Movie S1.

Direct observation of the reactive interface, shown in Fig. 3C. Each frame is the average of 10 images. Movie is a montage of approx. 25 min and runs at 5 fps. Contrast scale: −0.33 to +0.32. (Unless noted otherwise, scale bars in Movies S1–S5: 1 µm.) Movies S1–S5 frame rates are given in femtopicoseconds and compared with the real-time rate in hertz.