Temporal and spatial evolutions of plasma produced in a nanosecond laser field characterized by langmuir probe diagnostics

Based on the temporal and spatial evolutions of the plasma plume, the behaviour of the laser-produced plasma is studied using a wire Langmuir probe. The plasma is generated by focusing a Nd:YAG laser pulse of 30 ns pulse duration, similar to 110 mJ energy, and 1064 nm wavelength) on a solid metal (steel-316) target. By conducting experiments at low pressures (1 x 10(3)-5 x 10(-5) mbar), the following results were obtained: (a) At a lower pressure, the rise time of the electron signals is reduced, but the current amplitude is increased for both ions and electrons. (b) Fitting the shock wave model of propagation to the experimental results of the plasma plume expansion within the range 1-7 mm distance from the target shows better agreement at lower pressures. (c) For both electrons and ions, the velocity of the particles exhibited plume splitting (two regimes of velocities, namely fast and slow), which is interpreted as being dominant due to the ambipolar field. In addition, at the centimetre-scale distance from the target and using the time-of-flight method, the electron and ion velocities were determined to be similar to 3 x 10(7) and similar to 1.2 x 10(6) cm/s, respectively. The electron temperature is in the range 2-29 eV, and the ion density is in the range 10(11)-10(13) cm(-3) at milimeter to centimetre distances from the target.