Abstract
We propose the application of a terahertz electromagnetic pulse (THz pulse) for non-contact measurement of local water content in the skin. The free-space propagating THz pulse is generated as dipole radiation from a photoconductive antenna triggered by a femtosecond pulsed light from a mode-locked Ti: Sapphire laser. Strong interaction of the electromagnetic wave with water in the THz region enables the measurement of water content in the skin using the THz pulse. The ultrashort temporal width of the THz pulse can probe depth information on the skin in the same manner as the ultrasound pulse echo method. In this paper, we demonstrate measurements of water content and thickness of the analytical region in a human skin sample based on the time-of-flight method for THz pulse echo. A relative change of water content in the sample was determined by the change in the peak height of the THz pulse echoed from the skin surface. With respect to tomographic information on the skin, we observed THz pulse echo from an air-corneum interface and that from an epidermis-dermis interface, successively. Simultaneous quantification of the water content and thickness will be a powerful tool for monitoring the hydration level with respect to morphology of the skin.
