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Schematics of plasma characterization using THz-wave-enhanced fluorescence. IF, interference filter. PMT, photomultiplier.
The pressure dependences of the enhanced fluorescence in (a) pure nitrogen gas (b) mixture of nitrogen and helium gas. The laser pulse energy is . (c) The comparison between measured (solid squares) and calculated (dash line) relaxation time.
(a) The measured (symbol) and fitted (line) at 100, 300, and 500 Torr, respectively. All the curves are normalized for clarity. (b) The plasma densities extracted from curves, are compared with background fluorescence signal (without THz field) at different pressures. Background fluorescence signal was normalized to plasma density data.
(a) The measured nitrogen fluorescence with different excitation laser pulse energies at 65 Torr. The shade area is enlarged for clarity. (b) Measured electron relaxation time. Inset, the measured background fluorescence signal (sold red circle) and calculated ion density being normalized to fluorescence signal (blue dash line).
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