Effects of Anisotropic Excitation in Laser-Induced Fluoresceruce Spectroscopy (LIFS)

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Abstract
Various features of the effect of alignment in the upper-level population on the observed emission-line intensity, i.e., the spatially-anisotropic intensity distribution and polarization, are demonstrated using laser-induced fluorescence spectroscopy on the neon 2p 53s-2p 53p transitions in a plasma. Disalignment by atomic collision is observed on the 2p 2 level, and its rate coefficient is determined as (1.70 ±0.03) ×10-10 cm3s-1. The case of hyperfine-structure lines is discussed. Polarization is observed in the hydrogen Balmer α line fluorescence following the laser excitation of the same transition. Conditions are given under which the alignment effect is eliminated or can be neglected. Cases of unpolarized-light excitation and high-intensity excitation are discussed.