A Fast NIR Spectrometer for Examining Explosive Events: Emission of PETN Based Explosives and H\u3csub\u3e2\u3c/sub\u3eO Absorption Method Feasibility

The chemical dynamics and decomposition pathways of explosive materials are not entirely known. Measurements of chemical transients during explosive events can lead to enhanced knowledge of the detailed chemistry and eventually control of the end products; however, these measurements are often difficult to obtain due to fast time scales and harsh environments. Optical diagnostics present fast-response, minimally invasive methods for resolving properties in detonation environments and previous fast spectroscopic measurements have been recorded in the ultra-violet and visible regions. This work extends the range of such measurements to the near-infrared (NIR) through the development of a fiber-coupled NIR spectrometer utilizing a fast InGaAs array. The characteristics and applications of this spectrometer are investigated through temporally and spectrally resolved measurements during the detonation and post-detonation combustion in arena-type explosives experiments. The spectrometer was used to examine the emission features and temperatures of atomic and molecular species with microsecond time resolution from pure pentaerythritol tetranitrate (PETN) charges and PETN charges doped with 10% (by mass) Ag and Al microparticles. The post-detonation spectra were observed between 750 nm and 1500 nm at rates up to 46k-spectra/sec, and key features were identified. Emission spectra from the particle doped charges followed a Planckian distribution at later times (\u3e40μs) and spectral pyrometry temperature measurements were determined from the spectra. The NIR spectrometer can also be used to acquire absorption spectra which can allow for the measurement of bulk gas temperature and direct species concentrations as well as provide more control over the probed volume. An investigation was conducted on the feasibility of using the newly developed NIR spectrometer in explosives experiments to measure water absorption in the 1330-1380 nm region and determine temperatures and concentrations of H2O using a fiber coupled broad light source. The fiber size, resolution, and path-length necessary for accurate temperature mol fraction H2O measurements were determined