In order to advance XFEL-based SPI to the resolution level required to solve the structure of biological macromolecules, a great variety of experimental and algorithmic challenges have to be overcome, such as sample injection, experimental background minimization, identification of hits, orientation determination, and density reconstruction [2]. Despite many recent advances, an experimental demonstration for orientation determination of SPI data in the very relevant weak scattering limit (< 100 scattered photons per pattern) is still outstanding.

We report here on an experiment at ESRF’s beamline ID10 during which a small (<1 µm) lithographically produced particle has been illuminated with a coherent synchrotron beam. This way, hundreds of thousands of very weak diffraction patterns in hundreds of particle orientations have been collected.

We will show how these data, without explicit knowledge of the individual frame orientations and with on the order of 100 photons per pattern, can be used to reconstruct a 3D diffraction volume in Fourier space using the Expansion-Maximization-Compression algorithm [3]. This diffraction volume is then used to reconstruct the real-space density of the particle by conventional iterative phase retrieval.

References

[1] A. Barty, J. Küpper, H.N. Chapman, Ann. Rev. Phys. Chem. 64, 415 (2013).

[2] A. Aquila et al., Struct. Dyn. 2, 041701 (2015).

[3] N.D. Loh, V. Elser, Phys. Rev. E 80, 026705 (2009).

Contact : oier.bikondoa@esrf.fr