  Differential dynamic microscopy (DDM) is increasingly used in the fields of
soft matter physics and biophysics to extract the dynamics of microscopic
objects across a range of wavevectors using optical microscopy. Standard DDM is
limited to detecting dynamics no faster than the camera frame rate. We report
on an extension to DDM where we sequentially illuminate the sample with
spectrally-distinct light and image with a color camera. By pulsing blue and
then red light separated by a lag time much smaller than the camera's exposure
time we are able to use this two-color DDM method to measure dynamics occurring
much faster than the camera frame rate.
