Abstract
A series of photographs for a streamer propagation process in water was successfully observed using a nano-pulse discharge system, an ultra high speed camera system with a microscope lens and a phase shift type Mach-Zehnder interferometer. After the initiation process of 600 ns - 800 ns from the applying voltage of 16 kV_<0p> - 17.5 kV_<0p>, a primary streamer occurred. It accompanied with a shock wave and the period of the propagation was several hundred ns. The propagation velocity of the primary streamer was around 1.5 km/s.
