Schlieren cinematographic and holographic diagnostic of a laser-produced plasma in xenon

Abstract

We have studied extensively a gas breakdown in xenon produced by a giant pulse ruby laser with a power <100 MW. Detailed information concerning the structure of the laser plasma formation and of the following expansion has been obtained by different optical methods, including schlieren techniques (single frames and ultra high speed cinematography) and holography. The high quality of the holographic pictures was achieved by the use of a monomode laser. With this we were able to visualize the plasma history and to determine the velocities of the boundary layer and of the blast wave with utmost accuracy. Investigations of the electron density and electron temperature showed that a relaxation time of about 10 nsec is necessary to establish local thermodynamic equilibrium states. After this relaxation time it is then possible to carry out thermodynamic calculations, applying the shock-wave theory, to relate the optically measured expansion velocity with the plasma parameters involved. The mean specific internal energy ∊¯, for instance, attained values in excess of 1012 erg/g which decayed rapidly during the first 100 nsec to about 5 · 1010 erg/g. By comparing the results to theoretical calculations of ∊¯ we obtained a first estimate of the temperature, taking into consideration the partial densities nj as well as the partition functions Zj(i) of the xenon atoms, the single-charged ions, and the double-charged ones. Furthermore, a two-step iteration computer program was used to give more detailed and more accurate results on the variations of the pressure, temperature, partial densities, and enthalpy as a function of time.