On the radiative heat loss and axis-switching phenomena of a decaying laser spark

Abstract

A three-dimensional numerical simulation of a decaying laser spark in gaseous nitrogen has been carried out in Cartesian co-ordinate. The simulation starts with the introduction of a laser pulse in the domain. Thermal equilibrium has been assumed throughout the numerical simulation involving the species N2, N, N+, e−. The boundary conditions are treated following characteristic property of the waves to ensure smooth transmission of the blast wave out of the computational domain. The previously unexplained axis-switching phenomenon of the breakdown region has been explained, and a qualitative comparison of the same with experimental schlieren images has been made. The total radiation loss, including the loss during the breakdown, has been calculated. The variation of inverse Bremsstrahlung radiation, black body radiation, and spectral radiation of atomic nitrogen with time have been shown separately. Additionally, the temporal variation of radiation intensity of atomic nitrogen over a wavelength range has been plotted. The total radiation loss has been found to be small compared to the deposited laser energy.