  High-resolution field localization in three dimensions is one of the main
challenges in optics and has immense importance in fields such as chemistry,
biology, and medicine. In order to generate the time reversed signal of a
monochromatic source \emph{discrete} sources that are modulated according to
the wave amplitude on a spherical envelope are required, rendering it
applicable only in acoustics. Here we approach these challenges by introducing
a spherical layer with a resonant permittivity, which naturally generates the
spatially \emph{continuous} time-reversed signal of an atomic and molecular
multipole transition at the origin. We start by utilizing a spherical layer
with a resonant TM $l=1$ permittivity situated in a uniform medium to generate
a free-space-subwavelength focal spot at the origin. We remove the degeneracy
of the eigenfunctions of the composite medium by situating a point current
source (or polarization) directed parallel to the spherical layer, which
generates a focal spot at the origin \emph{independently} of its location. The
free-space focal spot has a full width at half maximum of $0.4\lambda$ in the
lateral axes and $0.58\lambda$ in the axial axis, which is tighter by a factor
of $\sqrt{2}$ in each dimension in excitation-collection mode, overcoming the
$\lambda/2$ far-field resolution limit in three dimensions. We then explore two
directions to localize electric field with deep-subwavelength resolution in
three dimensions using this setup. In addition, we show that spherical
structures exhibit a new type of degeneracy in which an infinite number of
eigenvalues asymptotically coalesce. This high degeneracy results in a variety
of optical phenomena such as strong scattering and enhancement of absorption
and emission from an atom or molecule by orders of magnitude compared with a
standard resonance.
