Speaker
Christian Gutt
(University Siegen)
Description
X-ray radiation damage provides a serious bottle neck for investigating μs to s dynamics on nanometer length scales employing X-ray photon correlation spectroscopy. This limitation hinders the investigation of real time dynamics in most soft matter and biological materials which can tolerate only X-ray doses of kGy and below. Here, we show that this bottleneck can be overcome by low dose serial X-ray speckle visibility spectroscopy. The concept consists in spreading the dose needed for a correlation function over the entire sample volume by measuring at every spot on the sample the visibility of a speckle pattern as a function of exposure time. Mitigating the absorbed dose in this way is done at the expense of signal strength; the collected speckle patterns are sparse containing signal strength of 10-2 photons per pixel and possibly even less. We show that the speckle visibility correlation function can nevertheless be extracted by proper assignment of photon probabilities using a sufficiently large number of images. Employing X-ray doses of 640 Gy to 8.5 kGy and analyzing the sparse speckle patternswe follow as an example the slow nanoscale dynamics of an ionic liquid (IL) at the glass transition. Our method is especially relevant for the upcoming diffractiom limited storage rings providing a two orders of magnitude increase in coherent X-ray flux.
Primary author
Christian Gutt
(University Siegen)
