Plasmonic nanograting consisting of thermally-driven Au/SiO2 bimorph beams is developed that modulate birefringence for at the visible wavelength. From electromagnetic field simulation, the phase difference at 650 nm is calculated to be modulated from 68.5 to 23.5 degree by actuating bimorph beams. The phase difference of fabricated modulator was measured at the wavelength range of from 500 to 800 nm with a driving voltage of 10 V. Phase modulation is obtained, and the maximum variation is -3.3 degree at 646 nm. The maximum drive current is 100 mA.
We proposed and developed high aspect gold metasurface in order to improve the transmittance of plasmonic
micro half-waveplate. Expected transmittance reaches 60% from the FDTD calculation. The metasurface is
fabricated through electron beam litography (EBL) and lift-off process. Fabricated retarder was evaluated
using polarization microscopy. Achieved retardation and transmittans were 144 degrees and from 25 to 40%,
respectively. Four metasurface half-waveplates were arranged and applied to an ultrasmal radial polarization
We propose and demonstrate a novel visual encryption device composed of higher-order birefringent elements. When an
optical material with higher-order birefringence is placed between a pair of polarizers and illuminated by white light, it
appears only white. In contrast, when it is illuminated by monochromatic light, the transmitted intensity varies depending
cosinusoidally on the wavelength. An array of such materials can express information (e.g., letters and/or images) by
controlling the birefringence of each pixel. If birefringence phase retardation can be adjusted for a specific wavelength,
the information will be clearly displayed when it is illuminated at this wavelength. We denote this wavelength a key
wavelength. The encryption device was fabricated by controlling the amount of higher-order birefringence to achieve
high contrast only by using polarized illumination at the key wavelength. Thus, the information stored in the encryption
device can be decoded only by illuminating it at the key wavelength.
To demonstrate the validity of this encryption principle, we constructed a 3 × 3 pixel device in which commercial retarder
films were laminated. The device was illuminated by a monochromatic light. When a readout experiment was performed
using the monochromatic light at the key wavelength, the stored letter was clearly visible. On the other hand, when pixel
brightness was randomly distributed with illumination at the wavelength other than the key wavelength, the letter could
not be recognized.
Furthermore, the stored information can be easily distributed to multiple physical keys that display arbitrary images. In
this case, the birefringence phase retardation is obtained by summing the values of retardation of each pixel of the
physical keys. In the experimental device, the observed image was decoded by superimposing the two images using
different physical keys.
We proposed a novel pH measurement method based on two-photon fluorescence excitation of a dual-wavelength pHsensitive
dye combined with scanning near-field optical microscopy (SNOM) that can be used to evaluate mitochondrial
activity. Mitochondria produce ATP using a proton concentration (pH) gradient generated between both sides of their
inner membrane. Thus, pH distribution around mitochondria can change with time when mitochondria produce ATP.
This pH distribution has attracted interest because of its influence on necrotic cell death. Because ATP depletion causes
necrotic cell death, measurement of pH distribution around mitochondria is expected to lead to clarification of the
mechanism underlying necrotic cell death. However, it is very difficult to accurately measure pH around mitochondria
using conventional pH measurement methods. In this study, a dual-wavelength pH-sensitive dye was excited locally
using two-photon fluorescence excitation. In addition, collection-mode SNOM was used to avoid reabsorption by
collecting the fluorescent light directly from a florescence point. Using this method, we successfully calibrated pH and
observed temporal variations in pH after dropwise addition of acid. Moreover, mitochondrial activity was successfully
observed based on these pH changes.
To evaluate the thrust produced by photon pressure emitted from a 100 W class continuous-wave semiconductor laser, a
torsion-balance precise thrust stand is designed and tested. Photon emission propulsion using semiconductor light
sources attract interests as a possible candidate for deep-space propellant-less propulsion and attitude control system.
However, the thrust produced by photon emission as large as several ten nanonewtons requires precise thrust stand. A
resonant method is adopted to enhance the sensitivity of the biflier torsional-spring thrust stand. The torsional spring
constant and the resonant of the stand is 1.245 × 10<sup>-3</sup> Nm/rad and 0.118 Hz, respectively. The experimental results
showed good agreement with the theoretical estimation. The thrust efficiency for photon propulsion was also defined. A
maximum thrust of 499 nN was produced by the laser with 208 W input power (75 W of optical output) corresponding to
a thrust efficiency of 36.7%. The minimum detectable thrust of the stand was estimated to be 2.62 nN under oscillation at
a frequency close to resonance.
In this research, an electron emission method which combines field emission and plasmon resonance is proposed and
examined. Electron field emission properties of a sharp gold tip under continuous-wave laser irradiation at the plasmonresonant
wavelength are investigated. Due to the application of plasmon resonance, the electric field in the vicinity of the
emitter is strongly enhanced, resulting in the decrease of emission threshold voltage and the increase of emission current.
The emission-area is strongly confined under illumination when the optical electric field is parallel to the emitter shank,
and the optical modulation of the emission current is demonstrated.
This paper reports design, fabrication and evaluation of a novel scanning near-field probe for terahertz (THz) local
time domain spectroscopy (THz-TDS). A microfabricated scanning near-field optical microscopy (SNOM) probe was
assembled with a low-temperature-grown gallium arsenide (LT-GaAs) photoconductive antenna. The probe structure was
evaluated and determined by a finite-difference time-domain (FDTD) numerical simulation. The assembly was used as
the THz emitter and local THz source. Another LT-GaAs antenna situated at the opposite side was used as the detector. A
THz-TDS measurement using the microfabricated SNOM probe and photoconductive antenna was performed.
In this paper, we report on the design and fabrication of zinc oxide (ZnO) photoconductive antenna for a terahertz
(THz) pulse emitter and detector, and its integration with scanning near-field optical microscopy probe. The fabricated
ZnO photoconductive antennas are evaluated in a THz time-domain spectroscopy measurement system. The resistivity of
ZnO deposited by rf sputter at the room temperature was 9.6..104 ·cm. The bandwidth of ZnO photoconductive antenna
was up to 1 THz.c
The size of a particle smaller than the diffraction limit is measured using a conventional optical microscope by
adopting a standing wave evanescent field illumination. The scattering intensity from a nanoparticle is periodically
modulated by shifting the intensity fringes of standing evanescent field. By measuring the intensity variation of scattered
light during one cycle of modulation, particle sizes can be easily estimated. Furthermore, this technique has weak
dependence on the material of particles. From the experimental result, the particle size ranging from 20 to 250 nm is
successfully determined. This technique offers a low-cost size measurement for nanoparticles.