11,242 research outputs found
Tunable Circularly Polarized Terahertz Radiation from Magnetized Gas Plasma
It is shown, by simulation and theory, that circularly or elliptically
polarized terahertz radiation can be generated when a static magnetic (B) field
is imposed on a gas target along the propagation direction of a two-color laser
driver. The radiation frequency is determined by
, where is the
plasma frequency and is the electron cyclotron frequency. With the
increase of the B field, the radiation changes from a single-cycle broadband
waveform to a continuous narrow-band emission. In high-B-field cases, the
radiation strength is proportional to . The B field
provides a tunability in the radiation frequency, spectrum width, and field
strength.Comment: 6 pages, 5 figure
Absence of correlation between built-in electric dipole moment and quantum Stark effect in InAs/GaAs self-assembled quantum dots
We report significant deviations from the usual quadratic dependence of the
ground state interband transition energy on applied electric fields in
InAs/GaAs self-assembled quantum dots. In particular, we show that conventional
second-order perturbation theory fails to correctly describe the Stark shift
for electric field below kV/cm in high dots. Eight-band calculations demonstrate this effect is predominantly due to
the three-dimensional strain field distribution which for various dot shapes
and stoichiometric compositions drastically affects the hole ground state. Our
conclusions are supported by two independent experiments.Comment: 4 pages, 4 figure
Building a 3.5 m prototype interferometer for the Q & A vacuum birefringence experiment and high precision ellipsometry
We have built and tested a 3.5 m high-finesse Fabry-Perot prototype
inteferometer with a precision ellipsometer for the QED test and axion search
(Q & A) experiment. We use X-pendulum-double-pendulum suspension designs and
automatic control schemes developed by the gravitational-wave detection
community. Verdet constant and Cotton-Mouton constant of the air are measured
as a test. Double modulation with polarization modulation 100 Hz and
magnetic-field modulation 0.05 Hz gives 10^{-7} rad phase noise for a 44-minute
integration.Comment: This draft has been presented in the 5th Edoardo Amaldi Conference on
Gravitational Wave
Laser opacity in underdense preplasma of solid targets due to quantum electrodynamics effects
We investigate how next-generation laser pulses at 10 PW 200 PW interact
with a solid target in the presence of a relativistically underdense preplasma
produced by amplified spontaneous emission (ASE). Laser hole boring and
relativistic transparency are strongly restrained due to the generation of
electron-positron pairs and -ray photons via quantum electrodynamics
(QED) processes. A pair plasma with a density above the initial preplasma
density is formed, counteracting the electron-free channel produced by the hole
boring. This pair-dominated plasma can block the laser transport and trigger an
avalanche-like QED cascade, efficiently transfering the laser energy to
photons. This renders a 1--scalelength, underdense preplasma
completely opaque to laser pulses at this power level. The QED-induced opacity
therefore sets much higher contrast requirements for such pulse in solid-target
experiments than expected by classical plasma physics. Our simulations show for
example, that proton acceleration from the rear of a solid with a preplasma
would be strongly impaired.Comment: 5 figure
Anomalous quantum confined Stark effects in stacked InAs/GaAs self-assembled quantum dots
Vertically stacked and coupled InAs/GaAs self-assembled quantum dots (SADs)
are predicted to exhibit a strong non-parabolic dependence of the interband
transition energy on the electric field, which is not encountered in single SAD
structures nor in other types of quantum structures. Our study based on an
eight-band strain-dependent Hamiltonian indicates that
this anomalous quantum confined Stark effect is caused by the three-dimensional
strain field distribution which influences drastically the hole states in the
stacked SAD structures.Comment: 4 pages, 4 figure
Q & A Experiment to Search for Vacuum Dichroism, Pseudoscalar-Photon Interaction and Millicharged Fermions
A number of experiments are underway to detect vacuum birefringence and
dichroism -- PVLAS, Q & A, and BMV. Recently, PVLAS experiment has observed
optical rotation in vacuum by a magnetic field (vacuum dichroism). Theoretical
interpretations of this result include a possible pseudoscalar-photon
interaction and the existence of millicharged fermions. Here, we report the
progress and first results of Q & A (QED [quantum electrodynamics] and Axion)
experiment proposed and started in 1994. A 3.5-m high-finesse (around 30,000)
Fabry-Perot prototype detector extendable to 7-m has been built and tested. We
use X-pendulums and automatic control schemes developed by the
gravitational-wave detection community for mirror suspension and cavity
control. To polarize the vacuum, we use a 2.3-T dipole permanent magnet, with
27-mm-diameter clear borehole and 0.6-m field length,. In the experiment, the
magnet is rotated at 5-10 rev/s to generate time-dependent polarization signal
with twice the rotation frequency. Our
ellipsometer/polarization-rotation-detection-system is formed by a pair of
Glan-Taylor type polarizing prisms with extinction ratio lower than 10-8
together with a polarization modulating Faraday Cell with/without a quarter
wave plate. We made an independent calibration of our apparatus by performing a
measurement of gaseous Cotton-Mouton effect of nitrogen. We present our first
experimental results and give a brief discussion of our experimental limit on
pseudo-scalar-photon interaction and millicharged fermions.Comment: 21 pages, 13 figures, submitted to Modern Physics Letter
Diagrammatic approach to coherent backscattering of laser light by cold atoms: Double scattering revisited
We present a diagrammatic derivation of the coherent backscattering spectrum
from two two-level atoms using the pump-probe approach, wherein the multiple
scattering signal is deduced from single-atom responses, and provide a physical
interpretation of the single-atom building blocks.Comment: 16 pages, 7 figure
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