Terahertz detection and imaging
Terahertz refers to electromagnetic waves with frequencies ranging from 0.1THz to 10 THz (wavelength from 3mm to 30μm), which are located between millimeter wave and infrared, and have both spectral characteristics. Terahertz wave has capability to penetrate non-metallic, non-polar materials and reveal information about their internal structure or detect objects hidden under such materials. Terahertz wave has relative weak penetration comparing to millimeter wave, whereas it has shorter wavelength and in theory it can obtain pictures with better resolution. Taking advantage of the “Fingerprint” characteristic of Terahertz spectrum, it is able to identified categories or components of materials via the molecular structure level, such as explosives, narcotics, etc. Terahertz wave has no ionizing radiation, which is safe to human and biological tissues.
By utilizing the changes in physical properties such as thermal and electrical properties of the terahertz-sensitive materials that inspired by terahertz wave, Terahertz wave detection technology convert incident terahertz wave into voltage or current signal for measurement, and thus obtaining terahertz wave strength information. Terahertz wave detection technology is one of the key topic in the field of terahertz science and technology. The aims of developing terahertz detectors are room-temperature operation, high sensitivity, quick response, and highly integrated arrays.
Terahertz imaging is divided into active and passive. Active imaging uses terahertz sources to emit specific frequencies of terahertz waves and irradiate the measured object, and uses terahertz detectors to receive terahertz signals reflected from the surface of the object, to obtain the intensity information of terahertz waves transmitted or reflected by the points of the object and then to form its terahertz image. Passive imaging uses a highly sensitive terahertz detector to receive the terahertz signal emitted by an object (usually the human body) itself, to obtain the intensity information of the terahertz wave emitted by various points of the human body, and then to form a terahertz image of the human surface. Hidden contrabands appear in Terahertz images as areas that differ from the surrounding light and darkness, presenting specific shapes or structures that can be used to determine whether a tested object contains or carries contrabands.
NUCTECH Terahertz Imaging Instrument adopts high frequency radiometer detector to receive the terahertz signal emitted from the human body to form a remote, non-contact and real-time terahertz image which can show the contrabands on the body surface. It can be used for security inspection at customs, civil aviation, loss and preventions, important events and other checkpoints.