Influence of the size of inclusions of ultrafine nickel particles on the laser initiation threshold of PETN

We investigated the probability of explosion of tetranitropentaerythrite ($\rho$ = 1.73 g/cm$^3$) containing 0.1% (by weight) ultrafine nickel particles of size 270–300 and 140–175 nm at the distribution maxima depending on the energy density of the initiating laser pulse (1064 nm, 14 ns). In the first case, the critical energy density corresponding to a 50% the probability of explosion was 1.4 J/cm$^2$, and in the second case, 0.7 J/cm$^2$. Dependences of the light absorption cross section and the absorption coefficient on the inclusions particle size were calculated using the microhotspot theory of laser ignition. The calculation results are consistent with the microhotspot model of the initiation of thermal explosion.