Effect of shockwave-induced density jump on laser plasma interactions in low-pressure ambient air

The dynamics of laser-produced plasma (LPP) and its shockwave-induced density jump (SIDJ) were investigated in low-pressure ambient air during the laser pulse using an optical interferometer. A tiny SIDJ could be observed clearly in ambient air with pressure as low as 3 Torr even during the rising edge of a 7 ns laser pulse. It was shown that the density jump and ionization could seed laser-induced ambient air breakdown at a relatively low pressure, which could significantly reduce laser energy deposited in the LPP. The ionization of the density jump was confirmed by dynamic emission imaging.