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- Caleman, Carl, et al.
(author)
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Modeling of XFEL induced ionization and atomic displacement in protein nanocrystals
- 2012
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In: Proceedings of SPIE. - : SPIE. - 9780819492210 ; , s. 85040H-
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Conference paper (peer-reviewed)abstract
- X-ray free-electron lasers enable high-resolution imaging of biological materials by using short enough pulses to outrun many of the effects of radiation damage. Experiments conducted at the LCLS have obtained diffraction data from single particles and protein nanocrystals at doses to the sample over 3 GGy. The details of the interaction of the X-ray FEL pulse with the sample determine the limits of this new paradigm for imaging. Recent studies suggest that in the case of crystalline samples, such as protein nanocrystals, the atomic displacements and loss of bound electrons in the crystal (due to the high X- ray intensity) has the effect of gating the diffraction signal, and hence making the experiment less radiation sensitive. Only the incident photon intensity in the first part of the pulse, before the Bragg diffraction has died out, is relevant to acquiring signal and the rest of the pulse will mainly contribute to a diffuse background. In this work we use a plasma based non-local thermodynamic equilibrium code to explore the displacement and the ionization of a protein nanocrystal at various X-ray wavelengths and intensities.
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2. |
- Duane Loh, N., et al.
(author)
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Profiling structured beams using injected aerosols
- 2012
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In: Proceedings of SPIE. - : SPIE. - 9780819492210 ; , s. 850403-
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Conference paper (peer-reviewed)abstract
- Profiling structured beams produced by X-ray free-electron lasers (FELs) is crucial to both maximizing signal intensity for weakly scattering targets and interpreting their scattering patterns. Earlier ablative imprint studies describe how to infer the X-ray beam profile from the damage that an attenuated beam inflicts on a substrate. However, the beams in-situ profile is not directly accessible with imprint studies because the damage profile could be different from the actual beam profile. On the other hand, although a Shack-Hartmann sensor is capable of in-situ profiling, its lenses may be quickly damaged at the intense focus of hard X-ray FEL beams. We describe a new approach that probes the in-situ morphology of the intense FEL focus. By studying the translations in diffraction patterns from an ensemble of randomly injected sub-micron latex spheres, we were able to determine the non-Gaussian nature of the intense FEL beam at the Linac Coherent Light Source (SLAC National Laboratory) near the FEL focus. We discuss an experimental application of such a beam-profiling technique, and the limitations we need to overcome before it can be widely applied.
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