  We report observations of nanosecond nanometer scale heterogeneous dynamics
in a free flowing colloidal jet revealed by ultrafast x-ray speckle visibility
spectroscopy. The nanosecond double-bunch mode of the Linac Coherent Light
Source free electron laser enabled the production of pairs of femtosecond
coherent hard x-ray pulses. By exploring the anisotropic summed speckle
visibility which relates to the correlation functions, we are able to evaluate
not only the average particle flow rate in a colloidal nanoparticle jet, but
also the heterogeneous flow field within. The reported methodology presented
here establishes the foundation for the study of nano- and atomic-scale
heterogeneous fluctuations in complex matter using x-ray free electron laser
sources.
