Ultraviolet Laser-induced ignition of RDX single crystal
The RDX single crystals are ignited by ultraviolet laser (355 nm, 6.4 ns) pulses. The laser-induced damage morphology consisted of two distinct regions: a core region of layered fracture and a peripheral region of stripped material surrounding the core. As laser fluence increases, the area of the whole crack region increases all the way, while both the area and depth of the core region increase firstly, and then stay stable over the laser fluence of 12 J/cm2. The experimental details indicate the dynamics during laser ignition process. Plasma fireball of high temperature and pressure occurs firstly, followed by the micro-explosions on the (210) surface, and finally shock waves propagate through the materials to further strip materials outside and yield in-depth cracks in larger surrounding region. The plasma fireball evolves from isotropic to anisotropic under higher laser fluence resulting in the damage expansion only in lateral direction while maintaining the fixed depth. The primary insights into the interaction dynamics between laser and energetic materials can help developing the superior laser ignition technique.
Quantitative correlation between facets defects of RDX crystals and their laser sensitivity.
In this work, the {210} facets of cyclotrimethylenetrinitramine (RDX) single crystals with different quality were studied by scanning electron microscopy and atomic force microscopy. Their laser sensitivity was then assessed using a direct laser ignition test irradiated with ultraviolet laser (wavelength: 355nm, pulse width: 6.4ns). Quantitative relationships between laser sensitivity and surface defects of RDX (210) and (2¯1¯0) facets were investigated. It is determined that the laser sensitivity exhibits significant correlation with the surface roughness, size of which is comparable with scales of laser wavelength. 3D FDTD simulations disclose that this relationship can be well explained with light intensity modulation effects induced by micro-defects on the initial plane wave.
On the initiation of chemical reactions by electronic excitations in molecular solids

Abstract.In this article we briefly review the results of theoretical simulations for the initiation of chemistry processes in high-explosive crystals from a solid-state-physics viewpoint. We analyze the possibility of initiation of chemical reactions from excited electronic states. In other words, we look for conditions that facilitate electronic excitations in the crystal. Specifically, we describe modifications to the electronic structure of RDX (cyclotrimethylene trinitramine) induced by lattice defects and by a shock wave traversing the solid. Our approach is based on ab initio Hartree–Fock band-structure calculations with electronic correlation corrections. An excitonic mechanism and a hole model, suggested earlier, are discussed in connection with the most recent experimental and theoretical advances in ultrafast optical techniques. We also consider here possible new avenues in the development of detonation theory.