Terahertz scattering and water absorption for porosimetry

Abstract

We use terahertz transmission through limestone sedimentary rock samples to assess the macro and micro porosity. We exploit the notable water absorption in the terahertz spectrum to interact with the pores that are two orders of magnitude smaller (<1μm) than the terahertz wavelength. Terahertz water sensitivity provides us with the dehydration profile of the rock samples. The results show that there is a linear correlation between such a profile and the ratio of micro to macro porosity of the rock. Furthermore, this study estimates the absolute value of total porosity based on optical diffusion theory. We compare our results with that of mercury injection capillary pressure as a benchmark to confirm our analytic framework. The porosimetry method presented here sets a foundation for a new generation of less invasive porosimetry methods with higher penetration depth based on lower frequency (f<10THz) scattering and absorption. The technique has applications in geological studies and in other industries without the need for hazardous mercury or ionizing radiation.

State-of-the-art in terahertz sensing for food and water security – A comprehensive review

“…Matthias C Hoffmann et al [5] generated the highest-energy ultrashort THz pulses by optical rectification of femtosecond pulses in LiNbO3 using the tilted-pulse-front pumping technique, which is inherently scalable to increase the available THz pulse energy and field strength. The THz radiation has many advantages over other imaging modalities in many aspects including non-ionizing [7], classifying species of tissue [8], and scattering and water absorption for porosimetry [9]. As a result, the terahertz radiation has shown widespread potential applications in diverse areas to address the real-world problems including genomics [10], medical diagnostics [11], pharmacology [12], healthcare applications [13] [14], Body-Area Networks (BAN) [15] [16], wireless communication [17] [18], environmental monitoring [19], agriculture [20] and food analysis [21] [22], defence and security [23]- [25].…”

Multi-Pass Free Electron Laser Assisted Spectral and Imaging Applications in the Terahertz/Far-IR Range Using the Future Superconducting Electron Source BriXSinO

“…THz spectroscopy in both frequency and time domain have been also applied for tracing gases. THz spectral signatures for example in hydrogen cyanide (HCN) [153,154], carbon monoxide (CO) [155,156], formaldehyde (H 2 CO) [157,158], and water (H 2 O) [159,160] allow to identify and quantify the individual gases from the pure rotational transitions.…”

“…Since THz waves are non-ionizing, they represent a suitable option for noninvasive spectroscopy, imaging [161,162] and insitu monitoring [163,164]. Since THz radiation is highly sensitive to polar molecules, it has been successfully used to determine the hydration levels in skin tissue [159], both in vitro and in-vivo [161,165], in order to discern between tumoral and healthy tissues for cancer diagnosis [166][167][168]. In many bio-applications, a key factor is that the THz radiation is strongly reflected by conductive materials and strongly absorbed by polar liquids, on the contrary the THz waves can penetrate a large number of organic or inorganic materials which are opaque in visible or IR ranges.…”

Measuring Open Porosity of Porous Materials Using THz-TDS and an Index-Matching Medium

“…The total porosity can thus be calculated from a THz-TDS measurement by utilizing effective medium theory and knowing the intrinsic refractive index of the solid matrix. This method has been demonstrated to measure the porosity of rocks [20] and pharmaceutical tablets [21][22][23] as well as to analyze the anisotropy of pore structures [18,24].…”