Dynamic observation of a thermally activated structure change in 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) by second harmonic generation

Using optical second harmonic generation (SHG) we observe, for the first ti me, a structural change in the energetic material (dry-aminated production grade) TATB (1,3,5-triamino-2,4,6-trinitrobenzene) upon heating. This struc ture change is verified by X-ray powder diffraction (XPD). The kinetics of this structure change are measured and are found to closely match commonly accepted thermal decomposition parameters for the first step, analogous to observations made for the beta to delta phase transition in HMX (octahydro- 1,3,5,7-tetranitro-1,3,5,7-tetrazocine). Consequently, these solid structur e transitions appear to be coupled to the chemical decomposition mechanism or it may be the first physical process occurring. We apply this technique as a diagnostic to an ignition experiment. This experiment demonstrates tha t the structure change can be rapid (it is thermally activated) and that SH G can be used to indicate not only the solid structure change (large increa se in SHG intensity) but also the onset to significant decomposition (subse quent drop in SHG intensity). The ability to selectively change the efficie ncy of the SHG, in a single piece of explosive, is also demonstrated and ma y have novel nonlinear optical applications. This application of SHG to TAT E constitutes a fundamentally new probe in the dynamics of TATE decompositi on, ignition, and combustion and may have application to optical integrated devices for frequency conversion and information encoding.