Differences in the excitation of non-energetic and energetic residues with a 900 mJ, 6 ns
laser pulse (1064 nm) have been investigated. Emission from the
laser-induced plasma of energetic materials (e.g. triaminotrinitrobenzene [TATB],
cyclotrimethylene trinitramine [
RDX], and hexanitrohexaazaisowurtzitane [CL-20]) is significantly reduced compared to non-energetic materials (e.g.
sugar,
melamine, and
l-glutamine). Expansion of the resulting
laser-induced
shock wave into the air above the sample surface was imaged on a microsecond timescale with a high-speed camera recording multiple frames from each
laser shot; the excitation of energetic materials produces larger heat-affected zones in the surrounding atmosphere (facilitating deflagration of particles ejected from the sample surface), results in the formation of additional
shock fronts, and generates faster external
shock front velocities (>750 m s(-1)) compared to non-energetic materials (550-600 m s(-1)). Non-
explosive materials that undergo exothermic chemical reactions in air at high temperatures such as
ammonium nitrate and
magnesium sulfate produce
shock velocities which exceed those of the inert materials but are less than those generated by the exothermic reactions of
explosive materials (650-700 m s(-1)). The most powerful
explosives produced the highest
shock velocities. A comparison to several existing
shock models demonstrated that no single model describes the
shock propagation for both non-energetic and energetic materials. The influence of the exothermic chemical reactions initiated by the
pulsed laser on the velocity of the
laser-induced
shock waves has thus been demonstrated for the first time.