44 research outputs found
Time dependence of Bragg forward scattering and self-seeding of hard x-ray free-electron lasers
Free-electron lasers (FELs) can now generate temporally short, high power
x-ray pulses of unprecedented brightness, even though their longitudinal
coherence is relatively poor. The longitudinal coherence can be potentially
improved by employing narrow bandwidth x-ray crystal optics, in which case one
must also understand how the crystal affects the field profile in time and
space. We frame the dynamical theory of x-ray diffraction as a set of coupled
waves in order to derive analytic expressions for the spatiotemporal response
of Bragg scattering from temporally short incident pulses. We compute the
profiles of both the reflected and forward scattered x-ray pulses, showing that
the time delay of the wave is linked to its transverse spatial shift
through the simple relationship , where
is the grazing angle of incidence to the diffracting planes. Finally,
we apply our findings to obtain an analytic description of Bragg forward
scattering relevant to monochromatically seed hard x-ray FELs.Comment: 11 pages, 6 figure
Single-Photon Entanglement in the keV Regime via Coherent Control of Nuclear Forward Scattering
Generation of single-photon entanglement is discussed in nuclear forward
scattering. Using successive switchings of the direction of the nuclear
hyperfine magnetic field, the coherent scattering of photons on nuclei is
controlled such that two signal pulses are generated out of one initial pump
pulse. The two time-resolved correlated signal pulses have different
polarizations and energy in the keV regime. Spatial separation of the entangled
field modes and extraction of the signal from the background can be achieved
with the help of state-of-the-art x-ray polarizers and piezoelectric fast
steering mirrors.Comment: minor changes, updated to the final version; 4 pages, 2 figure
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
Charge excitations associated with charge stripe order in the 214-type nickelate and superconducting cuprate
Charge excitations were studied for stipe-ordered 214 compounds,
LaSrNiO and 1/8-doped La(Ba, Sr)CuO
using resonant inelastic x-ray scattering in hard x-ray regime. We have
observed charge excitations at the energy transfer of 1 eV with the momentum
transfer corresponding to the charge stripe spatial period both for the
diagonal (nikelate) and parallel (cuprates) stripes. These new excitations can
be interpreted as a collective stripe excitation or charge excitonic mode to a
stripe-related in-gap state.Comment: 5 pages, 4 figure
Nuclear forward scattering in particulate matter: dependence of lineshape on particle size distribution
In synchrotron Moessbauer spectroscopy, the nuclear exciton polariton
manifests itself in the lineshape of the spectra of nuclear forward scattering
(NFS) Fourier-transformed from time domain to frequency domain. This lineshape
is generally described by the convolution of two intensity factors. One of them
is Lorentzian related to free decay. We derived the expressions for the second
factor related to Frenkel exciton polariton effects at propagation of
synchrotron radiation in Moessbauer media. Parameters of this Frenkelian shape
depend on the spatial configuration of Moessbauer media. In a layer of uniform
thickness, this factor is found to be a simple hypergeometric function. Next,
we consider the particles spread over a 2D surface or diluted in non-Moessbauer
media to exclude an overlap of ray shadows by different particles. Deconvolving
the purely polaritonic component of linewidths is suggested as a simple
procedure sharpening the experimental NFS spectra in frequency domain. The
lineshapes in these sharpened spectra are theoretically expressed via the
parameters of the particle size distributions (PSD). Then, these parameters are
determined through least-squares fitting of the line shapes.Comment: 13 pages, 12 figure