Development of a compact terahertz time-domain spectrometer for the measurement of the optical properties of biological tissues.

Terahertz spectrometers and imaging systems are currently being evaluated as biomedical tools for skin burn assessment. These systems show promise, but due to their size and weight, they have restricted portability, and are impractical for military and battlefield settings where space is limited. In this study, we developed and tested the performance of a compact, light, and portable THz time-domain spectroscopy (THz-TDS) device. Optical properties were collected with this system from 0.1 to 1.6 THz for water, ethanol, and several ex vivo porcine tissues (muscle, adipose, skin). For all samples tested, we found that the index of refraction (n) decreases with frequency, while the absorption coefficient (µ(a)) increases with frequency. Muscle, adipose, and frozen/thawed skin samples exhibited comparable n values ranging between 2.5 and 2.0, whereas the n values for freshly harvested skin were roughly 40% lower. Additionally, we found that the freshly harvested samples exhibited higher µ(a) values than the frozen/thawed skin samples. Overall, for all liquids and tissues tested, we found that our system measured optical property values that were consistent with those reported in the literature. These results suggest that our compact THz spectrometer performed comparable to its larger counterparts, and therefore may be a useful and practical tool for skin health assessment.

Terahertz interferometric and synthetic aperture imaging.

The stand-off imaging properties of a terahertz (THz) interferometric array are examined. For this application, the imaged object is in the near-field region limit of the imaging array. In this region, spherical and circular array architectures can compensate for near-field distortions and increase the field of view and depth of focus. Imaging of THz point sources is emphasized to demonstrate the imaging method and to compare theoretical predictions to experimental performance.

Polarized light reflection from strained sinusoidal surfaces.

We propose optical polarization imaging as a minimally invasive technique for measuring the mechanical properties of plastics and soft tissues through their change in reflectance properties with applied strain or force. We suggest that changes in surface roughness are responsible for the linear reflectivity changes with applied stretch or strain. Several aspects of this model are tested, including the dependence on the angle of incidence, the change in scattering and absorption coefficients with strain, and the lateral spatial resolution. The application of the technique to multilayer structures such as skin and competing optical effects such as laser speckle are discussed.