Photo- and thermochemical initiation of PETN under laser excitation

A method for separate control of the efficiencies of the photochemical and thermochemical mechanisms of initiation of energetic materials by laser excitation for a combined action of these mechanisms is proposed. The method is based on the difference in the timescales of the relevant photo- and thermochemical initiation processes, a factor that leads to a different dependence of the efficiencies of these mechanisms on the initiating pulse duration and initiation irradiance. An experimental validation of the method for the initiation of PETN with 1064- and 1070-nm light at irradiances of ∼109 and ∼104 W/cm2, respectively, is performed. The results show that, for the initiation of pure PETN at an irradiance of 109 W/cm2, the photochemical mechanism dominates, ensuring an initiation threshold of ∼4 J/cm2. In the case of samples with light-absorbing inclusions (carbon) and the same irradiance ∼104 W/cm2, only the thermochemical mechanism is operative, with an initiation threshold of ∼15 J/cm2. In the absence of light-absorbing inclusions, the sample does not explode even at a fluence of ∼75 J/cm2; i.e., in this case, the initiation threshold is clearly higher than this value.