The SEED methodology is a nonlinear THz application that forces a searched for material's secondary emission signal to rise above the background 'white noise' like a flare or, in military jargon, a 'Red Star Cluster.'
In essence, a THz resonating harmonic frequency (2) (an 'external energy' excitation frequency) of the material (1) being searched for is transmitted.
If the material searched for is encountered by the transmitted excitation frequency, molecules of that material will be forced to absorb energy from the transmitted signal (3).
When the resonating THz frequency, or excitation energy, is removed, the molecules are forced to return to their lowest energy level...or ground state...and do so by releasing in all directions the absorbed excitation energy in what is called a 'secondary emission' (4)...a singularly unique spectral 'fingerprint' of relatively high energy that is based on the resonating THz frequency and the material's molecular absorption factors.
It is this secondary emission of explosive compositions that can be subsequently detected and identified from a standoff distance.