Studies of detonations as a potential source for visible chemical lasers

For the past few years we have investigated the possibility of obtaining preferential population of specific electronic states of lead atoms following the detonation of lead azide (LA), Pb(N₃)₂ a well known primary explosive. This investigation is a part of an ongoing search in several laboratories for chemical lasers in the visible wavelength region. Our previous studies revealed that under suitable conditions enhanced emission in the Pb(³P₁ ⁰ →^ID₂) transition at 722.9 nm is obtained from the cloud of detonation products. However, it also was found that the cloud contains solid particles in addition to atomic and molecular species. The opacity caused by the particles is obviously undesirable in a medium where lasing is expected. In the present paper we report on controlling the population of excited species and of the size and density of the particles via expansion of the products through a nozzle. To visualize and characterize the products, we use emission spectroscopy, laser transmission spectroscopy, laser resonant shadowgraphy (LRS) and real time pressure measurements. The population of the excited states is deduced from the emission. From transmission measurements at 0.633, 0.67, 1.31 and 10.6 μm, the size of the particles, both under free expansion and through a nozzle, is evaluated to be around 0.9 and 0.6 jLi, respectively. From the LRS and pressure measurements the velocity and density distributions of the gaseous products and of the solid particles is inferred. It is shown that by utilizing a nozzle it is possible to obtain a transparent medium at the nozzle exit for a few microseconds. Progress in the efforts to achieve population inversion in the transparent medium is reported.