1,415 research outputs found
Negative refraction with tunable absorption in an active dense gas of atoms
Applications of negative index materials (NIM) presently are severely limited
by absorption. Next to improvements of metamaterial designs, it has been
suggested that dense gases of atoms could form a NIM with negligible losses. In
such gases, the low absorption is facilitated by quantum interference. Here, we
show that additional gain mechanisms can be used to tune and effectively remove
absorption in a dense gas NIM. In our setup, the atoms are coherently prepared
by control laser fields, and further driven by a weak incoherent pump field to
induce gain. We employ nonlinear optical Bloch equations to analyze the optical
response. Metastable Neon is identified as a suitable experimental candidate at
infrared frequencies to implement a lossless active negative index material.Comment: 10 pages, 9 figure
Radiation spectra of laser-driven quantum relativistic electrons
A procedure to calculate the radiation spectrum emitted by an arbitrarily
prepared Dirac wave packet is developed. It is based on the Dirac charge
current and classical electrodynamic theory. Apart from giving absolute
intensity values, it is exact in terms of relativistic retardation effects and
angular dependence. We employ a laser driven free electron to demonstrate the
advantages of our method as compared to traditional ones that merely rely on
the Fourier transform of the dipole operator's expectation value. Classical
reference calculations confirm the results obtained for the low-frequency part
of the spectrum, especially in terms of the observed red-shifts, which clearly
deviate from non-relativistic calculations. In the high-frequency part of the
spectrum, we note appreciable deviations to the purely classical calculations
which may be linked to quantum averaging effects.Comment: 30 pages, 7 figure
PyFstat: a Python package for continuous gravitational-wave data analysis
Gravitational waves in the sensitivity band of ground-based detectors can be emitted by a number of astrophysical sources, including not only binary coalescences, but also individual spinning neutron stars. The most promising signals from such sources, although not yet detected, are long-lasting, quasi-monochromatic Continuous Waves (CWs). The PyFstat package provides tools to perform a range of CW data-analysis tasks. It revolves around the F-statistic, a matched-filter detection statistic for CW signals that has been one of the standard methods for LIGO-Virgo CW searches for two decades. PyFstat is built on top of established routines in LALSuite but through its more modern Python interface it enables a flexible approach to designing new search strategies. Hence, it serves a dual function of (i) making LALSuite CW functionality more easily accessible through a Python interface, thus facilitating the new user experience and, for developers, the exploratory implementation of novel methods; and (ii) providing a set of production-ready search classes for use cases not yet covered by LALSuite itself, most notably for MCMC-based followup of promising candidates from wide-parameter-space searches
Coherent storage and phase modulation of single hard x-ray photons using nuclear excitons
Coherent storage and phase modulation of x-ray single-photon wave packets in
resonant scattering of light off nuclei is investigated theoretically. We show
that by switching off and on again the magnetic field in the nuclear sample,
phase-sensitive storage of photons in the keV regime can be achieved.
Corresponding phase modulation of the stored photon can be accomplished
if the retrieving magnetic field is rotated by . The development
of such x-ray single-photon control techniques is a first step towards
forwarding quantum optics and quantum information to shorter wavelengths and
more compact photonic devices.Comment: 12 pages, 6 figures; v2 modified to match the published version,
condensed to 4 figures, results unchange
Interference in the resonance fluorescence of two incoherently coupled transitions
The fluorescence light emitted by a 4-level system in to
configuration driven by a monochromatic laser field and in an external magnetic
field is studied. We show that the spectrum of resonance fluorescence emitted
on the transitions shows a signature of spontaneously generated
interference effects. The degree of interference in the fluorescence spectrum
can be controlled by means of the external magnetic field, provided that the
Land\'e g-factors of the excited and the ground state doublet are different.
For a suitably chosen magnetic field strength, the relative weight of the
Rayleigh line can be completely suppressed, even for low intensities of the
coherent driving field. The incoherent fluorescence spectrum emitted on the
transitions exhibits a very narrow peak whose width and weight depends on
the magnetic field strength. We demonstrate that the spectrum of resonance
fluorescence emitted on the transitions show an indirect signature of
interference. A measurement of the relative peak heights in the spectrum from
the transitions allows to determine the branching ratio of the
spontaneous decay of each excited state into the channel
Ultrarelativistic Electron-Beam Polarization in Single-Shot Interaction with an Ultraintense Laser Pulse
Spin-polarization of an ultrarelativistic electron beam head-on colliding with an ultraintense laser pulse is investigated in the quantum radiation-reaction regime. We develop a Monte-Carlo method to model electron radiative spin effects in arbitrary electromagnetic fields by employing spin-resolved radiation probabilities in the local constant field approximation. Due to spin-dependent radiation reaction, the applied elliptically polarized laser pulse polarizes the initially unpolarized electron beam and splits it along the propagation direction into two oppositely transversely polarized parts with a splitting angle of about tens of milliradians. Thus, a dense electron beam with above 70\% polarization can be generated in tens of femtoseconds. The proposed method demonstrates a way for relativistic electron beam polarization with currently achievable laser facilities
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