Physics-based processing for terahertz reflection spectroscopy and imaging

The spectra obtained from Terahertz (THz) reflection imaging can be distorted by scattering from rough interfaces, layers, and granular inclusions. Since the facets of the object being imaged are not generally aligned normal to the THz beam, the received signal is produced from diffuse scattering, which can be appreciably lower in signal strength than specular returns. These challenges can be addressed with advanced signal processing approaches based upon the coherent and incoherent combination of returns from multiple sensors and frequencies. This paper presents two examples of physics-based processing strategies applied to THz imaging spectroscopy. The first method is based on synthetic aperture processing of a 2D sensor array to provide variable depth focused images of buried inclusions (a ball bearing embedded in polyethylene sample). The second method uses correlation processing to coherently combine multiple sensors and multiple frequencies to extract material signatures from measurements of THz scattering from rough interfaces. Results for both methods show an increase in performance relative to conventional imaging or spectroscopy approaches.