Sub-picosecond Laser-Driven Shocks in Metals and Energetic Materials

Abstract

Abstract.A high-energy sub-picosecond laser was used both to drive a shock into thin film targets and to spectroscopically interrogate the shocked material. Targets were thin films of molecular materials coated or grown upon thin vapor-plated metal films on thin glass substrates, or neat metal films on thin glass substrates. The non-linear optical interaction of the shock-driving laser with the thin glass substrate produced surprisingly flat shock waves. Sub-picosecond time-resolved frequency-and spatial-domain interferometries were used to characterize the shock wave as it transited from the thin metal film into the thin molecular material layer. Overviews of the effect of the pressure-dependent complex index of refraction of the shocked thin film metal layer, ultrafast interferometric interrogation of shocked molecular materials (examples: glycidyl azide polymer and nitrocellulose thin films), and progress in preparation of, as well as the need for, uniform, well oriented, thin energetic material layers appropriate to such highly time-resolved methods are presented.

Benchtop Energetics: Research Progress, Concept Evaluation, and Apparatus Development

“…In fact, a secondary technical objective of this program is to "enable high-throughput bench-scale testing and evaluation of candidate advanced nanometric energetic materials, including those available only in sub-gram quantities." We will not attempt to duplicate Prof. Dlott's, or others' [65][66][67], ongoing condensed phase ultrafast laser spectroscopic studies; rather we will add the novel element of utilizing shock target arrays in vacuum, combined with nanosecond resolution spectroscopic diagnostics to follow the subsequent exothermic chemical reaction kinetics.…”

“…The availability of a second tunable nanosecond laser system will enable considerably more powerful spectroscopic diagnostics for characterizing both the shock initiation conditions and the gas phase reaction kinetics. While (sub)picosecond resolution is required for properly characterizing the time dependence of condensed phase shock-induced processes on the molecular length scale [54][55][56][57][58][59][60][61][62][63][65][66][67], nanosecond lasers have recently been used to measure shock pressures in laser-driven 80-µm-thick Teflon films via spontaneous Raman spectroscopy [70][71][72]. We are also anxious to apply gas-phase laser induced fluorescence and transient absorption diagnostics that can probe for non-emitting molecular species, which could represent the majority of the material in the reacting flow [73].…”

“…As discussed above in the Proposal, our experimental approach can be seen as a milligram and microsecond extension of prior thin-film ultrafast-laser-driven energetic materials experiments [54][55][56][57][58][59][60][61][62][63][64][65][66][67] --enabled by a sample-in-vacuum configuration. We seek to characterize the molecular debris emerging from these small-scale energetic events for further clues on the progress of the chemical reaction kinetics.…”