598 research outputs found
Continuous Diffraction of Molecules and Disordered Molecular Crystals
The diffraction pattern of a single non-periodic compact object, such as a
molecule, is continuous and is proportional to the square modulus of the
Fourier transform of that object. When arrayed in a crystal, the coherent sum
of the continuous diffracted wave-fields from all objects gives rise to strong
Bragg peaks that modulate the single-object transform. Wilson statistics
describe the distribution of continuous diffraction intensities to the same
extent that they apply to Bragg diffraction. The continuous diffraction
obtained from translationally-disordered molecular crystals consists of the
incoherent sum of the wave-fields from the individual rigid units (such as
molecules) in the crystal, which is proportional to the incoherent sum of the
diffraction from the rigid units in each of their crystallographic
orientations. This sum over orientations modifies the statistics in a similar
way that crystal twinning modifies the distribution of Bragg intensities. These
statistics are applied to determine parameters of continuous diffraction such
as its scaling, the beam coherence, and the number of independent wave-fields
or object orientations contributing. Continuous diffraction is generally much
weaker than Bragg diffraction and may be accompanied by a background that far
exceeds the strength of the signal. Instead of just relying upon the smallest
measured intensities to guide the subtraction of the background it is shown how
all measured values can be utilised to estimate the background, noise, and
signal, by employing a modified "noisy Wilson" distribution that explicitly
includes the background. Parameters relating to the background and signal
quantities can be estimated from the moments of the measured intensities. The
analysis method is demonstrated on previously-published continuous diffraction
data measured from imperfect crystals of photosystem II.Comment: 34 pages, 11 figures, 2 appendice
Avalanche boron fusion by laser picosecond block ignition with magnetic trapping for clean and economic reactor
After the very long consideration of the ideal energy source by fusion of the
protons of light hydrogen with the boron isotope 11 (boron fusion HB11) the
very first two independent measurements of very high reaction gains by lasers
basically opens a fundamental breakthrough. The non-thermal plasma block
ignition with extremely high power laser pulses above petawatt of picosecond
duration in combination with up to ten kilotesla magnetic fields for trapping
has to be combined to use the measured high gains as proof of an avalanche
reaction for an environmentally clean, low cost and lasting energy source as
potential option against global warming. The unique HB11 avalanche reaction is
are now based on elastic collisions of helium nuclei (alpha particles) limited
only to a reactor for controlled fusion energy during a very short time within
a very small volume.Comment: 11 pages, 6 figures, Submitted to Proceedings 2nd Symposium High
Power Laser Science and Engineering, 14-18 MARCH 2016, Suzhou/Chin
Progress in Three-Dimensional Coherent X-Ray Diffraction Imaging
The Fourier inversion of phased coherent diffraction patterns offers images
without the resolution and depth-of-focus limitations of lens-based tomographic
systems. We report on our recent experimental images inverted using recent
developments in phase retrieval algorithms, and summarize efforts that led to
these accomplishments. These include ab-initio reconstruction of a
two-dimensional test pattern, infinite depth of focus image of a thick object,
and its high-resolution (~10 nm resolution) three-dimensional image.
Developments on the structural imaging of low density aerogel samples are
discussed.Comment: 5 pages, X-Ray Microscopy 2005, Himeji, Japa
Split-aperture laser pulse compressor design tolerant to alignment and line-density differences
This paper was published in Optics Letters and is made available as an electronic reprint with the permission of OSA. The paper can be found at the following URL on the OSA website: http://dx.doi.org/10.1364/OL.33.001902 Systematic or multiple reproduction or distribution to multiple locations via electronic or other means is prohibited and is subject to penalties under law
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Ultrahigh-intensity laser: physics of the extreme on a tabletop
This paper reviews the development of ultrahigh-intensity laser technology from the early 1960`s to the present, explaining the obstacles to each increase in intensity and the technical means used to overcome them. These included the shortening of pulses, mode locking, and chirped pulse amplification (CPA). The particular technical advances that make CPA possible included the invention of matched pulse stretchers and compressors and the development of ultrabroadband gain media. The paper then discusses the generation of ultrashort pulses and their characteristics. It then moves on to the Petawatt laser, which incorporates the CPA technology. It then addresses the question of whether it is possible to forecast the ultimate peak power that can be achieved by a laser system of a given size. Applications of ultrahigh-intensity lasers in different physical regimes are discussed
Three-dimensional coherent X-ray diffraction imaging of a ceramic nanofoam: determination of structural deformation mechanisms
Ultra-low density polymers, metals, and ceramic nanofoams are valued for
their high strength-to-weight ratio, high surface area and insulating
properties ascribed to their structural geometry. We obtain the labrynthine
internal structure of a tantalum oxide nanofoam by X-ray diffractive imaging.
Finite element analysis from the structure reveals mechanical properties
consistent with bulk samples and with a diffusion limited cluster aggregation
model, while excess mass on the nodes discounts the dangling fragments
hypothesis of percolation theory.Comment: 8 pages, 5 figures, 30 reference
Cryptotomography: reconstructing 3D Fourier intensities from randomly oriented single-shot diffraction patterns
We reconstructed the 3D Fourier intensity distribution of mono-disperse
prolate nano-particles using single-shot 2D coherent diffraction patterns
collected at DESY's FLASH facility when a bright, coherent, ultrafast X-ray
pulse intercepted individual particles of random, unmeasured orientations. This
first experimental demonstration of cryptotomography extended the
Expansion-Maximization-Compression (EMC) framework to accommodate unmeasured
fluctuations in photon fluence and loss of data due to saturation or background
scatter. This work is an important step towards realizing single-shot
diffraction imaging of single biomolecules.Comment: 4 pages, 4 figure
Femtosecond x-ray diffraction from an aerosolized beam of protein nanocrystals
We demonstrate near-atomic-resolution Bragg diffraction from aerosolized
single granulovirus crystals using an x-ray free-electron laser. The form of
the aerosol injector is nearly identical to conventional liquid-microjet
nozzles, but the x-ray-scattering background is reduced by several orders of
magnitude by the use of helium carrier gas rather than liquid. This approach
provides a route to study the weak diffuse or lattice-transform signal arising
from small crystals. The high speed of the particles is particularly well
suited to upcoming MHz-repetition-rate x-ray free-electron lasers
Exact field ionization rates in the barrier suppression-regime from numerical TDSE calculations
Numerically determined ionization rates for the field ionization of atomic
hydrogen in strong and short laser pulses are presented. The laser pulse
intensity reaches the so-called "barrier suppression ionization" regime where
field ionization occurs within a few half laser cycles. Comparison of our
numerical results with analytical theories frequently used shows poor
agreement. An empirical formula for the "barrier suppression ionization"-rate
is presented. This rate reproduces very well the course of the numerically
determined ground state populations for laser pulses with different length,
shape, amplitude, and frequency.
Number(s): 32.80.RmComment: Enlarged and newly revised version, 22 pages (REVTeX) + 8 figures in
ps-format, submitted for publication to Physical Review A, WWW:
http://www.physik.tu-darmstadt.de/tqe
Pulse compression and beam focusing with segmented diffraction gratings in a high-power chirped-pulse amplification glass laser system
This paper was published in Optics Letters and is made available as an electronic reprint with the permission of OSA. The paper can be found at the following URL on the OSA website: http://dx.doi.org/10.1364/OL.35.001783 Systematic or multiple reproduction or distribution to multiple locations via electronic or other means is prohibited and is subject to penalties under law
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