Visualization of corona discharge induced by UV (248 nm) pulses of a KrF excimer laser

A KrF excimer laser (248 nm) was used to induce DC corona discharge streamers in air between the electrodes of a needle-to-plane geometry. The UV laser beam pulses were transformed into the form of a laser sheet (1.5 mm-thick and 20 mm-wide) that was positioned along the axis directed from the needle electrode to the plane electrode. The laser pulses were time-synchronized with the exposure of an ICCD camera that recorded images of the corona streamers induced by the laser sheet. The laser pulse energy flux (75 MW/cm(2)) crossing the gap was high enough to induce corona streamers with a reliability of 100 % even at relatively low operating voltages (e.g., 15 kV) at which self-sustained streamers could not occur. Due to the full synchronization of the corona streamer onset, induced by the laser pulse and the exposure of the ICCD camera, 2-D visualization of the corona streamer evolution with a time resolution of 10 ns was possible. The recorded images made possible determining such features of the corona discharge streamer as its velocity (2.5.10(5) m/s) and the diameters of the leader channel (200 mum) and leader streamers (100 mum).