Fluorescence from cells excited by deep-ultraviolet (DUV) light is known as autofluorescence and intrinsic properties of cells. Therefore, the imaging of the distribution of autofluorescence of biological specimen enables us to promote tissue histology and cell biology. This fluorescence is, however, very weak, which prevents the development of autofluorescence imaging. The present work utilizes the surface plasmon resonance (SPR) on aluminum surfaces to enhance the fluorescence signals for highly sensitive imaging of living cells without staining. Aluminum is promising material for the excitation of SPR in the DUV region (DUV-SPR) due to their negative permittivity. DUV-SPR was excited with Kretschmann configuration using a sapphire prism. The DUV-SPR excitation of Al thin film through a sapphire prism was investigated theoretically and experimentally. For living biological specimen, i.e. water-immersed specimens, a high refractive index of the sapphire is suitable for the observation. The autofluorescence intensity through DUV-SPR is increased ~3-fold. Results from this work provide an effective technique for highly sensitive label-free observation of living biological specimens.
We have developed a stimulation method for a living cell by using electron beam exposure. Liquid water is a major
chemical component of a cell and is expected to be decomposed into reactive oxygen species (ROS) upon the beam
exposure, which is known as a cellular signaling molecule and modulates various cellular functions. The beam target cell
is stained with a fluorescence probe, CM-H2DCFDA which is sensitive to intracellular ROS and emits bright fluorescence
once it reacts with ROS. By comparing the fluorescence intensity of the target cell before and after the beam exposure, it
is implied that intracellular ROS is generated by electron beam irradiation. Therefore, this method can modulate cellular
physiology through artificial generation of ROS, which is applied for future biological researches.
We proposed an addressable potentiometric sensor for ion imaging using a focused electron beam instead of the light. The electron beam can be easily focused to a spot of several nanometer, and it enable to improve the spatial resolution. The electron beam for imaging the ion concentration distribution is scattered in a sensor substrate and the spatial resolution is reduced. Therefore, it is necessary to reduce the scattering in order to realize a high spatial resolution. In order to reduce scattering, the acceleration voltage of the electron beam and the film thickness of the sensor substrate were examined.
Second harmonic generation (SHG) behaviors will be presented for NLO polymer/Au nanoparticle hybrid structures. The NLO polymer is the material rich in the nonlinear susceptibilities and it is suitable for coating on the metal surfaces. The Au nanoparticles themselves exhibit enhanced SHG effects at localized surface plasmon (LSP) resonances. Our experimental results demonstrated that the Au nanoparticles coated with the NLO polymer emitted more than one magnitude higher SHG signals than the bare Au nanoparticles. The enhanced nonlinearities due to the NLO polymers were explained in terms of not only electromagnetic mechanism but also molecule-to-metal charge transfer mechanism.
We present second harmonic generations (SHG) of NLO polymers grown on Ag thin films at surface plasmon polariton (SPP) resonances. The Ag film itself exhibits surface nonlinear susceptibility and it is enhanced at the SP resonances. Our experimental results demonstrated that growing the NLO polymer layers on the Ag films was useful for further amplifying the conversion efficiencies of the SP-enhanced SHG. There was optimal polymer thickness for the SHG conversions, and approximately 40-fold maximum amplification was gained. The dependency of the SHG conversions on the polymer thickness was explained in terms of the bulk nonlinearities and the multiple reflections inside the polymer layer.
We have developed an electron beam addressable potentiometric sensor to improve the spatial resolution. Ion sensors are widely used in the fields of medical and life science, food and material development, environmental protection and so on. However, the spatial resolution of the ion distribution imaging sensor is limited by the diffraction limit of light or microfabrication technology. So, we proposed an addressable potentiometric sensor using a focused electron beam instead of light. The electron beam can be easily focused to a spot of several nanometer, and the spatial resolution of the addressable potentiometric sensor improved. We showed that ion concentration can be measured by irradiating the ion sensor substrate (SiN/SiO2/Si) with a focused electron beam.
The paper presents second harmonic generations (SHG) from Au nanoprisms at localized surface plasmon resonances.
The model system was equilateral triangular nanoprisms that were arranged two-dimensionally in trigonal lattices. At
lower excitation power regions, the SHG conversion efficiencies were almost independent of the excitation light
polarization angles, while the polarization angles of the SHG waves were twice as much as those of the excitation light
polarizations. The polarization dependencies were in a good agreement with the demands required from the C3v point
symmetry of the systems. On the other hand, the SHG conversion efficiencies were dependent on the excitation light
polarization angles at higher excitation power regions. The anisotropy in the nonlinear optical responses was explained
from the viewpoint of the polarization-dependent depletions of the surface electrons on the metal surfaces.
