The Christiansen effect in terahertz time-domain spectra of coarse-grained powders

Spectral distortions are commonly observed in terahertz transmission spectra of ground substances immersed in a transparent host medium. This effect originates from scattering due to the index contrast between the grains and diluent. A phenomenological expression quantitatively accounts for the scattering induced attenuation and the phase delay experienced by the electric field transmitted through the sample. Based on the knowledge of the refractive indices of the sample and the host material, we present a procedure to eliminate the scattering contribution from the absorption spectra.