title: Temperature dependent characterization of terahertz vibrations of explosives and related threat materials.
abstract: Waveguide terahertz time-domain spectroscopy (THz-TDS) is used to characterize the temperature dependent vibrational properties of three threat-related materials: 4-amino-dinitrotoluene (4A-DNT), pentaerythritol tetranitrate (PETN), and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX). These materials are characterized as thin polycrystalline layers deposited in the 50 micron gap of a metal parallel plate waveguide. For each material waveguide THz-TDS at least partially resolves the underlying vibrational spectrum and reveals new features that have not been observed in previous free space measurements of these materials. Strong experimental evidence for a phase transformation is observed for 4A-DNT as the polycrystalline layer on the waveguide surface is cooled to near 200 K. For PETN a highly resolved spectrum containing eleven vibrational lines is observed at 11 K with full-width at half maximum linewidths ranging from 7 GHz to 40 GHz. Based on comparison to measurements in the literature, our PETN measurement suggests that it is possible to produce narrow linewidths from a polycrystalline layer that approach those from a single crystal. Finally, for HMX, a highly resolved vibrational spectrum is measured that is assigned to the metastable gamma polymorph.
authors.affiliation: Naval Research Laboratory, Electronics Science and Technology Division, Washington, DC 20375, USA. joseph.melinger@nrl.navy.mil
authors.forename: Joseph S
authors.initials: JS
authors.lastname: Melinger
authors.forename: S Sree
authors.initials: SS
authors.lastname: Harsha
authors.forename: N
authors.initials: N
authors.lastname: Laman
authors.forename: D
authors.initials: D
authors.lastname: Grischkowsky
mesh_terms: D004867:Equipment Design; D019544:Equipment Failure Analysis; D053834:Explosive Agents / Q000032:analysis / Q000737:chemistry*; D008422:Materials Testing / Q000295:instrumentation*; D013696:Temperature; D055053:Terahertz Radiation; D055068:Terahertz Spectroscopy / Q000295:instrumentation*
chemical_list: D053834:Explosive Agents