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. We 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, we are 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 we use synchrotron radiation sources at Argonne Lab, Berkeley Lab, and elsewhere. Students in 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.