Optical Review
Subwavelength-sized beam spot confinement using an optical thin core dielectric ridge-type waveguide in leaky mode
Fri, 2010-07-30 20:03 — Guest
Abstract
Optical near-field plasmon-enhancement techniques have made marked contributions to the field of subwavelength optical beam
spot generation for photonic devices. However, the metal material used is not sufficiently heat resistant for high-temperature
operating requirements, such as laser-assisted magnetic recording storage. Therefore, it is preferable to use a dielectric
material as a heat source for this application. To realize a subwavelength optical beam spot size using a dielectric material,
we extensively analyze a leaky mode dielectric waveguide with a thin core. Finally, we show a new ridge-type dielectric waveguide
using a leaky mode operation for a subwavelength beam spot.
spot generation for photonic devices. However, the metal material used is not sufficiently heat resistant for high-temperature
operating requirements, such as laser-assisted magnetic recording storage. Therefore, it is preferable to use a dielectric
material as a heat source for this application. To realize a subwavelength optical beam spot size using a dielectric material,
we extensively analyze a leaky mode dielectric waveguide with a thin core. Finally, we show a new ridge-type dielectric waveguide
using a leaky mode operation for a subwavelength beam spot.
Compact beam collimator for laser diode bar
Fri, 2010-06-04 18:49 — Guest
Abstract
A compact beam collimator for a laser diode (LD) bar fabricated by a simple method is presented. It consists of a single set
of microlenses and a cylindrical lens, which are fabricated from SiO2 rods using a fiber-drawing tower. The principle and parameter optimization of this device are investigated numerically using
ZEMAX software and illustrated experimentally for a specific LD bar. It is shown that the output beam is well collimated in
both the fast-axis and slow-axis directions; the beam quality is greatly enhanced via the redistribution of intensity in the
two directions and by eliminating the fill factor for the LD bar.
of microlenses and a cylindrical lens, which are fabricated from SiO2 rods using a fiber-drawing tower. The principle and parameter optimization of this device are investigated numerically using
ZEMAX software and illustrated experimentally for a specific LD bar. It is shown that the output beam is well collimated in
both the fast-axis and slow-axis directions; the beam quality is greatly enhanced via the redistribution of intensity in the
two directions and by eliminating the fill factor for the LD bar.
Broadly tunable UV-blue picosecond pulsed laser and its application for biological imaging
Fri, 2010-06-04 18:49 — Guest
Abstract
We have achieved a rapid and random wavelength tuned picosecond pulsed laser and a widely tunable UV-blue picosecond pulsed
laser by using the intracavity second harmonic generation of the laser. The tuning range was from 384 to 434 nm with picosecond
pulse oscillation. In addition, we demonstrated biological imaging using a fluorescent protein excited by the widely tunable
UV-blue picosecond pulsed laser. We found that the laser is suitable for biological imaging using the fluorescent protein
as an excitation light source without damages.
laser by using the intracavity second harmonic generation of the laser. The tuning range was from 384 to 434 nm with picosecond
pulse oscillation. In addition, we demonstrated biological imaging using a fluorescent protein excited by the widely tunable
UV-blue picosecond pulsed laser. We found that the laser is suitable for biological imaging using the fluorescent protein
as an excitation light source without damages.
A novel double-pulse laser plasma spectroscopic technique for H analysis in metal samples utilizing transversely excited atmospheric-pressure CO2 laser-induced metastable He atoms
Fri, 2010-06-04 18:48 — Guest
Abstract
The analysis of hydrogen in a metal sample (zircaloy-4), which is usually difficult to perform using conventional laser-induced
breakdown spectroscopy (LIBS) techniques, has been achieved using a double-pulse technique under He gas at atmospheric pressure.
In this technique, a transversely excited atmospheric-pressure (TEA) CO2 laser (1.5 J, 200 ns) was focused onto the metal surface to induce a strong He gas plasma whilst simultaneously focussing
a Nd-doped yttrium aluminum garnet (Nd:YAG) laser (120 mJ, 8 ns), synchronized with the TEA CO2 laser, onto the metal to ablate
atoms into the resulting He gas plasma. The emission spectrum obtained shows a narrow H linewidth with low background intensity
and long lifetime emission, thereby indicating that excitation takes place via metastable He atoms. The H emission from H2O can be suppressed by a careful pretreatment involving heating the sample in a vacuum chamber.
breakdown spectroscopy (LIBS) techniques, has been achieved using a double-pulse technique under He gas at atmospheric pressure.
