Threshold characteristics of collective optical breakdown in an aerosol medium

A threshold model is developed for a collective optical discharge induced in an aerosol medium as a result of interaction of plasma-vapor microjets formed at individual particles. It is shown that this discharge may be formed in several essentially different regimes, including collective heating, individual-collective heating, and burning. It is found that collective heating using fairly long pulses has the lowest intensity threshold for breakdown in the visible and near infrared. The proposed model is used to obtain an estimate of the breakdown threshold under collective heating conditions that agrees with known experimental data and those obtained by the present authors. The conditions for the establishment of individualcollective heating typical of Q-switched laser pulses in the far infrared are indicated. An analysis is made of the dependence of the collective breakdown threshold on the physicochemical properties of the aerosol material.