(Color online) Sketch of microwave scattering from laser spark
(Color online) Relative electron number densities at avalanche breakdown, computed with Eqs. (4) and (5) The arrows show the time delays when the breakdown criterion (the dotted horizontal line) is realized.
(Color online) Experimental setup of microwave scattering from laser spark.
(Color online) Sample measurement signal of microwave scattering from a laser spark in room air. The inset window shows zoomed in view of the precursor pulse.
(Color online) Precursor part of microwave scattering signal at various locations around the laser breakdown region relative to the microwave induced polarization direction. The receiver angles are 0° [dashed dot dot (green) line], 45° [dashed (red) line], 90° [solid (black) line], and 135° [dotted (blue) line]. Each curve represents an average of 64 pulses. For all curves, .
(Color online) Short time (left) and long time (right) microwave scatterings at and at and 0°. Note that the precursor scattering is independent of , indicating scattering in the Rayleigh range, whereas the long time scattering is in the Mie regime.
(Color online) Dependence of peak microwave scattering signal on distance of the receiver. The (black) curve is a fit to the maximum scattering intensity at different distances. For comparison, (green) curve and (blue) curve are also shown in the figure.
(Color online) A zoomed precursor part of normalized microwave scattering signals at different laser pulse intensities. The arrows show the time moments when the accepted breakdown criterion (the horizontal line as in Fig. 2) is realized.
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