Description: We investigate the influence of polarity on carrier transport in single-quantum-well and
multiple-quantum-well (MQW) light-emitting diodes (LEDs) grown on the semipolar (20¯21)
and (20¯21) orientations of free-standing GaN. For semipolar MQW LEDs with the opposite
polarity to conventional Ga-polar c-plane LEDs, the polarization-related electric field in the
QWs results in an additional energy barrier for carriers to escape the QWs. We show that
Description: DC and bipolar voltage stresses are used to isolate mechanical degradation of the movable
electrode from charging mechanism in microelectromechanical capacitive switches. Switches with
different metals as the movable electrode were investigated. In titanium switches, a shift in the
pull-in voltages is observed after dc stressing whereas no shift occurs after the bipolar stressing,
which is to be expected from charging theory. On switches with similar dielect...
Description: We demonstrate how two optical functionalities can be implemented in a single photonic crystal structure by carefully engineering dispersion in several different bands at several different wavelengths. We use the concept for optically pumped dye doped hybrid polymer band edge lasers and show how a rectangular photonic crystal lattice imprinted into the surface can provide both feedback for in-plane band edge lasing and couple pump light into the device plane...
Description: An investigation of the terahertz wave generation in multiple laser-induced air plasmas is presented.
First, it is demonstrated that the intensity of the terahertz wave increases as the number of air
plasmas increases. Second, the physical mechanism of this enhancement effect of the terahertz
generation is studied by quantitatively measuring the intensity of the generated terahertz wave as a
function of phase difference between adjacent air plasmas. It is fo...
Description: Using extreme ultraviolet XUV radiation from a high harmonic source, we observe diffraction
from a single-layer self-assembled hexagonal array of 196 1.2 nm diameter polystyrene spheres.
The Mie solution is used to predict the correct form factor for a single sphere and hence model the
intensities of the observed diffraction peaks for the first three orders. By measuring the diffraction
intensities in this way, we demonstrate a technique for obtaining the ...
Description: Multicore quantum cascade lasers with large cavities show low optical losses, high saturation
intensity, and low beam divergence. We present a four active core laser based on InGaAs–AlInAs
material system emitting at 10.5 μm. To improve thermal conductance, InP interstacks were used
to separate active regions. Selective lateral etching of the active regions was used to reduce optical
losses. Peak powers up to 4.6 W, average powers up to 310 mW, and wall-plu...
Description: A dielectric plasmonic photonic crystal for manipulating surface plasmon polariton SPP fields has
been designed, fabricated, and tested. The band structure of SPP fields inside the plasmonic photonic
crystal has been calculated using the plane wave expansion method and validated by full wave
numerical simulations. The fabricated device was characterized using our far-field SPP imaging
technique. The transmittance of incident SPP waves is about 5% at 1520 n...
Description: We propose a fiber-based system aimed at generating radially and azimuthally polarized beams over
spectral ranges of several tens of nanometers. The device is either adaptable to polychromatic
sources such as supercontinuum fiber lasers or to tunable ones optical parametric oscillator, laser
diode, etc. . A preliminary version of the system has been engineered to work in the visible portion
of the spectrum. The concept proposed here can be adapted to the in...
Description: We experimentally demonstrate an enhanced four-wave mixing FWM based on atomic coherence
in a Pr3+:Y2SiO5 crystal. By employing coherent population return and fractional stimulated Raman
adiabatic passage to prepare maximum atomic coherence in the crystal, an efficient FWM signal can
be generated. By measuring the generated FWM signal, the time-dependent atomic coherence is
monitored. Such an enhanced FWM in solids may have practical applications in nonlin...
Description: In this work a μ =−1 metamaterial MM lens for magnetic resonance imaging MRI is
demonstrated. MRI uses surface coils to detect the radio frequency rf energy absorbed and emitted
by the nuclear spins in the imaged object. The proposed MM lens manipulates the rf field detected
by these surface coils so that the coil sensitivity and spatial localization are substantially improved.
