  Inspired by the acoustic Helmholtz resonator, we propose a slit-box
electromagnetic nanoantenna able to concentrate the energy of an incident beam
into surfaces a thousand times smaller than with a classical lens. This design
gives birth to giant field intensity enhancement in hot volume, throughout the
slit. It reaches $10^4$ in the visible up to $10^8$ in the THz range even with
focused beams thanks to an omnidirectional reception. These properties could
target applications requiring extreme light concentration, such as SEIRA,
non-linear optics and biophotonics.
