Achieving sub-diffraction imaging through bound surface states in negative-refracting photonic crystals at the near-infrared

We report the observation of imaging beyond the diffraction limit due to bound surface states in negative refraction photonic crystals. We achieve an effective negative index figure-of-merit [-Re($n)$/Im($n)$] of at least 380, $\sim $125$\times $ improvement over recent efforts in the near-infrared, with a 0.4 THz bandwidth. Supported by numerical and theoretical analyses, the observed near-field resolution is 0.47$\lambda $, clearly smaller than the diffraction limit of 0.61$\lambda $. Importantly, we show this sub-diffraction imaging is due to resonant excitation of surface slab modes, allowing evanescent wave amplification.