Multifrequency Digital Terahertz Holography Within 1.39-4.25 THz Range

Terahertz (THz) multifrequency digital holography within the range from 1.39-4.25 THz is demonstrated. Holograms are recorded using an optically pumped molecular THz laser operating at emission lines of 1.39-, 2.52-, 3.11-, and 4.25 THz frequencies, and nanometric field effect transistor with integrated patch antennae as a THz detector. It is revealed that phase-shifting methods allow for qualitative reconstruction of multifrequency THz holograms combined into one "colored" image. It provides more information about the low-absorbing objects with additionally improved quality achieved by removing unwanted information related to the so-called dc term and conjugated beam forming a virtual image. It is shown that the THz holography can be applied for the investigation of low-absorbing objects, and it is illustrated via inspection of stacked graphene layers placed on a high-resistivity silicon substrate.