Contactless Transient THz Temperature Imaging by Thermo-transmittance Technique on Semi-transparent Materials

THz waves have shown to be effective for several applications, such as security, non-destructive testing, and water content monitoring for porous materials and food products. This study aims to highlight the use of THz radiation to measure temperature variations of thin insulating materials opaque in the visible or IR range (PVC, PTFE, PMMA, and wood) by using a spectral thermo-transmittance technique. THz wave optical transmittance in materials show high sensitivity to temperature variations. The goal of this paper is to demonstrate the transient temperature gradient dependence of THz transmitted signals inside materials to develop a new contactless method for measuring temperature of thin materials semi-transparent to THz radiation. The principle is based on synchronous detection, using an infrared camera coupled with a THz to infrared thermal converter (TTC) with modulated millimeter-scale waves (2.7 mm). The results show a correlation between the transient temperature and the optical transmittance coefficient. Several types of samples semi-transparent to THz radiation are tested, and the corresponding thermo-transmittance coefficients as reported for PVC, PTFE, PMMA, and wood are respectively 0.805, 0.395, 0.640, and 1.177 K^?1 m^?1.