6,037 research outputs found
Phase-Insensitive Scattering of Terahertz Radiation
The nonlinear interaction between Near-Infrared (NIR) and Terahertz pulses is
principally investigated as a means for the detection of radiation in the
hardly accessible THz spectral region. Most studies have targeted second-order
nonlinear processes, given their higher efficiencies, and only a limited number
have addressed third-order nonlinear interactions, mainly investigating
four-wave mixing in air for broadband THz detection. We have studied the
nonlinear interaction between THz and NIR pulses in solid-state media
(specifically diamond), and we show how the former can be frequency-shifted up
to UV frequencies by the scattering from the nonlinear polarisation induced by
the latter. Such UV emission differs from the well-known electric-field-induced
second harmonic (EFISH) one, as it is generated via a phase-insensitive
scattering, rather than a sum- or difference-frequency four-wave-mixing
process
Coherent control of plasma dynamics
Coherent control of a system involves steering an interaction to a final
coherent state by controlling the phase of an applied field. Plasmas support
coherent wave structures that can be generated by intense laser fields. Here,
we demonstrate the coherent control of plasma dynamics in a laser wakefield
electron acceleration experiment. A genetic algorithm is implemented using a
deformable mirror with the electron beam signal as feedback, which allows a
heuristic search for the optimal wavefront under laser-plasma conditions that
is not known a priori. We are able to improve both the electron beam charge and
angular distribution by an order of magnitude. These improvements do not simply
correlate with having the `best' focal spot, since the highest quality vacuum
focal spot produces a greatly inferior electron beam, but instead correspond to
the particular laser phase that steers the plasma wave to a final state with
optimal accelerating fields
Modelling Quantum Mechanics by the Quantumlike Description of the Electric Signal Propagation in Transmission Lines
It is shown that the transmission line technology can be suitably used for
simulating quantum mechanics. Using manageable and at the same time
non-expensive technology, several quantum mechanical problems can be simulated
for significant tutorial purposes. The electric signal envelope propagation
through the line is governed by a Schrodinger-like equation for a complex
function, representing the low-frequency component of the signal, In this
preliminary analysis, we consider two classical examples, i.e. the Frank-Condon
principle and the Ramsauer effect
Laser-Induced Linear Electron Acceleration in Free Space
Linear acceleration in free space is a topic that has been studied for over
20 years, and its ability to eventually produce high-quality, high energy
multi-particle bunches has remained a subject of great interest. Arguments can
certainly be made that such an ability is very doubtful. Nevertheless, we chose
to develop an accurate and truly predictive theoretical formalism to explore
this remote possibility in a computational experiment. The formalism includes
exact treatment of Maxwell's equations, exact relativistic treatment of the
interaction among the multiple individual particles, and exact treatment of the
interaction at near and far field. Several surprising results emerged. For
example, we find that 30 keV electrons (2.5% energy spread) can be accelerated
to 7.7 MeV (2.5% spread) and to 205 MeV (0.25% spread) using 25 mJ and 2.5 J
lasers respectively. These findings should hopefully guide and help develop
compact, high-quality, ultra-relativistic electron sources, avoiding
conventional limits imposed by material breakdown or structural constraints.Comment: Supplementary Information starts on pg 1
Matterwave Transport Without Transit
Classically it is impossible to have transport without transit, i.e., if the
points one, two and three lie sequentially along a path then an object moving
from one to three must, at some point in time, be located at two. However, for
a quantum particle in a three-well system it is possible to transport the
particle between wells one and three such that the probability of finding it at
any time in the classically accessible state in well two is negligible. We
consider theoretically the analogous scenario for a Bose-Einstein condensate
confined within a three well system. In particular, we predict the adiabatic
transportation of an interacting Bose-Einstein condensate of 2000 Li atoms from
well one to well three without transiting the allowed intermediate region. To
an observer of this macroscopic quantum effect it would appear that, over a
timescale of the order of one second, the condensate had transported, but not
transited, a macroscopic distance of 20 microns between wells one and three.Comment: 6 pages, 4 figure
How to estimate the differential acceleration in a two-species atom interferometer to test the equivalence principle
We propose a scheme for testing the weak equivalence principle (Universality
of Free Fall) using an atom-interferometric measurement of the local
differential acceleration between two atomic species with a large mass ratio as
test masses. A apparatus in free fall can be used to track atomic free-fall
trajectories over large distances. We show how the differential acceleration
can be extracted from the interferometric signal using Bayesian statistical
estimation, even in the case of a large mass and laser wavelength difference.
We show that this statistical estimation method does not suffer from
acceleration noise of the platform and does not require repeatable experimental
conditions. We specialize our discussion to a dual potassium/rubidium
interferometer and extend our protocol with other atomic mixtures. Finally, we
discuss the performances of the UFF test developed for the free-fall (0-g)
airplane in the ICE project (\verb"http://www.ice-space.fr"
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