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Träfflista för sökning "L773:1094 4087 ;pers:(Ekeberg Tomas)"

Sökning: L773:1094 4087 > Ekeberg Tomas

  • Resultat 1-7 av 7
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1.
  • Andreasson, Jakob, et al. (författare)
  • Automated identification and classification of single particle serial femtosecond X-ray diffraction data
  • 2014
  • Ingår i: Optics Express. - 1094-4087. ; 22:3, s. 2497-2510
  • Tidskriftsartikel (refereegranskat)abstract
    • The first hard X-ray laser, the Linac Coherent Light Source (LCLS), produces 120 shots per second. Particles injected into the X-ray beam are hit randomly and in unknown orientations by the extremely intense X-ray pulses, where the femtosecond-duration X-ray pulses diffract from the sample before the particle structure is significantly changed even though the sample is ultimately destroyed by the deposited X-ray energy. Single particle X-ray diffraction experiments generate data at the FEL repetition rate, resulting in more than 400,000 detector readouts in an hour, the data stream during an experiment contains blank frames mixed with hits on single particles, clusters and contaminants. The diffraction signal is generally weak and it is superimposed on a low but continually fluctuating background signal, originating from photon noise in the beam line and electronic noise from the detector. Meanwhile, explosion of the sample creates fragments with a characteristic signature. Here, we describe methods based on rapid image analysis combined with ion Time-of-Flight (ToF) spectroscopy of the fragments to achieve an efficient, automated and unsupervised sorting of diffraction data. The studies described here form a basis for the development of real-time frame rejection methods, e. g. for the European XFEL, which is expected to produce 100 million pulses per hour. (C)2014 Optical Society of America
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2.
  • Loh, N. Duane, et al. (författare)
  • Sensing the wavefront of x-ray free-electron lasers using aerosol spheres
  • 2013
  • Ingår i: Optics Express. - 1094-4087. ; 21:10, s. 12385-12394
  • Tidskriftsartikel (refereegranskat)abstract
    • Characterizing intense, focused x-ray free electron laser (FEL) pulses is crucial for their use in diffractive imaging. We describe how the distribution of average phase tilts and intensities on hard x-ray pulses with peak intensities of 1021 W/m(2) can be retrieved from an ensemble of diffraction patterns produced by 70 nm-radius polystyrene spheres, in a manner that mimics wavefront sensors. Besides showing that an adaptive geometric correction may be necessary for diffraction data from randomly injected sample sources, our paper demonstrates the possibility of collecting statistics on structured pulses using only the diffraction patterns they generate and highlights the imperative to study its impact on single-particle diffractive imaging.
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3.
  • Martin, A. V., et al. (författare)
  • Noise-robust coherent diffractive imaging with a single diffraction pattern
  • 2012
  • Ingår i: Optics Express. - 1094-4087. ; 20:15, s. 16650-16661
  • Tidskriftsartikel (refereegranskat)abstract
    • The resolution of single-shot coherent diffractive imaging at X-ray free-electron laser facilities is limited by the low signal-to-noise level of diffraction data at high scattering angles. The iterative reconstruction methods, which phase a continuous diffraction pattern to produce an image, must be able to extract information from these weak signals to obtain the best quality images. Here we show how to modify iterative reconstruction methods to improve tolerance to noise. The method is demonstrated with the hybrid input-output method on both simulated data and single-shot diffraction patterns taken at the Linac Coherent Light Source. (C) 2012 Optical Society of America
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4.
  • Martin, A. V., et al. (författare)
  • The extraction of single-particle diffraction patterns from a multiple-particle diffraction pattern
  • 2013
  • Ingår i: Optics Express. - 1094-4087. ; 21:13, s. 15102-15112
  • Tidskriftsartikel (refereegranskat)abstract
    • The structures of biological molecules may soon be determined with X-ray free-electron lasers without crystallization by recording the coherent diffraction patterns of many identical copies of a molecule. Most analysis methods require a measurement of each molecule individually. However, current injection methods deliver particles to the X-ray beam stochastically and the maximum yield of single particle measurements is 37% at optimal concentration. The remaining 63% of pulses intercept no particles or multiple particles. We demonstrate that in the latter case single particle diffraction patterns can be extracted provided the particles are sufficiently separated. The technique has the potential to greatly increase the amount of data available for three-dimensional imaging of identical particles with X-ray lasers.
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5.
  • Park, Hyung Joo, et al. (författare)
  • Toward unsupervised single-shot diffractive imaging of heterogeneous particles using X-ray free-electron lasers
  • 2013
  • Ingår i: Optics Express. - 1094-4087. ; 21:23, s. 28729-28742
  • Tidskriftsartikel (refereegranskat)abstract
    • Single shot diffraction imaging experiments via X-ray free-electron lasers can generate as many as hundreds of thousands of diffraction patterns of scattering objects. Recovering the real space contrast of a scattering object from these patterns currently requires a reconstruction process with user guidance in a number of steps, introducing severe bottlenecks in data processing. We present a series of measures that replace user guidance with algorithms that reconstruct contrasts in an unsupervised fashion. We demonstrate the feasibility of automating the reconstruction process by generating hundreds of contrasts obtained from soot particle diffraction experiments.
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6.
  • Rath, Asawari D., et al. (författare)
  • Explosion dynamics of sucrose nanospheres monitored by time of flight spectrometry and coherent diffractive imaging at the split-and-delay beam line of the FLASH soft X-ray laser
  • 2014
  • Ingår i: Optics Express. - 1094-4087. ; 22:23, s. 28914-28925
  • Tidskriftsartikel (refereegranskat)abstract
    • We use a Mach-Zehnder type autocorrelator to split and delay XUV pulses from the FLASH soft X-ray laser for triggering and subsequently probing the explosion of aerosolised sugar balls. FLASH was running at 182 eV photon energy with pulses of 70 fs duration. The delay between the pump-probe pulses was varied between zero and 5 ps, and the pulses were focused to reach peak intensities above 1016 W/cm2 with an off-axis parabola. The direct pulse triggered the explosion of single aerosolised sucrose nano-particles, while the delayed pulse probed the exploding structure. The ejected ions were measured by ion time of flight spectrometry, and the particle sizes were measured by coherent diffractive imaging. The results show that sucrose particles of 560-1000 nm diameter retain their size for about 500 fs following the first exposure. Significant sample expansion happens between 500 fs and 1 ps. We present simulations to support these observations.
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7.
  • Yoon, Chun Hong, et al. (författare)
  • Unsupervised classification of single-particle X-ray diffraction snapshots by spectral clustering
  • 2011
  • Ingår i: Optics Express. - 1094-4087. ; 19:17, s. 16542-16549
  • Tidskriftsartikel (refereegranskat)abstract
    • Single-particle experiments using X-ray Free Electron Lasers produce more than 10(5) snapshots per hour, consisting of an admixture of blank shots (no particle intercepted), and exposures of one or more particles. Experimental data sets also often contain unintentional contamination with different species. We present an unsupervised method able to sort experimental snapshots without recourse to templates, specific noise models, or user-directed learning. The results show 90% agreement with manual classification.
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  • Resultat 1-7 av 7

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