Hydrodynamic confirmation of quasi-similarity theory and its application to weak blast wave motion generated by ultrashort pulse laser breakdown in quiescent air

Abstract

The dynamics of the blast waves generated by ultrashort pulse laser breakdown can provide information on the energy and the dynamics of both the breakdown region and the laser pulse which created it. For conditions relevant to femtosecond laser breakdown in air, we show that the evolution of the blast waves can be described by quasi-similarity theory. By analyzing the motion of these weak blast waves, we calculate the energy deposited into the gas during the laser breakdown process. This technique can be applied to any set of blast waves where the back pressure cannot be neglected, and the blast waves propagate with an initial Mach number between 2 and 1.15. We calculate a non-dimensional curve describing the blast wave position in time which depends solely on the deposited energy and the ambient density using similarity parameters and multiple fluid dynamic simulations. The deposited energy can then be calculated by fitting experimental data to this generalized curve. This procedure is applied to two sets of experimental data and it is found that the calculated amounts of deposited energy agree with literature values. In addition, a very simple and novel Flux Corrected Transport (FCT) procedure is applied to the fluid solver to extend Boris and Books 1D algorithm to multiple dimensions.