Jeffrey Kallman (15-ERD-028)
Imaging with scanning coherent diffraction ("ptychography"), a form of microscopy recently made practical by new computational algorithms, is useful when it is difficult to make an effective lens for the electron or x-ray probe and when it is desired to image both phase and attenuation. The data used to form images is collected by acquiring diffraction patterns from overlapping regions on the subject. We plan to accelerate the reconstruction of ptychographic data, which is an iterative process and for which a number of techniques have evolved. Ptychography could be a powerful tool for nondestructive characterization using optical, x-ray, or particle-based imaging, with potential uses from biological imaging to chip assurance. We plan to develop and implement two acceleration techniques. We will build a state-of-the-art reconstruction code suite and an optical data-acquisition system, acquire data, and reconstruct it. Once the code suite is validated, we will incorporate the acceleration techniques into our code suite.
If successful, we expect to develop a state-of-the-art ptychographic reconstruction code suite with acceleration techniques that should reduce the time required for reconstruction by a factor of between two and ten (depending on the methods used). We will also develop the capability for a flexible optical ptychography data-acquisition system using a microscope with a motorized XY stage (horizontal and vertical axes) and an integrated camera and laser light source. Using this system, we will prepare microscope slides of single- and multiple-layer subjects and acquire test ptychographic data. With this project, we will gain experience in the use of ptychography for computer chip assurance. There is also the potential for creating new intellectual property on the acceleration techniques we develop.
Our proposed capability in new nondestructive characterization is rooted in the Laboratory's core competency of high-performance computing, simulation, and data science to evaluate the performance of existing systems for which physical testing is extremely limited.
FY15 Accomplishments and Results
In FY15 we (1) implemented the three two-dimensional reconstruction techniques we want to accelerate (shown in figure), (2) built a software infrastructure into which we can incorporate the two acceleration techniques, and (3) implemented the optical test bed.
Ptychography is an imaging technique used with coherent radiation for which it is difficult to make lenses (such as for x-ray probes). It can image both the phase and attenuation by scanning the specimen with overlapping beams and reconstructing the resultant diffraction patterns computationally. We showed that two reconstruction acceleration techniques were feasible. The image shows a simulated data acquisition situation and reconstructions with and without the acceleration techniques. The differences between reconstructions are imperceptible.