Beyond this specific application, we feel that the reported results are th...
Description: We report directional light extraction from AlGaInP thin-film resonant cavity light emitting diodes
RCLEDs with shallow photonic crystals PhCs . Diffraction of guided modes into the light
extraction cone enhances the light extraction by a factor of 2.6 compared to unstructured RCLEDs,
where the farfields still show higher directionality than Lambertian emitters. The external quantum
efficiency is 15.5% to air and 26% with encapsulation, respectively. The ...
Description: The phenomenon of tunneling manifests itself in nearly every field of physics. The ability to
distinguish a wave tunneling through a barrier from one propagating is important for a number of
applications. Here we explore the properties of the wave traveling through the band gap created by
a lattice, either as a consequence of tunneling through the barrier or due to the presence of a pass
band inside the gap. To observe the pass band for studying tunneling an...
Description: The enhanced and partially polarized output of a green light-emitting diode (LED) , in which its
InGaN/GaN quantum well (QW) couples with surface plasmons (SPs) on a surface Ag grating
structure, is demonstrated. Compared with a LED sample without flat Ag coating, the total output
intensity of an LED of SP-QW coupling can be enhanced by ~59% ( ~ 200 %) when the grating
period and groove depth are 500 and 30 nm, respectively. Also, a bottom-emission po...
Description: Heat accumulation by high repetition rate femtosecond laser irradiation inside glass generates a
much larger modification than that by a single pulse. In this study, we determined the temperature
distribution due to heat accumulation and the characteristic temperature for heat modification inside
a soda lime glass by analyzing the relationship between the radius of modification and glass
temperature. The validity of the analysis was confirmed by reproducing ...
Description: We have found experimentally that it is possible to restore the high spatial frequency of optical
images by using stimulated Brillouin scattering (SBS) with a prepulse. The Stokes wave usually has
to lose the high spatial frequency because of the necessary energy to generate the acoustic grating.
However, this problem has been resolved by using a prepulse method. We have achieved an
amplitude increase of ~41% compared to the normal SBS scheme at a spatial ...
Description: We present coherence-gated holographic imaging using a highly sensitive photorefractive PR
polymer composite as the recording medium. Due to the high sensitivity of the composite
holographic recording at intensities as low as 5 mW/cm2 allowed for a frame exposure time of only
500 ms. Motivated by regenerative medical applications, we demonstrate optical depth sectioning of
a polymer foam for use as a cell culture matrix. An axial resolution of 18 m and a ...
Description: We have experimentally demonstrated enhanced image contrast of sample fine structure in a
coherent anti-Stokes Raman scattering (CARS) microscope using liquid crystal spatial light
modulators as programmable Toraldo-style pupil phase masks. We demonstrated through modeling,
implementation, and verification of the focal intensity and phase distributions of the excitation
beams the trade-offs between improved image contrast and CARS signal levels.
Description: Elliptically polarized terahertz emission from a femtosecond laser filament in air in the forward
direction was discovered by using a wire grid polarizer and electro-optic sampling technique. The
generation mechanism could be through four-wave optical rectification or second-order optical
rectification inside the filament zone where the inversion symmetry of air is broken.
Description: Carrier capturing in GaInP/Er,O-codoped GaAs (GaAs:Er,O) /GaInP laser diodes (LDs) was
investigated by means of the threshold current density (Jth) of laser emission. The Er-doped LDs
showed laser emission of the GaAs band edge at room temperature, and its Jth increases with the Er
flow rate during the growth. In the dependence of Jth on reciprocal cavity length, the effective gain
factor of the LDs decreased by the codoping of Er and O. These results r...
Description: Pulsed microdischarge was generated in microbubbles produced by electrolysis in an electrolyte
solution without external gas feed by using a fabric-type electrode. The electrode structure not only
allowed low-voltage ignition of the atmospheric-pressure discharge in hydrogen or oxygen
containing microbubbles but also worked effectively in producing and holding the bubbles on its
surface. The generation of reactive species was verified by optical emissions fr...