Molecules resonate at specific, unique frequencies based upon material type. Thus, these frequencies serve as spectral 'fingerprints'...with no two molecules having the same frequency.

Terahertz frequencies, otherwise known as 'THz,' lie between the microwave and infrared (IR) frequencies.

What is THz?

Many material frequencies, especially for explosive compositions, lie within the THz spectrum.

In addition, THz waves have low photon energies—one million times weaker than x-rays—and will not cause harmful photoionization in biological tissues. In standard English, THz frequencies are fundamentally 'bio friendly'...meaning they're non-hazardous and will not sterilize men, cause dogs to twitch, force birds to crash & burn from the sky or, sad to say, heat your Meals Ready to Eat (MREs). THz, thus, provides a significant advantage for both imaging biological materials and in operational contexts where an operator or other subjects may be exposed to THz radiation.

THz can also penetrate or pass through a number of commonly used materials consequently allowing one to identify what's inside or underneath. This characteristic enhances THz's ability to be used in non-invasive and non-destructive inspections.

THz Applications - Linear

The second application, also passive, is called 'linear spectroscopy'...where a known THz frequency is applied to a material and the resulting spectrographic 'output' is analyzed to determine what that material is.

In essence, linear spectroscopy is the 'firing' of a 'THz bullet' at an unknown material that can eventually be identified based on the forensic analysis of the fragmented remnants of the THz bullet.

The major shortcomings of this approach are (1) the resulting THz 'fragmented remnants' are exceptionally low in energy and impossible to detect from a standoff distance; (2) the THz 'fragmented remnants' must be detected from a location opposite of the applied THz 'bullet'...tough to do when one does not know where an explosive is located to start with.

Thz Signal Remnant

While THz detection technologies are still in their infancy, there are two applications that have been explored to date.

The first application is THz imaging, a passive application...essentially, X-Rays on steroids...that still requires subjective interpretation of an image.


THz Imaging

"Well now, let me see, that's either a notebook,
a large sandwich, a brick of heroin or a block of C4?"


THz Pulse

THz Applications - Nonlinear Spectroscopy: SEED

The third & final application is SEED...Stimulated Emission Enhanced Detection - a non-passive, interrogative 'nonlinear spectroscopy' application where a known resonating THz frequency of the material in question is applied. If that material, an explosive in this case, is located within the frequency's sweep, the material will absorb some of the applied resonating frequency's energy.

This phenomenon is called 'excitation'...where the addition of a discrete amount of energy called excitation energy to a molecule results in a molecular alteration from its condition of lowest energy...or ground one of higher excited state.

More: The SEED Project