In this paper, we present the design and the fabrication method for high DC bias voltage photoconductive semiconductor
switch (PCSS). By employing a low temperature grown molecular beam epitaxial GaAs (LT-MBE GaAs) and a proper
protection coating to prevent air breakdown, the DC bias electric field can be significantly increased. Such a PCSS
structure can effectively achieve a low DC dark current in a high voltage pulse generation system with smaller PCSS
sizes. DC bias capability also eliminates the need of complicated synchronization. The application of high DC bias field
PCSS will also be discussed.
Microwave assisted synthesis of crystalline FeBO3 powder is investigated in a multimode cavity at 2.45GHz as a
possible method for faster synthesis. An Alumina-SiC susceptor enclosure was placed inside the cavity to overcome poor
microwave absorption of the precursor at low temperatures. Enhanced diffusion was observed with appropriate precursor
viscosity at reaction temperature. Less than 8 hours was found enough to complete FeBO3 synthesis, as compared with
more than 20 hours of synthesis using conventional muffle oven. Microwave enhanced diffusion was not obvious with
too high viscosity and eventually leveled by thermal diffusion with too low viscosity. The microwave synthesized FeBO3
particles were found more rhombohedral and smaller than conventional furnace synthesized ones, thus are inherently
more suitable as optical composite materials.
KEYWORDS: Microwave radiation, Gas lasers, Absorption, Infrared spectroscopy, Near infrared, Chemical detection, Spectroscopy, Signal detection, Solar concentrators, Infrared radiation
In this paper, recent works of buried chemical detection system by stimulating and enhancing spectroscopic
signatures with multi-frequency excitations are discussed. In this detection system, those multiple excitations,
including DC electric field, microwave, CO2 laser illumination and infrared radiation, are utilized and each of
them plays a unique role. The Microwave could effectively increase the buried chemicals' evaporation rate from
the source. The gradient DC electric field, generated by a Van De Graaff generator, not only serves as a vapor
accelerator for efficiently expediting the transportation process of the vapor release from the buried chemicals,
but also acts as a vapor concentrator for increasing the chemical concentrations in the detection area, which
enables the trace level chemical detection. Similarly, CO2 laser illumination, which behaves as another type
vapor accelerator, could also help to release the vapors adsorbed on the soil surface to the air rapidly. Finally, the
stimulated and enhanced vapors released into the air are detected by the infrared (IR) spectroscopic fingerprints.
Our theoretical and experimental results demonstrate that more than 20-fold increase of detection signal can be
achieved by using those proposed technology.
In this paper, we have reviewed our recent works on IR supercontinuum generation (SCG) and its applications. First, we
provide a brief review on the physical mechanism of the supercontinuum generation. Second, the advance of SCG in
single crystal sapphire fibers is reviewed and introduced. In particular, we discussed how to fabricate thinned sapphire
fiber and use it for high efficiency SCG. Finally, experimental results of chemical analysis with supercontinuum source
are reviewed.
In this paper, the separation of transmitted and diffused light beams in a scattering medium by a magneto-optical ultrafast
switch is investigated. The magneto-optical switch previously developed by the authors is capable of 1 ns switching
speed and has a 1 mm clear aperture. The diffused light beams and ballistic beams in a scattering medium are simulated
in the lab by two beam paths. One beam is delayed from the other to simulate the diffused light beam and the ballistic
beam, respectively. The magneto-optical switch is synchronized with the required delay to the laser pulse to keep only
the ballistic beam, acting as an ultrafast light gate. The concept is demonstrated with a 532nm Q-switched pulsed laser.
In this paper, the application of a broadband spatially coherent IR supercontinuum source to the biomedical imaging and
detection is presented. New IR material is proposed to generate Mid-IR supercontinuum above 4um, which was previously
difficult due to inherent material absorption. Broad Mid-IR supercontinuum is numerically shown to be possible
with one single wavelength pump in appropriate fiber structure.
Mid-IR broadband sources are very useful in IR Optical
Coherence Tomography (OCT) and spectroscopy in biomedical materials, due to the rich absorption structures the
Mid-IR region. Broadband Mid-IR source is better than single wavelength tunable source, such as Quantum Cascaded Lasers
(QCL), for faster analysis speed, since slow scan is not required.
