  Filamentation due to the growth of a Weibel-type instability was observed in
the interaction of a pair of counter-streaming, ablatively-driven plasma flows,
in a supersonic, collisionless regime relevant to astrophysical collisionless
shocks. The flows were created by irradiating a pair of opposing plastic (CH)
foils with 1.8 kJ, 2-ns laser pulses on the OMEGA EP laser system. Ultrafast
laser-driven proton radiography was used to image the Weibel-generated
electromagnetic fields. The experimental observations are in good agreement
with the analytical theory of the Weibel instability and with particle-in-cell
simulations.
