. We prepared mono-dispersed HiPco SWCNTs in an aqueous
surfactant solution by sonication and following ultracentrifugation. We built a confocal Raman
microscope system equipped with a 633 nm He-Ne laser, and launched the laser light into SWCNTs
suspension filled in a glass micro-cell by a high numerical aperture objective lens (N.A.=1.35).
We monitored temporal change in Raman spectrum of SWCNTs excited by the laser light. We
clearly observed significant intensity increase of a particular radial breathing mode, however the
increase of the Raman signal did not last permanently, rather showed transient response. This
result implies that SWCNTs with particular chirality were selectively accumulated by optical
gradient force of Raman-probing laser light. We discuss the independent behavior of the radial
breathing modes, with respect to the wavelength of the laser light and the chirality of corresponding
We report optical polarizer made of single-wall carbon nanotubes/poly(vinyl alcohol) composite. The film of the
composite was mechanically stretched to form uniaxial alignment of carbon nanotubes in the polymer matrix. In order to
obtain well-aligned carbon nanotubes efficiently, we used single-wall carbon nanotubes shortened into the length of less
than 200 nm. Thanks to π plasmon-originated broad absorption spectrum and strong anisotropy of single-wall carbon
nanotubes, the film exhibits the degree of polarization of ~ 95 % with keeping flat transmittance through spectral region
from 350 nm to 800 nm. We also observed enhancement of the degree of polarization at the wavelengths of van Hove
We present a method for fabricating 3D photonic crystal structures by means of interference pattern of laser beams. Four laser beams are introduced into a glass cell filled with a liquid photopolymerizable resin. The resin is polymerized according to the interference patter of four laser beams formed in the resin, so that a square lattice of solid polymer rod-array is formed. Four beams are introduced into the cell again from another face, which is perpendicular to the previous entrance face, to form another rod-array inside the previous one, thereby producing a 3D photonic crysatl structure. The shape of the formed lattice is so-called "wood-pile" which has diamond-like lattice symmetry. The lattice constant of the photonic crystal can be tuned by selecting incident angles of laser beams and can be minimized to about a half of the laser wavelength. After irradiation of laser light, the non-solidified resin is washed out of the polymer structure by ethanol. The proposed method does not require complicated multiple processes compared with the layer-by-layer fabrication method, and thick photonic crystals are immediately produced with high precision.
3D photonic crystal structures can be fabricated into photopolymerizable resins by using laser beams interference with high precision. Three laser beams interfere into a glass cell filled with a liquid photopolymerizable resin to form a hexagonal periodic structure. Rods are formed in hexagonal arrangement after being photopolymerzed according to the 3D periodic light distribution which resulted from the lasers interference. Two beams of another laser interfere also to form layers which cross perpendicularly the rods array. After photo-fabrication, the non-solidified resin is removed by ethanol. The lattice constant can be selected by tuning the angles of the incident beams and the laser wavelength. We have fabricated a 500 m X 500 m X 500 m photonic crystal structure, the lattice constant of which is 1 m, and which contains 150 lateral layers.
We present evidence of optically-induced growth of fiber patterns into a photopolymerizable resin. Optical growth of a single or multiple fibers is achieved by focusing a laser light into the photopolymerizable resin used. The fiber growth is due to an effect in which photopolymerization of the resin upon light irradiation produces an increase of the resin refractive index, the change of which, in turn, confines the light propagation into waveguide-type fiber structures. We have also observed that two optically grown independent fibers can merge to form a single fiber under specific conditions. We have studied the dependence of this optical growth of fiber structures phenomena on all the experimental parameters, including the numerical aperture (N.A.) of the lens used to focus the light, the light power, and the exposure time.
We have developed a method to fabricate photonic crystals using an interference pattern of laser beams. Photopolymerizable resin is used for solidifying a lattice. Interference of two beams forms a one-dimensional grid and a two-dimensional lattice, and that of three beams forms a three-dimensional hexagonal lattice. The experimental setup and the process of fabrication are described. The use of the structure to photonic crystal is also discussed.