Time-resolved pulsed-plasma characterization using broadband terahertz pulses correlated with fluorescence imaging

Near-monocycle terahertz (THz)-bandwidth electromagnetic pulses have been used to probe pulsed-discharge argon plasmas at various pressures from 10to50Torr. Time-resolved electric field measurements were made of the THz pulse with and without plasma allowing a full characterization of the real and imaginary parts of the plasma index of refraction. Electron densities ne⩾1013cm−3 and collision rates γp⩾1011s−1 were deduced by applying a simple Lorentz model to the measured time-domain pulse with no plasma and comparing it to the measured pulse with the plasma present. Minimizing the rms error between these in the two-dimensional parameter space (ne,γp) fixed the values for each point in time of the plasma evolution. Optical fluorescence imaged transverse to the THz beam path was used to estimate the density profile used in the propagation model.