Abstract
Using an unique home-made THz near-field microscope, we demonstrate a perfect cavity for electromagnetic radiation at THz frequencies. This cavity consists of a periodic array of gold rods, or metasurface, designed to fully suppress the radiation leakage. This suppression of radiation losses, in combination with the negligible material losses of gold at THz frequencies, makes it possible to trap electromagnetic waves for arbitrarily long times to the array. The mechanisms responsible for this light trapping and how to observe it in the near-field will be discussed in detail.