The existence of characteristic internal scales for the duration of any physical phenomenon imparts a special significance to investigations of the effect of temporal factors on the process under study. Unavoidably reflected in the relationships found, this circumstance aids both in the identification of, and in the deeper understanding of the mechanisms for the phenomenon. This work was undertaken to specify the assumptions used in modeling the laser initiation of explosives resulting from the appearance of a thermal instability in the neighborhood of an absorbing microinhomogeneity of submicron size R /sub o/ . The fundamental characteristics of the heating centers are evaluated on the basis of an experimental study of the dependence of the threshold energy for initiation of lead azide on the duration of the exciting pulse.