Experimental stark broadening parameters of Bi I, Bi II and Bi III spectral lines in laser-induced plasma

Abstract

We present experimentally determined Stark width parameters (w - Full Width at Half Maximum) for 5 neutral (Bi I), 13 singly (Bi II), and 3 doubly ionized (Bi III) bismuth atoms spectral lines in the wavelength range of 298 to 570 nm. The experiment was conducted with a Laser-Induced Plasma (LIP) in helium gas at reduced pressure, as a source of spectra recorded in side-on geometry. Plasma parameters were estimated after applying the inverse Abel transform to the laterally resolved LIP profiles. The widths and relative intensities of all selected bismuth spectral lines were determined by their fit to the Voigt function. Electron number density values, on different plasma radial positions, were estimated in the range of (0.3–1.1) × 10²³ m⁻³ based on the Stark broadening of the well-established diagnostic He I 587.56 nm spectral line. The electron temperature was determined using the Saha-Boltzmann method. Bismuth spectral lines were used to construct a Saha-Boltzmann plot for three consecutive ionization states of bismuth atoms, assuming Local Thermodynamic Equilibrium (LTE) in the LIP. These methods for determining electron number density and electron temperature enabled precise estimation of plasma parameters, and therefore also supported the accurate determination of the newly measured Stark width values of bismuth spectral lines. The experimental measurements in this study provided the first-ever data on Stark widths for selected specific bismuth spectral lines, not previously available according to the NIST database, which are suitable for further plasma diagnostics, astrophysical modeling, and the development of spectroscopic techniques in laboratory and industrial applications. We also discussed a well-known feature of bismuth, the hyperfine structure of spectral lines due to nuclear spin and associated magnetic moment.