  Absorption of electromagnetic energy by a dissipative material is one of the
most fundamental electromagnetic processes that underlies a plethora of applied
problems, including sensing and molecular detection, radar detection, wireless
power transfer, and photovoltaics. Perfect absorption is a particular regime
when all of the incoming electromagnetic energy is absorbed by the system
without scattering. Commonly, the incident energy is delivered to the absorbing
system by a plane wave, hence perfect absorption of this wave requires an
infinitely extended planar structure. Here, we demonstrate theoretically that a
confined incident beam carrying a finite amount of electromagnetic energy can
be perfectly absorbed by a finite size deep subwavelength scatterer on a
substrate. We analytically solve the self-consistent scattering problem in the
dipole approximation and find a closed-form expression for the spatial spectrum
of the incident field and the required complex polarizability of the particle.
All analytical predictions are confirmed with full-wave simulations.
