Flat lens and device for terahertz-band multi-angle annular uniform illumination

The invention discloses a flat lens and device for terahertz frequency band multi-angle annular uniform illumination, and relates to the field of terahertz active imaging. According to the invention, the emergent surface of the flat lens with the air hole array and the central point defect is provided with a plurality of annular grooves or is constructed into a random rough surface, so that a terahertz light beam irradiated by a terahertz source and having Gaussian distribution can be converted into an annular uniform illumination light beam emitted at multiple angles; terahertz waves can illuminate a target from different angles, reflected wave signals entering a detection system are increased, and the Terahertz waves have outstanding application value in application scenes of the fields of nondestructive detection, human body security inspection and the like. Moreover, in the reflection-type terahertz active imaging system, compared with a circular light beam, the annular light beam can convert small-angle