Plume dynamics of laser produced air plasma

Dynamical evolution of air spark (plume) created using ns and ps laser pulses is investigated. Two dimensional temporal evolution images of the spark are recorded using intensified CCD orthogonal to the laser propagation direction. Optical emission spectroscopy is used to determine temperature and density of plasma. Assuming local thermodynamic equilibrium of plasma electron temperature ~ 1.1 eV and an electron density ~ 1. 73 × 1018 cm-3at the 210 mJ energy and vibrational temperature of N2+ ~ 0.45 eV is determined. The dependence of the electron density on the laser energy and delay time after the initiation of the spark is discussed. To study the plasma channel by hydrodynamic evolution of air spark in the laser focus, an experiment using pump probe configuration is done. An increase in the length by a factor of ~3 and increase in electron density by a factor of 1.5 was observed at 7 ns delay of the nanosecond pulse relative to the picoseconds laser pulse. An extensive investigation of channel formation will be discussed.