1,180 research outputs found
Longitudinal Laser Shaping in Laser Wakefield Accelerators
We study the energetics of wake excitation during the laser-plasma
interaction in application to laser wakefield accelerators. We find that both
the wake amplitude and the accelerating efficiency (transformer ratio) can be
maximized by properly shaping the longitudinal profile of the driving laser
pulse. The corresponding family of laser pulse shapes is derived in the
nonlinear regime of laser-plasma interaction. Such shapes provide theoretical
upper limit on the magnitude of the wakefield and efficiency by allowing for
uniform photon deceleration inside the laser pulse. We also construct realistic
optimal pulse shapes that can be produced in finite-bandwidth laser systems.Comment: 4 pages, 3 figures, submitted to Physical Review Letter
Pandemonium: An Evolution of Steel Pans and its Place in Music Education
This thesis is aimed at researching the development, benefits, and drawbacks of steel drums, also known as steel pans and even more commonly known amongst Trinidadians as “pans.” Steel pans are relatively new instruments having come about in the last century. They are recognized instruments with immense cultural identity on the Caribbean islands of Trinidad and Tobago. Steel bands have been well established in the United States and around the globe with the help of various pan players who have cultivated an interest in these instruments. Their popularity appears to be infectious. Using research conducted from previous studies as well as a survey distributed to a population of music educators, steel bands and their contribution towards music education is discussed in its entirety
Electromagnetic cascade in high energy electron, positron, and photon interactions with intense laser pulses
The interaction of high energy electrons, positrons, and photons with intense
laser pulses is studied in head-on collision geometry. It is shown that
electrons and/or positrons undergo a cascade-type process involving multiple
emissions of photons. These photons can consequently convert into
electron-positron pairs. As a result charged particles quickly lose their
energy developing an exponentially decaying energy distribution, which
suppresses the emission of high energy photons, thus reducing the number of
electron-positron pairs being generated. Therefore, this type of interaction
suppresses the development of the electromagnetic avalanche-type discharge,
i.e., the exponential growth of the number of electrons, positrons, and photons
does not occur in the course of interaction. The suppression will occur when 3D
effects can be neglected in the transverse particle orbits, i.e., for
sufficiently broad laser pulses with intensities that are not too extreme. The
final distributions of electrons, positrons, and photons are calculated for the
case of a high energy e-beam interacting with a counter-streaming, short
intense laser pulse. The energy loss of the e-beam, which requires a
self-consistent quantum description, plays an important role in this process,
as well as provides a clear experimental observable for the transition from the
classical to quantum regime of interaction.Comment: 13 pages, 7 figure
High-sensitivity plasma density retrieval in a common-path second-harmonic interferometer through simultaneous group and phase velocity measurement
Precise measurements of the plasma density in ionized gas cells and discharged capillaries are critical to the design and operation of plasma-based accelerators, active plasma lenses, and plasma-based radiation sources. In this manuscript, a spectral-domain common-path second-harmonic interferometer is upgraded with the simultaneous measurement of the group and phase velocity, allowing for high-sensitivity density characterization (from the phase velocity advance) without the need for phase tracking from zero-density (enabled by the group velocity delay). The technique is applied to 1.5-cm-long plasma structures, without density ambiguity in parameter scans with >2π phase jumps. The single-shot sensitivity in phase retrieval is demonstrated at 63 mrad, equivalent to a density-length product of 1.8·1015 cm -2 . This is an improvement of ×45 compared to group velocity analysis alone
Experimental observation of nonlinear Thomson scattering
A century ago, J. J. Thomson showed that the scattering of low-intensity
light by electrons was a linear process (i.e., the scattered light frequency
was identical to that of the incident light) and that light's magnetic field
played no role. Today, with the recent invention of ultra-high-peak-power
lasers it is now possible to create a sufficient photon density to study
Thomson scattering in the relativistic regime. With increasing light intensity,
electrons quiver during the scattering process with increasing velocity,
approaching the speed of light when the laser intensity approaches 10^18
W/cm^2. In this limit, the effect of light's magnetic field on electron motion
