Coherent microwave scattering

For plasmas with sufficiently low skin-depths, the target is periodically polarized in a uniform fashion, and the scattered field can be measured and analyzed.

Notable advantages of the technique include a high sensitivity, ease of calibration using a dielectric scattering sample,[2] good temporal resolution, low shot noise, non-intrusive probing, species-selectivity when coupled with resonance-enhanced multiphoton ionization (REMPI), single-shot acquisition, and the capability of time-gating due to continuous scanning.

[3] Initially devised by Mikhail Shneider and Richard Miles at Princeton University,[1] coherent microwave scattering has become a valuable technique in applications ranging from photoionization and electron-loss rate measurements[2][4][5][6][7][8] to trace species detection,[9] gaseous mixture and reaction characterization,[10][11][12] molecular spectroscopy,[13] electron propulsion device characterization,[14] standoff measurement of electron collision frequencies for momentum transfer through the scattered phase,[14] and standoff measurement of local vector magnetic fields through magnetically-induced depolarization.

[3] The Thomson regime refers to free plasma electrons oscillating in-phase with the incident microwave field.

Finally, the Rayleigh scattering regime can be observed which is associated with restoring-force-dominated electron motion and shares a ω4 dependence with its volumetric polarizability optical counterpart.