  Optimum design of efficient nanowire solar cells requires better
understanding of light diffusion in a nanowire array. Here we demonstrate that
our recently developed ultrafast all-optical shutter can be used to directly
measure the dwell time of light in a nanowire array. Our measurements on
disordered ZnO nanowire arrays, "nanowire forests," indicate that the photon
mean free path and the dwell time of light can be well predicted from SEM
images.
