Bernal Institute Research Forum

Date: 17th September 2018 to 17th September 2018
Time: 12:00 to 13:00
Duration: One hour
Location: MSG-025 MSSI Building Extension

Professor Chris Jacobsen, Northwestern University, USA.

X-ray Microscopy: Going Smaller and Larger.

X-ray sources have had brightness increases at a rate faster than Moore’s law for computing, and nanofocusing optics have seen great improvements too. This has allowed us to obtain 18 nm resolution images of whole, frozen hydrated eukaryotic cells along with 80 nm resolution images of trace metal distributions, and micrometer resolution images of mesoscale neuroanatomy in whole mouse brains. As one tries to combine higher resolution (going smaller) with bigger objects (whole mouse brains), imaging beyond the depth of field needs to be considered. A path is presented towards meeting this challenge, using classical multislice wave propagation methods with modern numerical optimization approaches.

Professor Chris Jacobsen’s research is focused on developing new methods in x-ray microscopy, and applying them to interesting problems in biology, environmental science, and materials science. Using either diffractive optics (like Fresnel zone plates fabricated using electron beam lithography), or lens-less methods where iterative phase retrieval methods are used to reconstruct an image from a coherent diffraction pattern, images with a spatial resolution of 20 nm or better can be obtained. In absorption contrast, one can combine imaging with spectroscopy to study chemical speciation at the nanoscale, or one can use fluorescence detection to study trace element distributions with parts-per-billion sensitivity. Professor Jacobsen and his research group are also developing detectors and image reconstruction algorithms that can be used to obtain quantitative phase contrast images with hard X-rays, and thus put elemental distributions into their ultrastructural context and also go from measurements of content to measurements of concentration (since concentration gradients drive chemical processes). Finally, the group is interested in understanding the limitations that radiation damage presents to x-ray microscopy studies, and in developing both cryo-instrumentation and sample preparation methods to mitigate those limitations. These efforts require bright x-ray beams, so synchrotron radiation sources at Argonne Lab, Berkeley Lab, and elsewhere are used. The group explore interesting problems in optical physics and in instrumentation, and get to broaden their perspective by working with collaborators from other research fields like biology, environmental science, and materials science.

Awards and Honors of Professor Jacobsen: Residential Faculty Fellow (White House/NSF), 1992-1997; International Dennis Gabor Award (Hungary), 1996; Kurt Heinrich Award (Microbeam Analysis Society), 2001; R&D 100 award winner, 1999; Argonne Distinguished Fellow, 2016. Fellow, Optical Society of America (1999), American Association for the Advancement of Science (2002), American Physical Society (2011).

Tea/coffee will be available at 11h45.

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