Terahertz Ellipsometry for Reflection-Mode Material Characterization

As technologies utilizing THz radiation (light) are developed, the optical properties for many materials need to be determined accurately as a function of frequency. In a security screening system, measured optical properties might be used to distinguish, independent of shape, between threat and background materials. Improved optical elements for increasingly advanced THz systems will require optical constants and instrumentation for design and quality control. Measured THz optical properties are intrinsically connected to underlying low-energy physical processes and thereby allow testing of existing scientific theories and exploration of novel developments such as artificially structured meta-materials. Ellipsometry is the preeminent technique for accurate, quantitative determination of complex-valued optical constants and for non-destructively characterizing layered structures. The J. A. Woollam Co. proposes developing a variable-angle spectroscopic ellipsometer for operation at terahertz (THz) frequencies as an addition to the company’s existing line of ellipsometers, which span frequencies from the infrared (IR-VASE®, 10 to 150 THz) to the vacuum ultraviolet (VASE® 150 to 2000 THz). Work by Drs. Mathias Schubert and Tino Hofmann at the University of Nebraska-Lincoln (UNL) in far-infrared and THz ellipsometry using frequency-domain techniques shows promise. In collaboration with UNL, phase I would evaluate potential system components (sources, detector, polarization-state control optics) for use in a commercial THz ellipsometer.