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: $6s{~}^{\mathrm {2}} {[{1/2}]}_{\mathrm {1}}^{\mathrm {0}}$ – $6p{~}^{2} {[{3/2}]}_{\mathrm {1}}^{\mathrm {0}}$ (centered at 834.68 nm; air) and $5d{\mathrm {[{4}]}}_{\mathrm {7/2}}$ – $6p{\mathrm {[{3}]}}_{\mathrm {5/2}}$ (centered at 834.72 nm; air), for Xe I and Xe II detection, respectively. The corresponding decay states are $6s{\mathrm {[{3/2}]}}_{\mathrm {1}}^{\mathrm {0}}$ and $6s{\mathrm {[{2}]}}_{\mathrm {3/2}}$ 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.