In this technique, a transversely excited atmospheric-pressure (TEA) CO2 laser (1.5 J, 200 ns) was focused onto the metal surface to induce a strong He gas plasma whilst simultaneously focussing
a Nd-doped yttrium aluminum garnet (Nd:YAG) laser (120 mJ, 8 ns), synchronized with the TEA CO2 laser, onto the metal to ablate
atoms into the resulting He gas plasma. The emission spectrum obtained shows a narrow H linewidth with low background intensity
and long lifetime emission, thereby indicating that excitation takes place via metastable He atoms. The H emission from H2O can be suppressed by a careful pretreatment involving heating the sample in a vacuum chamber.
Mechanism for giant electro-optic response of porphyrin J-aggregates in polymer film and aqueous solution
Fri, 2010-06-04 18:48 — Guest
Abstract
We report the dependence of the polarizability difference Δα on the orientational distribution of porphyrin J-aggregates. For quasi-one-dimensionally oriented aggregates in a polymer
film, the red shift in Y ∥ F configuration was about 2 to 3 times smaller than that in Y ∥ F configuration, where Y is the orientational direction of the J-aggregates and F is the applied AC electric field vector. For an aqueous solution where J-aggregates were three-dimensionally oriented, the
exciton band showed an electric-field-induced broadening. In addition, a red-shifted signal for two-dimensionally oriented
aggregates in the polymer film was reduced by one order of magnitude at 77K compared with that at room temperature. These
results were explained reasonably well by the molecular rearrangement model, which was applied to a variety of orientational
distributions.
film, the red shift in Y ∥ F configuration was about 2 to 3 times smaller than that in Y ∥ F configuration, where Y is the orientational direction of the J-aggregates and F is the applied AC electric field vector. For an aqueous solution where J-aggregates were three-dimensionally oriented, the
exciton band showed an electric-field-induced broadening. In addition, a red-shifted signal for two-dimensionally oriented
aggregates in the polymer film was reduced by one order of magnitude at 77K compared with that at room temperature. These
results were explained reasonably well by the molecular rearrangement model, which was applied to a variety of orientational
distributions.
All optical phase-only filtering correlation with binarized inputs by a ferroelectric liquid-crystal spatial light modulator
Fri, 2010-06-04 18:48 — Guest
Abstract
All optical phase-only filtering correlator is constructed with an optically addressed ferroelectric liquid-crystal spatial
light modulator (FSLM) for a binarized input object and a twisted-nematic liquid-crystal spatial-light modulator for a computer-generated
phase-only filter. In order to improve the discrimination capability of a phase-only filtering correlator, a binarized amplitude
with maximum contrast in a FSLM is used for an object input. The contrast of binarized intensities can be maximized by adjusting
the rotation angles of a FSLM and polarizers. The threshold level of binarized input objects can be controlled by changing
the power of a laser incident on a FLSM. Experimental results with a high discrimination capability are presented to support
the numerical correlation performance.
light modulator (FSLM) for a binarized input object and a twisted-nematic liquid-crystal spatial-light modulator for a computer-generated
phase-only filter. In order to improve the discrimination capability of a phase-only filtering correlator, a binarized amplitude
with maximum contrast in a FSLM is used for an object input. The contrast of binarized intensities can be maximized by adjusting
the rotation angles of a FSLM and polarizers. The threshold level of binarized input objects can be controlled by changing
the power of a laser incident on a FLSM. Experimental results with a high discrimination capability are presented to support
the numerical correlation performance.