We demonstrated that the high spatial resolution absorption contrast imaging of the crystal of vitamin B9 having absorption at UV wavelengths. The absorption wavelength matches with the wavelength of the emission of the fluorescent thin film of an electron-beam excitation assisted (EXA) optical microscope. The fine crystal structure was imaged beyond the optical diffraction limit. The image contrast corresponded with the thickness of the crystal. The illumination light is absorbed with the vitamin B9 crystal and the intensity of the transmitted light depends on the thickness of the vitamin B9 crystal. The EXA optical microscope is useful for analysis of growth of a crystal, bioimaging, and so on.
We present high spatial-resolution label-free imaging with an electron-beam excitation-assisted optical microscope (EXA microscope). The EXA microscope improves the spatial resolution down to 100 nm. To realize the high spatial resolution, a nanoscale optical spot is generated by irradiating a fluorescent thin film with a focused electron beam whose spot size is less than 10 nm. The size of the optical spot becomes smaller than the diffraction limited spot size and is reduced to about 100 nm, because the light emission is localized in nanometer-sized region. In this microscopy, it is not necessary to label a specimen for imaging beyond the diffraction limit of the light. The specimen stage is separated from the vacuum chamber of the scanning electron microscope by the fluorescent thin film and a specimen under atmospheric pressure can be imaged.
We demonstrated that the high spatial resolution absorption contrast imaging of the crystal of vitamin B9 having absorption at UV wavelengths. The absorption wavelength matches with the wavelength of the emission of the fluorescent thin film we deposited. The fine crystal structure was imaged beyond the optical diffraction limit. The image contrast corresponded with the thickness of the crystal measured with an atomic force microscope (AFM). The illumination light is absorbed with the vitamin B9 crystal and the intensity of the transmitted light depends on the thickness of the vitamin B9 crystal. The EXA microscope is useful for analysis of growth of a crystal, bio-imaging, and so on.
We investigated the surface plasmon resonance (SPR) of aluminum (Al) thin films with varying refractive index of the environment near the films in the far‒ultraviolet (FUV, ≤ 200 nm) and deep‒ultraviolet (DUV, ≤ 300 nm) regions. By using our original FUV‒DUV spectrometer which adopts an attenuated total reflectance (ATR) system, the measurable wavelength range was down to the 180 nm, and the environment near the Al surface could be controlled. In addition, this spectrometer was equipped with a variable incident angle apparatus, which enabled us to measure the FUV‒DUV reflectance spectra (170–450 nm) with various incident angles ranging from 45° to 85°. Based on the obtained spectra, the dispersion relation of Al‒SPR in the FUV and DUV regions was obtained. In the presence of various liquids (HFIP, water, alcohols etc.) on the Al film, the angle and wavelength of the SPR became larger and longer, respectively, compared with those in the air (i.e., with no materials on the film). These shifts correspond well with the results of simulations performed according to the Fresnel equations, and can be used in the application of SPR sensors. FUV‒DUV‒SPR sensors (in particular, FUV‒SPR sensors) with tunable incident light wavelength have three experimental advantages compared with conventional visible‒SPR sensors, as discussed based on the Fresnel equations, i.e., higher sensitivity, more narrowly limited surface measurement, and better material selectivity.
In this research, we demonstrate the enhanced autofluorescence and high-sensitivity bioimaging of intracellular organelles using DUV-SPR. The Kretschmann configuration is used for excitation of DUV-SPR. We used an aluminum thickness of 24 nm. The alumina surface was estimated to be 6 nm by comparison between the experimental and calculated results. Reflectance after culturing of cells was measured. DUV-SPR is excited at an incident angle of 52° after the biological samples are cultured.
MC3T3-E1 cells as Label-free cells are directly cultured on an aluminum and glass surfaces, and they were cultured on the both substrates in an incubator. Autofluorescence spectra excited of the label-free MC3T3-E1 cells was measured by 266-nm exictation. The autofluorescence intensity for the aluminum is higher than that for the glass. In the autofluorescence spectra, MC3T3-E1 cells exhibited two fluorescence peaks, which were located around 330 and 500 nm. These 330 and 500 nm emissions indicate aromatic amino acid and mitochondria, respectively. Both of the ehnahcement factors were 8 times.
We also observed autofluorescence of aromatic amino acid and mitochondrial NADH in the label-free MC3T3-E1 cells cultured on the aluminum and glass surfaces. In the autofluorescence image with DUV-SPR, organelles can be clearly observed in the MC3T3-E1 cells. On the other hand, the autofluorescence intensity is very weak in the image without DUV-SPR.
