Detection of a human hair with polaization-dependent THz-time domain spectroscopy

Terahertz spectroscopy of human hair has attracted much interest in fields such as biochemistry of biopolymer fiber, nondestructive food inspection, and monitoring health condition. We have measured human hairs by two orthogonal polarization directions with transmission terahertz time-domain spectroscopy (THz-TDS) in 0.2 to 3 THz band, and detected a difference between spectra of the two polarizations. The spectra also display the existence of specific spectral bands to identify human hairs. Particularly, we have demonstrated that it is possible to detect even one hair by this method.