  Terahertz (THz) tomography is a rather novel technique for nondestructive
testing that is particularly suited for the testing of plastics and ceramics.
Previous publications showed a large variety of conventional algorithms adapted
from computed tomography or ultrasound tomography which were directly applied
to THz tomography. Conventional algorithms neglect the specific nature of THz
radiation, i.e. refraction at interfaces, reflection losses and the beam
profile (Gaussian beam), which results in poor reconstructions. The aim is the
efficient reconstruction of the complex refractive index, since it indicates
inhomogeneities in the material. A hybrid algorithm has been developed based on
the algebraic reconstruction technique (ART). ART is adapted by including
refraction (Snell's law) and reflection losses (Fresnel equations). Our method
uses a priori information about the interface and layer geometry of the sample.
This results in the 'Modified ART for THz tomography', which reconstructs
simultaneously the complex refractive index from transmission coefficient and
travel time measurements.

Numerical Analysis