Dynamics of the detonation products of lead azide. IV. Laser shadowgraphy of expanding species

Laser resonant shadowgraphy (LRS) and laser nonresonant shadowgraphy (LNRS) are used to monitor the detonation products of lead azide. Photographs of the cloud of products are obtained via illumination with a doubled dye laser tuned on-resonance to the ³P₁^o-³P ₀ transition of the Pb atom at 283.31 nm, and off-resonance at 284.31 nm. The versatility of the diagnostics and its applicability to detonation products expanding into vacuum and into atmospheric pressure air are demonstrated. The LRS monitors the density gradients of both lead atoms and solid particles formed in the detonation, whereas the LNRS detects only the latter. Expansion into vacuum through a nozzle leads to an increase in the velocity (from ∼4.5 to ≳5 km/s) and density of the atoms and to a decrease in the density of the particles. The LRS measurements show that the expansion of both products in air is relatively slow (∼0.75 km/s) and leads to production of shock waves. From the shape of the shock waves created by an obstacle when the products expand into vacuum, the Mach number is estimated to be ≳20 in the outer parts and around 3 in the inner parts of the cloud.