Grain size dependent scattering studies of common materials using THz time domain techniques

In recent times, the far infrared or the terahertz (1 THz = 10 ¹² cycles/sec and 300 μm in wavelength) region of electromagnetic spectrum has become a promising radiation for spectroscopic identification of different types of biomaterials. The present work investigates the effect of grain size on the THz spectra of chalk, salt, sugar and flour using THz time-domain spectroscopy. It has been observed that at lower frequencies, solids of small grain sizes of non absorbing materials show rising trends in their extinction spectra. Here, we obtain extinction spectra of granular salt, chalk, sugar and flour between 0.2 to 1.2 THz and show that the experimentally obtained extinction can be predicted on the basis of the Mie Scattering model for small grain sizes. The current study is an attempt to understand the absorption spectrum of a few such materials having no significant intrinsic absorption in the THz region by separating the independent contributions of true absorption of the material and scattering losses due to its morphology in the extinction of the material. This might open up the possibility of distinguishing these materials of known grain sizes based on their rising trend of the extinction spectra at lower frequencies.