In this paper, some of our recent works on the design of different types of nanostructured surfaces, the
terahertz generation, terahertz lenses, and terahertz metamaterials are reviewed and discussed. The
mechanism behind the terahertz radiation is the photoelectric emission effect, which leads to the
oscillating motions of emitted electrons and are affected by the electric field inside the metal.
Furthermore, by using those nanostructured surfaces, terahertz lenses, which are due to the excitation
of surface plasmons, and terahertz metamaterials, which results from the effective inductor-capacitor
resonator, are also presented.
In this paper, we have reviewed our recent works on IR supercontinuum generation (SCG) and its applications. First, we
provide a brief introduction on the motivations of the proposed effort. Second, the work of SCG in single crystal
sapphire fibers is reviewed. Third, in addition to single crystal sapphire fibers, the method, the process, and the results
of fabricating other IR waveguides are presented. Fourth, a quantitative simulation on the supercontinuum generation
with the new IR waveguide is provided, which shows that it is possible to generate SCG beyond 5 microns. To the best
knowledge of authors, this is the longest SCG reported so far. Finally, more experimental results of chemical analysis
with supercontinuum source are presented.
An ultrafast light-activated magneto-optical modulator is demonstrated in this paper. This modulator is capable of 1 ns
modulation speed and has a 1 mm clear aperture. The design of the modulator incorporates a photoconductive switch and
enables a synchronized and jitter-free operation, which eliminates the need of any electrical or optical delay lines. These
features make the current design very attractive in typical free-space pulse laser applications. To the authors' knowledge,
this is so far the fastest MO modulator with such aperture size that has been reported.
Because the efficiency of THz generation in air plasma is quite low, the residual power of input beam after THz
radiation is generated in air plasma remains almost the same. A new method, multiple air plasmas, is proposed. The
residual power can be used to induce other air plasmas and generate THz radiation again. The multiple air plasmas
method provides a potential way for the development of the intense THz source. The preliminary experimental
results confirm the theoretical prediction. The multiple air plasmas generated THz can be very useful for remote
THz generation and standoff detection.
In this paper, the two different mechanisms of supercontinuum generation in single crystal sapphire fibers according to
fiber lengths longer and shorter than dispersion length are theoretically and experimentally investigated. When the fiber
length is shorter than the dispersion length, self-phase modulation is the dominant factor for supercontinuum broadening.
A broad spectrum ranging from near-IR (1.2 μm) to the lower end of mid-IR (2.8 μm) is obtained. But, when the fiber
length is longer than dispersion length, soliton-related dynamics with self-phase modulation is the dominant factor for
supercontinuum. We further demonstrate that supercontinuum in a sapphire fiber can extend beyond the range of silica
fibers by showing the spectrum from 2 μm to 3.2 μm. Also, we successfully apply the supercontinuum source generated
from a sapphire fiber to IR spectroscopy. The spectra of pseudo-TNT chemical measured using our own supercontinuum
source is in good agreement with those obtained by FTIR. Supercontinuum generation using a sapphire fiber, which has
high damage threshold and broad transmission ranges can be used in many applications such as IR spectroscopy,
broadband LADAR, remote sensing, and multi-spectrum free space communications.
We synthesized a new magneto-optical nanoparticle material Bi1.8Y 1.2Fe4Ga1O12 (BYIGG) with
substitution of gallium by iron. It was prepared using coprecipitation and annealing processes. High
Energy ball-milling was used to mill the nanoparticle to tens of nanometer range. The thin-film coated
shows improvement of transmittance because of the substitution. A simple model for scattering and
Faraday Effect was used to calculate the transmittance and Faraday Rotation angle, which shows have
a good match with the known experimental result.
In this presentation, a simple patchwork to the classical mode matching method (MMM) is proposed to analyze rib ARROWs. MMM gives the modal effective index and the lateral part of modal power loss, and the total modal loss is obtained by including the vertical part which is estimated by a simple yet physical method described here. The simplified MMM (SMMM) is also presented to analyze the effect of TE-TM couplings. Simulation results of selected rib ARROW structures are discussed and compared with those obtained by the Effective Index Method (EIM).
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