Weitz developed a new light scattering technique which they call dynamic speckle holography (DSH). Developed by postdoctoral fellow Stefano Aime, DSH creates an image of a speckle pattern of light scattered by a sample. The speckles are then analyzed to determine the time scale of their temporal correlations, providing an image of time scales across the sample. This can be used to measure the motion of the sample. In the figure on the right, the sample is fluid flowing in a channel. However, DSH can also be used to measure the strain field in a sample undergoing fracture. The power of DSH is that it relies on interference effects to sense the motion, and these are much more sensitive than other methods which inevitably entail measuring the motion of a scattering object. This makes DSH much more sensitive to motion and breaks the usual relationship between sensitivity and resolution. Weitz and Spaepen are applying DSH to investigate fracture phenomena.
Frans Spaepen (Material Science) and David A. Weitz (Physics & Applied Physics)
2020-2021 Harvard MRSEC (DMR-1420570)