Paradox of small particles in the pulsed laser initiation of explosive decomposition of energetic materials

The dependences of the critical energy density required to initiate the explosive decomposition of lead azide and the radius of the most heated nanoparticle on the pulse duration of the first harmonic of neodymium laser (1064 nm) are calculated within the framework of the micro-hotspot model of thermal explosion. The calculations are carried out with account for the dependence of the absorption efficiency factor of the laser pulse on the lead nanoparticle radius. With the maximum value of the absorption efficiency factor (1.18), the lead nanoparticle radius (in lead azide) becomes 74 nm. If the pulse duration is short (smaller than 40 ns), the radius of the most heated lead nanoparticle in the lead azide matrix varies slightly (less than 15%) and equals 63.5 nm within the range of short pulse durations. Accounting for the dependence of the absorption efficiency factor of the laser pulse on the nanoparticle radius makes it possible to resolve the paradox of small particles.