Stereo-photography of streamers in air

Standard photographs of streamer discharges show a two-dimensional projection. Here, we present stereophotographic images that resolve their three-dimensional structure. We describe the stereoscopic setup and evaluation, and we present results for positive streamer discharges in air at 0.2–1bar in a point-plane geometry with a gap distance of 14cm and a voltage pulse of 47kV. In this case, an approximately Gaussian distribution of branching angles of 43°±12° is found; these angles do not significantly depend on the distance from the needle or on the gas pressure.