368 research outputs found
Demonstration of superluminal effects in an absorptionless, non-reflective system
We present an experimental and theoretical study of a simple, passive system
consisting of a birefringent, two-dimensional photonic crystal and a polarizer
in series, and show that superluminal dispersive effects can arise even though
no incident radiation is absorbed or reflected. We demonstrate that a vector
formulation of the Kramers-Kronig dispersion relations facilitates an
understanding of these counter-intuitive effects.Comment: 6 pages, 3 figures, accepted on Physical Review Letter
Examining the relationship between student performance and video interactions
In this work, we attempted to predict student performance on a suite of
laboratory assessments using students' interactions with associated
instructional videos. The students' performance is measured by a graded
presentation for each of four laboratory presentations in an introductory
mechanics course. Each lab assessment was associated with between one and three
videos of instructional content. Using video clickstream data, we define
summary features (number of pauses, seeks) and contextual information (fraction
of time played, in-semester order). These features serve as inputs to a
logistic regression (LR) model that aims to predict student performance on the
laboratory assessments. Our findings show that LR models are unable to predict
student performance. Adding contextual information did not change the model
performance. We compare our findings to findings from other studies and explore
caveats to the null-result such as representation of the features, the
possibility of underfitting, and the complexity of the assessment.Comment: 4 pages, 1 figure, submitted to the PERC 2018 proceeding
Fast light, slow light, and phase singularities: a connection to generalized weak values
We demonstrate that Aharonov-Albert-Vaidman (AAV) weak values have a direct
relationship with the response function of a system, and have a much wider
range of applicability in both the classical and quantum domains than
previously thought. Using this idea, we have built an optical system, based on
a birefringent photonic crystal, with an infinite number of weak values. In
this system, the propagation speed of a polarized light pulse displays both
superluminal and slow light behavior with a sharp transition between the two
regimes. We show that this system's response possesses two-dimensional,
vortex-antivortex phase singularities. Important consequences for optical
signal processing are discussed.Comment: 9 pages, 4 figures, accepted in Physical Review Letters (2003
Real-time Spectroscopy with Sub-GHz Resolution using Amplified Dispersive Fourier Transformation
Dispersive Fourier transformation is a powerful technique in which spectral
information is mapped into the time domain using chromatic dispersion. It
replaces a spectrometer with an electronic digitizer, and enables real-time
spectroscopy. The fundamental problem in this technique is the trade-off
between the detection sensitivity and spectral resolution, a limitation set by
the digitizer's bandwidth. This predicament is caused by the power loss
associated with optical dispersion. We overcome this limitation using Raman
amplified spectrum-to-time transformation. An extraordinary loss-less -11.76
ns/nm dispersive device is used to demonstrate single-shot gas absorption
spectroscopy with 950 MHz resolution--a record in real-time spectroscopy.Comment: The following article has been accepted by Applied Physics Letter
Microwave measurements of the photonic bandgap in a two-dimensional photonic crystal slab
We have measured the photonic bandgap in the transmission of microwaves
through a two-dimensional photonic crystal slab. The structure was constructed
by cementing acrylic rods in a hexagonal closed-packed array to form
rectangular stacks. We find a bandgap centered at approximately 11 GHz, whose
depth, width and center frequency vary with the number of layers in the slab,
angle of incidence and microwave polarization.Comment: 8 pages, 3 figures, submitted to Journal of Applied Physic
Photonic crystal polarizers and polarizing beam splitters
We have experimentally demonstrated polarizers and polarizing beam splitters
based on microwave-scale two-dimensional photonic crystals. Using polarized
microwaves within certain frequency bands, we have observed a squared-sinusoid
(Malus) transmission law when using the photonic crystal as a polarizer. The
photonic crystal also functions as a polarizing beamsplitter; in this
configuration it can be engineered to split incident polarizations in either
order, making it more versatile than conventional, Brewster-angle
beamsplitters.Comment: 7 pages, 3 figures, published Journal Applied Physics 93, 9429 (2003
Noise figure and photon probability distribution in Coherent Anti-Stokes Raman Scattering (CARS)
The noise figure and photon probability distribution are calculated for
coherent anti-Stokes Raman scattering (CARS) where an anti-Stokes signal is
converted to Stokes. We find that the minimum noise figure is ~ 3dB.Comment: 2 page
Rare frustration of optical supercontinuum generation
Extremely large, rare events arise in various systems, often representing a
defining character of their behavior. Another class of extreme occurrences,
unexpected failures, may appear less important, but in applications demanding
stringent reliability, the rare absence of an intended effect can be
significant. Here, we report the observation of rare gaps in supercontinuum
pulse trains, events we term rogue voids. These pulses of unusually small
spectral bandwidth follow a reverse-heavy-tailed statistical form. Previous
analysis has shown that rogue waves, the opposite extremes in supercontinuum
generation, arise by stochastic enhancement of nonlinearity. In contrast, rogue
voids appear when spectral broadening is suppressed by competition between
pre-solitonic features within the modulation-instability band. This suppression
effect can also be externally induced with a weak control pulse.Comment: 17 pages, 5 figure
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