Laser initiation of RDX crystal slice under ultraviolet and near-infrared irradiations

Abstract

Interactions between energetic materials and laser beams of specific frequency are of both scientific and engineering importance for understanding and manipulating the laser-induced ignition of energetic crystals. In this work, we investigate the effects of laser irradiation of variable energy densities from ultraviolet (355 nm) to near-infrared (1064 nm) on the ignition properties of a well-treated cyclotrimethylenetrinitramine (RDX) crystal slice (9.3 mm × 9.1 mm × 2.9 mm). The laser-induced damage and initiation dynamics were characterized in detail by using optical microscopy as well as an ultrafast pump-probe imaging technique at nanoseconds. It discloses that both ignition probabilities (p) of 355 and 1064 nm change exponentially with increasing laser fluence (H, J/cm2): p(355)=1−e−1.72*(H−3.981), p(1064)=1−e−0.74*(H−7.898). RDX crystals can be more easily ignited under ultraviolet laser irradiation than by near-infrared one due to its different absorptions (α(355) = 1.6306 cm−1, and α(1064) = 0.5313 cm−1) and the effects of photochemical initiation mechanism. The damage induced by either 355 nm or 1064 nm laser exhibits three typical morphologies varied with laser exposure. In addition, damage generated by ultraviolet laser appears on the incident surface of the crystal slice, while it is mainly located on the exit surface when being ignited by near-infrared laser. Our work sheds light on the dedicated interaction mechanism between energetic crystals and laser beams of various frequency and energy density.