Fourier-transform far-infrared spectroscopic ellipsometry for standoff material identification

✍ Scribed by Michele Ortolani; Ulrich Schade

• Publisher: Elsevier Science
• Year: 2010
• Tongue: English
• Weight: 374 KB
• Volume: 623
• Category: Article
• ISSN: 0168-9002
• DOI: 10.1016/j.nima.2010.02.079

✦ Synopsis

The ellipsometry is an efficient method to determine the optical properties of matter. It has been largely employed with grating spectrometers in the visible, UV and near-infrared ranges for the characterization of thin films, surfaces and interfaces. In the mid-and far-infrared, where most substance-specific absorption lines are present, spectroscopic ellipsometry with Fourier-transform spectrometers is still not extended as a routine method. In particular, the lack of powerful sources in the far-infrared/ terahertz range has prevented standoff application of this method. We will show that it is possible to measure the complex dielectric constant of a solid in the far-infrared and terahertz range by a reflection experiment with polarized light and ellipsometric analysis with a suitable calibration procedure. Extraction of terahertz synchrotron radiation from storage rings provides a suitable source for researchgrade experiments. The optical constants determined by ellipsometry compare well with those obtained by Kramers-Kronig procedures, a method which, however, requires broader frequency range and absolute reflectance standard. We will present the case of remote spectroscopic identification of explosive materials, which is relevant for forthcoming security applications.