Electrooptical studies of electrical discharges along a laser spark in air

A study is made of the dynamics of electrical breakdown in air along a laser spark of length $1$–$40$ cm acted on by a $600$ kV voltage pulse lasting $30$ nsec. It is found that a discharge develops in the form of ionizing waves which move in a stepwise fashion. After beginning at a velocity of $2$–$3 \cdot 10^9$ cm/sec, the wave front initially slows down and then the front velocity increases suddenly to $4$–$20 \cdot 10^9$ cm/sec When the electron density ahead of the wave was small the wave was observed to stop. The ionization wave was demonstrated to be stable in the optimum regimes. When a single laser ignition source is created in the gap, ionization waves develop on its surface and move in both directions. An electrical discharge with two independent trajectories is created. The helical instability is observed to develop in the discharge channel when the current flows for a long time. The electrical properties of the discharge channel along a discrete spark and of the channel of a continuous laser spark are studied.