Theoretical calculations are described to investigate the behavior of solid explosive when heated by continuous and pulsed laser. A one-dimensional model is proposed and the numerical solutions have been obtained for the time-dependent nonlinear heat equation with the appropriate initial and boundary conditions. Relationships between various ignition parameters are analyzed and possible ignition mechanisms are discussed. Theoretical calculations are applied to the primary solid explosive b lead azide. It has been argued that the initiation of b lead azide with low energy laser is thermal in origin.