  Optical imaging beyond the diffraction limit was one of the primary
motivations for negative-index metamaterials, resulting in Pendry's perfect
lens and the more attainable superlens. While these approaches offer
sub-diffractional resolution, they do not provide a mechanism for magnification
of the image. Hyperbolic (or indefinite-permittivity) metamaterials have been
theoretically considered and experimentally demonstrated to provide
simultaneously subdiffractive imaging and magnification; however, they are
plagued with low efficiency and complex fabrication. In this work, we present
theoretical and experimental studies of near-field optical imaging through a
flat slab of the low-loss, natural hyperbolic material, hexagonal boron nitride
(hBN). This thin hBN layer exhibits wavelength-dependent multifunctional
operations, offering both an enhanced near-field imaging of single buried
objects with down to lambda/32 resolution (0.4 um at lambda=12.8 um), as well
as enabling an enlarged reconstruction of the geometric outline of the
investigated objects. Both the excellent resolution and the multifunctional
operation can be explained based on the volume-confined, wavelength-dependent
propagation angle of Type I hyperbolic polaritons. Our results provide both the
understanding of near-field imaging performance through this natural hyperbolic
media, as well as inspire their exciting potential for guiding and sensing of
light at an extreme sub-diffractional scale.
