Aerosol clearing with a 10.6-um precursor pulse

The breakdown threshold for a 10.6-μm 200-ns laser pulse in air filled with carbon particles was increased by application of a low-intensity high-fluence precursor pulse, When the beam contained many particles with diameters
\leq4 \mu
m, the threshold was raised to within a factor of ≃3 of clean air with a 40-J/cm
²
precursor. With single 50-μm particles in the beam, the threshold was raised a factor of ≈19 which was within a factor of ≈2 of clean air, The mechanisms responsible for the particle clearing are shown to be the vaporization of small particles and the jetting of larger particles out of the beam. The coupling coefficient for carbon particles was found to be ≈2 dyn. s/J and the long-pulse breakdown threshold for 50-μm carbon particles was found to be
\approx2 \times 10^{7}
W/cm
²
, with times to breakdown ranging from 1 to 15 μs.