Journal
OPTICS EXPRESS
Volume 18, Issue 26, Pages 27238-27250Publisher
OPTICAL SOC AMER
DOI: 10.1364/OE.18.027238
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Funding
- Office of Naval Research
- Defense Threat Reduction Agency [10-2960M]
- Direct For Mathematical & Physical Scien
- Division Of Physics [0757680] Funding Source: National Science Foundation
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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. (C)2010 Optical Society of America
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