Terahertz Electric Field Imaging

Abstract

Various frequencies are spaced along the frequently used electromagnetic spectrum, including microwaves, infrared, visible light, and X rays. Terahertz radiation between microwave and infrared frequencies lies. In the electromagnetic spectrum, radiation at 1 THz has a period of 1 ps, a wavelength of 300 µm, a wave number of 33 cm −1 , photon energy of 4.1 meV, and an equivalent temperature of 47.6 K. In the same way that visible light can create a photograph, radio waves can transmit sound, and X rays can see shapes within the human body, terahertz waves (Trays) can create pictures and transmit information. Until recently, however, the very large terahertz portion of the spectrum has not been particularly useful because there were neither suitable emitters to send out controlled terahertz signals nor efficient sensors to collect them and record information. Recent developments in terahertz time‐domain spectroscopy and related terahertz technologies now lead one to view the world in a new way. As a result of developing research, terahertz radiation now has widespread potential applications in medicine, microelectronics, agriculture, forensic science, and many other fields. Three properties of THz wave radiation triggered research to develop this frequency band for applications and are discussed. Coherent terahertz time‐domain spectroscopy that has an ultrawide bandwidth provides a new method for characterizing the electronic, vibronic, and compositional properties of solid, liquid, and gas phase materials, as well as flames and flows. In theory, many biological and chemical compounds have distinct signature responses to terahertz waves due to their unique molecular vibrations and rotational energy levels, this implies that their chemical compositions might be examined using a terahertz beam. A T‐ray imaging modality would produce images that have “component contrast” enabling analysis of the water content and composition of tissues in biological samples. Such capability presents tremendous potential to identify early changes in composition and function as a precursor to specific medical investigations and treatment. Moreover, in conventional optical transillumination techniques that use near‐infrared pulses, large amounts of scattering can spatially smear out the objects to be imaged. T‐ray imaging techniques, due to their longer wavelengths, can provide significantly enhanced contrast as a result of low scattering (Rayleigh scattering).