Growth of Ba2−xSrxNaNb5O15 thin film on La0.05Sr0.95TiO3 substrate by pulsed laser deposition
Fri, 2010-06-04 18:48 — Guest
Abstract
Ba2−x
Sr
x
NaNb5O15 thin films were prepared on La0.05Sr0.95TiO3 substrates by pulsed laser deposition. The structural and ferroelectric properties of the thin films depended on substrate
temperature (T
sub) and Sr concentration. When T
sub was fixed at 700 °C, the Ba2−x
Sr
x
NaNb5O15 (x = 0, 0.6, 1.0, and 1.4) thin films exhibited a high c-axis orientation. The thin films consisted of well-developed grains and exhibited a smooth surface. The c-axis-oriented Ba0.6Sr1.4NaNb5O15 thin film with the lowest Curie temperature also exhibited a high c-axis orientation and a P-E hysteresis loop with a high ferroelectricity at T
sub 650 °C.
Sr
x
NaNb5O15 thin films were prepared on La0.05Sr0.95TiO3 substrates by pulsed laser deposition. The structural and ferroelectric properties of the thin films depended on substrate
temperature (T
sub) and Sr concentration. When T
sub was fixed at 700 °C, the Ba2−x
Sr
x
NaNb5O15 (x = 0, 0.6, 1.0, and 1.4) thin films exhibited a high c-axis orientation. The thin films consisted of well-developed grains and exhibited a smooth surface. The c-axis-oriented Ba0.6Sr1.4NaNb5O15 thin film with the lowest Curie temperature also exhibited a high c-axis orientation and a P-E hysteresis loop with a high ferroelectricity at T
sub 650 °C.
Chaos dynamics in semiconductor lasers with polarization-rotated optical feedback
Fri, 2010-06-04 18:48 — Guest
Abstract
By using polarization-rotated optical feedback from the transverse-electric (TE) mode to the transverse-magnetic (TM) mode,
chaotic oscillations for both polarization modes are excited in a semiconductor laser. We find different correlations between
these chaotic oscillations than those found in previous studies. In this study, the dynamics are strongly dependent on their
radio-frequency (RF) components and they are divided into three RF regions. For low-pass filtered signals lower than the laser
relaxation oscillation, there is an antiphase correlation between the two polarization modes. On the other hand, the two polarization
modes have an in-phase correlation for the RF components of the high-pass filtered signals, which are higher than the relaxation
oscillation. However, no correlations were observed between the two modes for the intermediate RF components that include
the relaxation oscillation frequency.
chaotic oscillations for both polarization modes are excited in a semiconductor laser. We find different correlations between
these chaotic oscillations than those found in previous studies. In this study, the dynamics are strongly dependent on their
radio-frequency (RF) components and they are divided into three RF regions. For low-pass filtered signals lower than the laser
relaxation oscillation, there is an antiphase correlation between the two polarization modes. On the other hand, the two polarization
modes have an in-phase correlation for the RF components of the high-pass filtered signals, which are higher than the relaxation
oscillation. However, no correlations were observed between the two modes for the intermediate RF components that include
the relaxation oscillation frequency.
Visible nonlinear band-edge luminescence in ZnSe and CdS excited by a mid-infrared free-electron laser
Fri, 2010-06-04 18:48 — Guest
Abstract
Visible nonlinear band-edge luminescence in ZnSe and CdS bulk crystals was observed upon excitation by a mid-infrared free-electron
laser (mid-IR FEL) at approximately 9 mm. The emission intensity is proportional to the 74th and 45th powers of the excitation
intensity for ZnSe and CdS, respectively. For ZnSe, the temporal profile of the emission intensity does not follow the profile
of the excitation macropulse of the FEL, but sharply rises and decays only at the maximum of the macropulse profile. These
features are in marked contrast to those of a previous report, where the emission profile follows that of the macropulse,
and the emission intensity scales with the 4th power of the excitation intensity. The experimental observations were reproduced
by a numerical simulation based on impact ionization and avalanche ionization by electrons accelerated by the optical electric
field of the FEL.
laser (mid-IR FEL) at approximately 9 mm. The emission intensity is proportional to the 74th and 45th powers of the excitation
intensity for ZnSe and CdS, respectively. For ZnSe, the temporal profile of the emission intensity does not follow the profile
of the excitation macropulse of the FEL, but sharply rises and decays only at the maximum of the macropulse profile. These
features are in marked contrast to those of a previous report, where the emission profile follows that of the macropulse,
and the emission intensity scales with the 4th power of the excitation intensity. The experimental observations were reproduced
by a numerical simulation based on impact ionization and avalanche ionization by electrons accelerated by the optical electric
field of the FEL.