Accordingly, DUV-SPR can facilitate the observation of proteins, DNA in nucleus, and other structures that cannot be excited by visible light. DUV-SPR is shown to be a powerful technique for acquiring high-sensitivity label-free observation of biological samples.
We present second-order nonlinear optical properties of two-dimensional periodic arrays of Au nanorods arranged two dimensionally on SiO2 along with the one-dimensional periodic arrays in the direction either coaxial or vertical to the plasmon polarizations. The geometry of the nanorods was symmetric with respect to the normal line to the top surface of the rods, and the system was excited at oblique incidence angles so as to break the centro-symmetry. Our experimental results demonstrated that the coordination longitudinal to plasmon polarizations reduced the nonlinearities of the nanorods while the coordination transverse to polarizations did not give any significant influences on them.
The second harmonic generations (SHG) from Au nanorods coated with the nonlinear optical (NLO) polymers will be presented. The thin films of the NLO polymers with the different transition frequencies were prepared. The SHG conversion efficiencies were highly enhanced by coating the NLO polymers on the nanorods. The conversion efficiencies were higher, as the transition wavelengths of the NLO polymers were closer either to the pump light wavelength or its second harmonic wavelength. About five-fold enhancement in the conversion efficiency was recorded from the nanorods of which absorption peak was almost exactly resonant to the second harmonic wavelength, comparing with that from the pristine PMMA coated nanorods.
The presentation will report nonelectrical poling behaviors of guest-host polymers, consisting of Disperse Red1 (DR1)
and poly (methyl methacrylate) and related second-order nonlinear optical susceptibilities. Our present experimental
results found the emissions of the second harmonic generations from the polymer thin films on SiO2 glass substrates after annealing the materials at the temperatures higher than the glass transition temperatures of the PMMA even in the absence of applying the external electric fields. The hydrogen bonds between the hydroxyl groups of the DR1 and the
silanols of the substrate surely played essential roles for breaking the centrosymmetry in the alignments of the guests.
The optimized conditions of the nonelectrical poling procedures were examined from the standpoints of the polymer film
thickness and the concentrations of the guest chromophores.
We will report second harmonics generations (SHG) in nonlinear optical (NLO) polymers excited by Surface Plasmon
(SP) enhanced fields. The surface plasmon polariton was excited in an attenuated total reflection geometry having the
Kretchmann configuration. Here, the NLO interactions occurred in the thin films of the NLO polymers, consisting of
Disperse Red 1 as guest chromophores and PMMA as host, coated on Ag thin films. Our experimental results indicated
that NLO polymers emitted strong SHG signals in the SP resonance conditions. The SHG intensities from NLO polymer
coated Ag films were more than 10 times higher than those of the uncoated Ag films. The measurements were conducted
for the polymer films with different thickness between 10 and 100 nm. All of the samples with different polymer
thickness exhibited the SHG signals at its SP resonance condition that depends on the film thicknesses. The highest SHG
conversion efficiency was recorded from the sample with 40 nm film thicknesses. The p-polarized pump beams gave the
highest SHG conversion efficiency while the s-polarized ones gave almost no signals. On the other hand, the
polarizations of the SH signals were highly oriented in the direction of the p-polarizations. The SP-enhanced field
attracts a lot of interests as light sources for sub-diffraction-limit imaging. The SP can be excited only in the regions
lower than surface plasma frequencies peculiar to the metals. The present frequency conversion technologies for the SP
enhanced fields in the NLO polymers will extend the frequency regions available for the sub-diffraction-limit imaging.
Here, we will propose poly (cyano phenylene sulfide) as novel host materials of nonlinear optical (NLO) polymers. Our
experimental results proved that NLO chromophore-doped PCPS thin films deposited on the metal layers exhibited
second order NLO susceptibilities just by annealing at the temperatures higher than a glass transition point even without
conventional poling procedures. We determined the optimized annealing temperatures and the film thickness for the
nonelectrical poling procedure. The nonelectrical poling procedure was applicable for the films as thick as a few μm.
The second order nonlinear coefficient of was 0.5 pm/V for the PCPS doped with 10w% of 4-[Ethyl(2-
hydroxyethyl)amino]-4'-nitroazobenzene. Taking advantage of the unique polarization self-organization procedure, we
may prepare one- or two-dimensionally periodically poled structures in these materials for the second-order NLO active
photonic crystals pretty easily.
