Laser light scattering in a laser-induced argon plasma: Investigations of the shock wave

Abstract Shock wave produced by a laser induced spark in argon at atmospheric pressure was examined using Rayleigh and Thomson scattering. The spark was generated by focusing a laser pulse from the second harmonic ( λ  = 532 nm) of a nanosecond Nd:YAG laser using an 80 mm focal length lens, with a fluence of 2 kJ·cm − 2 . Images of the spark emission were recorded for times between 30 ns and 100 μs after the laser pulse in order to characterize its spatial evolution. The position of the shock wave at several instants of its evolution and for several plasma regions was determined from the Rayleigh-scattered light of another nanosecond Nd:YAG laser (532 nm, 40 J·cm − 2 fluence). Simultaneously, Thomson scattering technique was applied to determine the electron density and temperature in the hot plasma core. Attempts were made to describe the temporal evolution of the shock wave within a self-similar model, both by the simple Sedov–Taylor formula as well as its extension deduced by de Izarra. The temporal radial evolution of the shock position is similar to that obtained within theory taking into account the counter pressure of the ambient gas. Density profiles just behind the shock front are in qualitative agreement with those obtained by numerically solving the Euler equations for instantaneous explosion at a point with counter pressure.