Introduction

Abstract

The generation and detection of terahertz (THz) frequency electromagnetic radiation and the study of materials interaction occurring in this frequency regime has been of considerable interest to the scientific community of late. The term terahertz is typically used to indicate the region of electromagnetic spectrum between the frequencies 100 GHz (100 × 10⁹ Hz) and 10 THz (10 × 10¹² Hz) corresponding to the sub-millimeter wavelength range 3 mm to 30 μm between the microwave and the infra-red bands. Terahertz radiation is often commonly referred to as T-rays or simply abbreviated as THz. Much of the scientific interest in T-rays is due to the unique properties of this type of radiation. Unlike X-rays, THz waves have very low photon energy and thus cannot lead to harmful photoionization in biological samples. THz waves are also transparent to most dry dielectric materials like wood, paper, cloth, and plastic and as such suffer less scattering than visible and IR waves due to their longer wavelengths. Furthermore, many biological and chemical compounds exhibit characteristic absorption and dispersion signatures in the THz regime due to vibrational and rotational transitions. This implies that THz radiation might be used to examine the chemical composition of such compounds. Together, these properties make T-rays an excellent source for medical diagnostics and non destructive evaluation type of application. Yet, until late 1980s this part of the electromagnetic spectrum was least explored due to the technical difficulties involved in developing efficient and compact THz sources and detectors.