Research Projects

Ptychography: a new X-ray diffractive imaging technique 

X-rays have very short wavelengths which makes them suitable to image samples at very high resolution. The difficulty with doing an X-ray microscope is that the diffractive index of most material is very close to 1 at the X-ray wavelengths which makes it impossible to have a conventional lens for X-rays. Instead zone plates are used, but the precision to which we can manufacture zone plates limits the maximum resolution possible. 

Ptychography is a new X-ray diffractive imaging technique which makes it possible to obtain very high resolution images of various samples, fundamentally only limited by the wavelength of the X-rays used.

It works by illuminating a sample with a focused beam of X-rays on overlapping regions and recording the resulting diffraction patterns. The patterns are then used as input for a reconstruction algorithm that recovers an image of the sample. This bypasses the need for a lens, replacing it instead with an algorithm.

Diagram of a ptychography experiment. The experiment is similar to a scanning transmission X-ray microscope, but while in the latter only the transmitted intensity is used to generate an image, in ptychography the entire scattering pattern is used, resulting in a higher resolution image.

I am developing the software that will power the new COSMIC beamline at the Advanced Light Source, which will do the reconstruction of the sample images from the diffraction patterns in real time, providing the same kind of feedback that users expect from the conventional microscope.

Large-scale geophysical electromagnetic imaging and modeling on graphical processing units

I am adapting krylov solvers used in geophysical applications for graphical processing units (GPUs) so that existing codes can take advantage of the processing power that GPUs provide.

Relative performance of the QMR algorithm on the GPU and 2 CPU implementations. The GPU is a Tesla C2050 and the CPUs are 8 core Intel Nehalems.