Mathematical simulation of the spectrum of a nonequilibrium laser plasma

A method is proposed for calculating the spectrum of a nonequilibrium plasma, which is based on a nonequilibrium collision–radiation model including all common line broadening mechanisms (natural, pressure, Doppler, and quadratic Stark effect broadening) and supplemented with the energy balance equations for electrons and ions. The nonequilibrium populations of the ground and excited states of neutral atoms and ions for an arbitrary instant of time are found by solving kinetic equations. The shape of each spectral line is determined by its central core calculated in the collision approximation up to the frequency boundary of its applicability, where the central core is 'joined' with the line wings calculated in the quasi-static approximation. The validity of this theoretical model is confirmed by simulations of a number of experimental studies of emission spectra under the conditions of a local thermodynamic equilibrium. It is shown that the calculated and experimental data obtained for the ground-state lines of the first carbon ion and neutral helium and argon atoms are in good agreement. The nonequilibrium spectrum of the optical breakdown in argon is calculated. Mathematical simulations showed that the intensities of nonequilibrium line spectra can be noticeably (by several times) lower than those of equilibrium spectra.