  The behavior of silver and lead azides (scaly and threadlike crystals, and
compacted powders) in initiation of explosive decomposition by laser pulsed
radiation has been investigated. Initiation energy thresholds in irradiation at
wavelengths of 1064 nm, 532 nm, 354.7 nm, 266 nm corresponding to four laser
radiation harmonics have been measured. Samples both uncovered and covered with
a transparent dielectric (a quartz plate) with the compressive force of up to
0.5GPa were initiated. In the transparent spectral region (the first and second
laser harmonics) of the heavy metal azide matrix the effect of covering the
sample surface with a plate on initiation energy threshold was insignificant,
whereas, in the region of bandgap absorption (the fourth harmonic) strong
dependence of the initiation threshold on whether the surface under irradiation
is uncovered or covered. The results obtained have been considered with the
account of the influence of the transparent plate on gas-dynamic unloading of
the thermal site, which is formed in the bandgap absorption of laser radiation
in a thin near-surface layer.
