X-ray imaging is a broad term which includes a number of techniques, ranging from raster scanning to full-field using attenuation, scattering or X-ray emission as contrast mechanism. Lately the real breakthroughs happened in terms of improvements in the temporal resolution of all these diverse techniques. With the new generation of X-ray sources (diffraction limited storage rings such as MAX IV and X-ray free electron lasers) it is likely that this trend will continue shedding light to nature’s ultra-fast phenomena at the micrometer scale and beyond [1].
In the last 15 years of tomographic microscopy at synchrotrons we experienced in average an order of magnitude improvement in the acquisition speed every three years [2]. While in the early times the scan time of 60 minutes at 1-3 μm voxel size was the state-of-the-art, today we can achieve a temporal resolution of 20 ms. Which are the main scientific drivers for this development? What technical and conceptual breakthroughs contributed to such a spectacular improvements? Are we at the technical or physical limits of the spatio-temporal resolution? What will the future of diffraction limited light sources bring? These will be some of the questions I will reflect on in my lecture and indicate some new directions in multimodal and multiscale imaging using advanced X-ray optics [3]
The standard imaging instruments at synchrotron beamlines perform very well down to about one micrometer spatial resolution. Breaking the one micrometer resolution barrier is conceived typically by transforming the nearly-parallel synchrotron beam to divergent beam to achieve magnification in the X-ray regime. At XFEL sources it is still not obvious which imaging modality is best suited to achieve spatial resolution in the range of some tens of nanometers. At this scale the organelles in cells can be viewed. Are such studies feasible at all? To shed some light onto this I will review the performence of different nanoimaging modalities in terms of sensitivity, dose efficiency, spatio- temporal resolution, requirements on the sample preparation and availability at synchrotron sources [4].
2. R. Mokso, F. Marone, S. C. Irvine, M. Nyvlt, D. Schwyn, K. Mader, G. K. Taylor, H. G. Krapp, M. Skeren, M. Stampanoni, Advantages of phase retrieval for fast tomogrpahy, J. Phys. D. 46, (2013), 494004.
4. P. Villanueva-Perez, B. Pedrini, R. Mokso, M. Guizar-Sicairos, F. Arcadu, M. Stampanoni, Signal-to-noise criterion for free-propagation imaging tech- niques at free-electron lasers and synchrotrons. Optics Express, 24(4), (2016), 3189– 3201.
The acknowledgement goes to the TOMCAT team at the Swiss Light Source of the Paul Scherrer Institut for their involvement in most of the studies to be presented in this lecture.