Aerosol-induced laser breakdown thresholds: effect of resonant particles

Laser intensity thresholds for the onset of stimulated Raman scattering and the breakdown in resonant micro-meter-sized droplets are reduced to below those for nonresonant droplets by a factor of ~ 3. This reduction is most likely caused by the enhancement of electromagnetic energy (photon) densities within the droplets over and above that in nonresonant droplets. The magnitude of the threshold reduction for breakdown is consistent with the assertion that (1) input (pump) wavelength resonances that initiate plasma have cavity Q's of ~ 10(4) and (2) finite regions of high-electromagnetic-energy density within the droplet, with dimensions of the order of the Debye length, are required to initiate plasma.