should become comparable to that of its electric field, and the electron mass
should increase because of the relativistic correction. Consequently, electrons
in such high fields are predicted to quiver nonlinearly, moving in figure-eight
patterns, rather than in straight lines, and thus to radiate photons at
harmonics of the frequency of the incident laser light, with each harmonic
having its own unique angular distribution. In this letter, we report the first
ever direct experimental confirmation of these predictions, a topic that has
previously been referred to as nonlinear Thomson scattering. Extension of these
results to coherent relativistic harmonic generation may eventually lead to
novel table-top x-ray sources.Comment: including 4 figure
Optimized laser pulse profile for efficient radiation pressure acceleration of ions
The radiation pressure acceleration regime of laser ion acceleration requires
high intensity laser pulses to function efficiently. Moreover the foil should
be opaque for incident radiation during the interaction to ensure maximum
momentum transfer from the pulse to the foil, which requires proper matching of
the target to the laser pulse. However, in the ultrarelativistic regime, this
leads to large acceleration distances, over which the high laser intensity for
a Gaussian laser pulse must be maintained. It is shown that proper tailoring of
the laser pulse profile can significantly reduce the acceleration distance,
leading to a compact laser ion accelerator, requiring less energy to operate.Comment: 10 pages, 4 figure
Nonlinear evolution of the plasma beatwave: Compressing the laser beatnotes via electromagnetic cascading
The near-resonant beatwave excitation of an electron plasma wave (EPW) can be
employed for generating the trains of few-femtosecond electromagnetic (EM)
pulses in rarefied plasmas. The EPW produces a co-moving index grating that
induces a laser phase modulation at the difference frequency. The bandwidth of
the phase-modulated laser is proportional to the product of the plasma length,
laser wavelength, and amplitude of the electron density perturbation. The laser
spectrum is composed of a cascade of red and blue sidebands shifted by integer
multiples of the beat frequency. When the beat frequency is lower than the
electron plasma frequency, the red-shifted spectral components are advanced in
time with respect to the blue-shifted ones near the center of each laser
beatnote. The group velocity dispersion of plasma compresses so chirped
beatnotes to a few-laser-cycle duration thus creating a train of sharp EM
spikes with the beat periodicity. Depending on the plasma and laser parameters,
chirping and compression can be implemented either concurrently in the same, or
sequentially in different plasmas. Evolution of the laser beatwave end electron
density perturbations is described in time and one spatial dimension in a
weakly relativistic approximation. Using the compression effect, we demonstrate
that the relativistic bi-stability regime of the EPW excitation [G. Shvets,
Phys. Rev. Lett. 93, 195004 (2004)] can be achieved with the initially
sub-threshold beatwave pulse.Comment: 13 pages, 11 figures, submitted to Physical Review
Correlation of the Waldron and Mississinewa Formations
Indiana Geological Survey Bulletin 3Silurian and Devonian outcrops of Indiana are divided roughly into two areas, northern and southeastern Indiana. The bedrock of the northern area is largely covered by glacial drift, whereas the bedrock of the southeastern area is well exposed. These two areas are separated by an intervening zone which is blanketed completely by glacial drift. Although accurate and detailed work has been done on the Silurian and Devonian outcrops of the state, the formations of the two areas have never been correlated.
The Silurian and Devonian formations in Indiana dip off the Cincinnati and Kankakee Arches into the Michigan Basin and the Eastern Interior Basin. The formations are difficult to trace in subsurface studies, because they are composed of a series of gradational limestones, dolomites, and calcareous siltstones. The surface formations have not been recognized in the subsurface strata. Some of the subsurface beds cannot be correlated with the outcropping beds, because additional sediments deposited in the basin do not appear on the arches.
The Silurian-Devonian contact lacks identifying characteristics over much of the area, and, for this reason, many subsurface reports have considered both systems as one unit. The writers believe that accurate determinations of thickening, thinning, and pinching-out of the Silurian and Devonian formations on the flanks of the arches would be of great assistance in future prospecting for oil.
These two problems, the geology of the arches and the geology of the basins, go hand in hand. Additional subsurface correlation studies are needed to clarify the Silurian and Devonian stratigraphy of Indiana.Indiana Department of Conservatio
- …