Laser-Induced Fluorescence of Xe i and Xe II in Ambipolar Plasma Flow

Laser-induced fluorescence diagnostic technique is applied here to probe xenon neutrals and single-charged ions in an ambipolar plasma source. A single tunable diode laser is employed for pumping both following transitions: 6s ²[1/2]₁ ⁰ - 6p ²[3/2]₁ ⁰ (centered at 834.68 nm; air) and 5d[4]_7/2 - 6p[3]_5/2 (centered at 834.72 nm; air), for Xe I and Xe II detection, respectively. The corresponding decay states are 6s[3/2]₁ ⁰ and 6s[2]_3/2 leading to fluorescence signal at 473.415 and 541.915 nm, respectively. A detailed description of the experimental setup along with time-averaged fluorescence signals are presented, demonstrating the possible application of the above adjacent pumping wavelengths in xenon ambipolar plasmas for probing both ions and neutrals under various operating conditions. A comprehensible discussion to what extent the registered laser-induced fluorescence signals mirror velocity distribution functions is realized, following hyperfine splitting and isotopic shift analysis.