Electron number density measurements using laser-induced breakdown spectroscopy of ionized nitrogen spectral lines

Abstract

Spectrally broadened, singly ionized nitrogen emission lines are monitored to determine electron number densities in laser-induced plasma from aluminum, nano- and bulk-zinc monoxide, as well as hydrogen-rich plastic and wood targets. The optical emission spectra for N II at the average wavelength of 500.33nm are recorded in standard ambient temperature and pressure environments. For time delays of 25 to 450ns from the onset of the 1064-nm Nd:YAG radiation induced optical breakdown, the electron number densities in the range of 5.1 ±1 ×1019 to 0.22 ±0.04 ×1019cm−3 are inferred from the continuum and the nitrogen spectral line analysis. In addition, the corresponding electron temperatures of 10.1 ±0.6eV to 1 ±0.2eV are determined from the calculated absolute spectral radiance values in the near infrared region. At the early stages of plasma emission, Balmer series hydrogen lines are embedded in free electron radiation yet the broadening of the N II lines yields reliable electron number density values.