We designed and proposed a focusing device for the localization of photons in nanometric region by surface plasmon
excitation. The focusing device is a metal-coated axicon prism. The cone angle of the prism and the metallic film
thickness are designed to match the excitation conditions for Kretschmann configuration. A collimated Gaussian beam is
irradiated to the prism and the excited surface plasmons propagate along the sides of the prism and converge at its apex.
The resulting nanofocusing was investigated by the simulations and experiments of the intensity distributions around the
apex of the prism. For incident radial polarization, a localized and field enhanced spot is generated by the constructive
interference of surface plasmons. We observed the light scattered at the apex and the light reflected by the prism. Each
polarized light of the radial, azimuthal, and linear provided field distributions of bright and dark intensities according to
the surface plasmon excitation. We have demonstrated that surface plasmon waves are excited at the sides of the prism in
the Kretschmann configuration and that they converge to its apex.
We developed a compact and high-power mode-locked fiber laser for three-dimensional optical memory. Fiber
lasers have the potential to be compact and stable light sources that can replace bulk solid-state lasers. To
generate high-power pulses, we used stretched-pulse mode locking. The average power and pulse width of the
output pulse from the fiber laser that we developed were 109 mW and 2.1 ps, respectively. The dispersion of the
output pulse was compensated with an external single-mode fiber of 2.5 m length. The pulse was compressed
from 2.1 ps to 93 fs by dispersion compensation. The pulse emitted from this fiber laser has a sufficient energy to
generate two-photon recording effectively, so the fiber laser we have developed is possible to use as a light source
of three-dimensional optical memory. We also propose an all-fiber recording and readout system for multilayered
memories.
Simultaneous observation of quenched wide-gap semiconductor crystals has been observed using single- and two-photon
luminescence. It is was found at the quenched area, single-photon excitation gives luminescence read-out compared to
two-photon which no luminescence detected at the bandgap wavelength. This is due to transition of electron between the
bandgap in the two-photon luminescence to occur have been demolished by the quenching which involved two-photon
quenching process. Furthermore, side lobes that exist in the longer part of the luminescence spectrum are resulted by
decreasing in the Stark effect which increased the transition energy. The dependency if excitation power with the
observed from the crystal's luminescence is elaborated which confirmed the single- and two-photon luminescence
methods.
We proposed a concept of a roll-type optical advanced memory (RoCAM). RoCAM is a multilayered optical
memory, in which recording layers are wound onto a shaft. Multilayered media are fabricated easily by winding
a two-layered filmlm, which is composed of a photosensitive layer and a pressure-sensitive adhesive (PSA) layer.
We showed certain advantages of RoCAM and also demonstrated a prototype of RoCAM and the recording and
reading results for two layers.
We report a systematic investigation on the imaging behavior of an optical system consisting of a lens made of a uniaxial birefringent crystal sandwiched between two linear polarizers with the introduction of prespecified off-axis aberrations such as astigmatism and coma. The intensity point spread function is used as the image assessment parameter. It has been shown that for a point object, the proposed system has higher tolerance to the presence of off-axis aberrations than an imaging system formed by an ordinary glass lens. Some specific cases are computed and illustrated graphically.
We have fabricated a new optical storage media using minute spheres arranged on surface relief grating (SRG). By using minute spheres as recording bits, we can limit recordable regions by sphere size, since one mintue sphere becomes one recording bit. We can realize high resolutive reconstruction in the plane direction. We make surface relief structures on a polymer thin fim, and tried to perform diffusion arrangement and adsorptive fixation of minute spheres on it. The stability of arranged spheres was confirmed for heating and washing. Furthermore, we tried dipping method for more simple arranging minute spheres on a large area of the substrate and have made a monolayer sample of the spheres. We are able to realize high sensitive reconstruction of the media using the confocal optical system as record and readout systems. We have also succeeded in doping the recordable dyes in minute spheres.
Three-dimensional optical memory with photorefractive materials is discussed for ultra-high density/capacity memory exceeding the classical limit of a conventional optical recording system. Bit data are recorded as highly localized refractive index variations in three-dimensional volume using a focused laser beam. We show recording and reading results using various recording materials and optical configurations. A multi-structured optical recording medium
using a photoisomerization polymer and a transparent films has
been developed for reflection confocal reading. Two-photon recording is also demonstrated.
3D optical memory with photorefractive materials is discussed for ultra-high density/capacity memory exceeding the classical limit of a conventional optical recording system. Bit data are recorded as highly localized refractive index variations in 3D volume using a focused laser beam. We show recording and reading results using various recording materials and optical configurations. A multi-structured optical recording medium using a photoisomerization polymer and a transparent films has been developed for reflection confocal reading. Two-photon recording is also demonstrated.
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