235 research outputs found
Decomposition of NO studied by infrared emission and CO laser absorption
A diagnostic technique for monitoring the concentration of NO using absorption of CO laser radiation was developed and applied in a study of the decomposition kinetics of NO. Simultaneous measurements of infrared emission by NO at 5.3 microns were also made to validate the laser absorption technique. The data were obtained behind incident shocks in NO-N2O-Ar (or Kr) mixtures, with temperatures in the range 2400-4100 K. Rate constants for dominant reactions were inferred from comparisons with computer simulations of the reactive flow
Frontiers in microphotonics: tunability and all-optical control
The miniaturization of optical devices and their integration for creating adaptive and reconfigurable photonic integrated circuits requires effective platforms and methods to control light over very short distances. We present here several techniques an
Photo-induced second-order nonlinearity in stoichiometric silicon nitride waveguides
We report the observation of second-harmonic generation in stoichiometric
silicon nitride waveguides grown via low-pressure chemical vapour deposition.
Quasi-rectangular waveguides with a large cross section were used, with a
height of 1 {\mu}m and various different widths, from 0.6 to 1.2 {\mu}m, and
with various lengths from 22 to 74 mm. Using a mode-locked laser delivering
6-ps pulses at 1064 nm wavelength with a repetition rate of 20 MHz, 15% of the
incoming power was coupled through the waveguide, making maximum average powers
of up to 15 mW available in the waveguide. Second-harmonic output was observed
with a delay of minutes to several hours after the initial turn-on of pump
radiation, showing a fast growth rate between 10 to 10 s,
with the shortest delay and highest growth rate at the highest input power.
After this first, initial build-up, the second-harmonic became generated
instantly with each new turn-on of the pump laser power. Phase matching was
found to be present independent of the used waveguide width, although the
latter changes the fundamental and second-harmonic phase velocities. We address
the presence of a second-order nonlinearity and phase matching, involving an
initial, power-dependent build-up, to the coherent photogalvanic effect. The
effect, via the third-order nonlinearity and multiphoton absorption leads to a
spatially patterned charge separation, which generates a spatially periodic,
semi-permanent, DC-field-induced second-order susceptibility with a period that
is appropriate for quasi-phase matching. The maximum measured second-harmonic
conversion efficiency amounts to 0.4% in a waveguide with 0.9 x 1 {\mu}m
cross section and 36 mm length, corresponding to 53 {\mu}W at 532 nm with 13 mW
of IR input coupled into the waveguide. The according amounts to
3.7 pm/V, as retrieved from the measured conversion efficiency.Comment: 20 pages, 10 figure
Liquid-infiltrated photonic crystals - enhanced light-matter interactions for lab-on-a-chip applications
Optical techniques are finding widespread use in analytical chemistry for
chemical and bio-chemical analysis. During the past decade, there has been an
increasing emphasis on miniaturization of chemical analysis systems and
naturally this has stimulated a large effort in integrating microfluidics and
optics in lab-on-a-chip microsystems. This development is partly defining the
emerging field of optofluidics. Scaling analysis and experiments have
demonstrated the advantage of micro-scale devices over their macroscopic
counterparts for a number of chemical applications. However, from an optical
point of view, miniaturized devices suffer dramatically from the reduced
optical path compared to macroscale experiments, e.g. in a cuvette. Obviously,
the reduced optical path complicates the application of optical techniques in
lab-on-a-chip systems. In this paper we theoretically discuss how a strongly
dispersive photonic crystal environment may be used to enhance the light-matter
interactions, thus potentially compensating for the reduced optical path in
lab-on-a-chip systems. Combining electromagnetic perturbation theory with
full-wave electromagnetic simulations we address the prospects for achieving
slow-light enhancement of Beer-Lambert-Bouguer absorption, photonic band-gap
based refractometry, and high-Q cavity sensing.Comment: Invited paper accepted for the "Optofluidics" special issue to appear
in Microfluidics and Nanofluidics (ed. Prof. David Erickson). 11 pages
including 8 figure
Field test of quantum key distribution in the Tokyo QKD Network
A novel secure communication network with quantum key distribution in a
metropolitan area is reported. Different QKD schemes are integrated to
demonstrate secure TV conferencing over a distance of 45km, stable long-term
operation, and application to secure mobile phones.Comment: 21 pages, 19 figure
Relational Thread-Modular Abstract Interpretation Under Relaxed Memory Models
International audienceWe address the verification problem of numeric properties in many-threaded concurrent programs under weakly consistent memory models, especially TSO. We build on previous work that proposed an abstract interpretation method to analyse these programs with rela-tional domains. This method was not sufficient to analyse more than two threads in a decent time. Our contribution here is to rely on a rely-guarantee framework with automatic inference of thread interferences to design an analysis with a thread-modular approach and describe re-lational abstractions of both thread states and interferences. We show how to adapt the usual computing procedure of interferences to the additional issues raised by weakly consistent memories. We demonstrate the precision and the performance of our method on a few examples, operating a prototype analyser that verifies safety properties like mutual exclusion. We discuss how weak memory models affect the scalability results compared to a sequentially consistent environment
Moving liquids with light: Photoelectrowetting on semiconductors
Liquid transport in microchip-based systems is important in many areas such
as Laboratory-on-a-chip, Microfluidics and Optofluidics. Actuation of liquids
in such systems is usually achieved using either mechanical displacement11 or
via energy conversion e.g. electrowetting which modifies wetting. However, at
the moment there is no clear way of actuating a liquid using light. Here, by
linking semiconductor physics and wetting phenomenon a brand new effect
"photoelectrowetting" is demonstrated for a droplet of conducting liquid
resting on an insulator-semiconductor stack. Optical generation of carriers in
the space-charge region of the underlying semiconductor alters the capacitance
of the insulator-semiconductor stack; the result of this is a modification of
the wetting contact angle of the droplet upon illumination. The effect is
demonstrated using commercial silicon wafers, both n- and p-type having a
doping range spanning four orders of magnitude (6\times1014-8\times1018 cm-3),
coated with a commercial fluoropolymer insulating film (Teflon\textregistered).
Impedance measurements confirm that the observations are semiconductor
space-charge related effects. The impact of the work could lead to new
silicon-based technologies in the above mentioned areas
Differences in meristem size and expression of branching genes are associated with variation in panicle phenotype in wild and domesticated African rice
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