Methods and systems for generating and imaging THz electromagnetic radiation using a composite dipole array made up of novel structures of non-linear dipole strings with dual frequency resonances for frequency up conversion and frequency down conversion are disclosed. THz electromagnetic radiation resulting from the frequency down conversion process can be used as an illumination source for imaging, as a carrier for communications, or as an energy source for spectroscopy, for example. Optical electromagnetic radiation resulting from the frequency up conversion process can be used to form images from THz electromagnetic radiation for contraband detection, guidance systems, and medical applications, for example.