Near-field visualization of focal depth modulation by step corrugated plasmonic slits

摘要

Nanometric plasmonic slits with stepped corrugations have been designed and fabricated to achieve plasmonic focusing and focal depth modulation. A scanning near-field optical microscope is employed to directly visualize the transmitted light from the slits. The near-field and far-field two-dimensional images taken at different planes parallel to the slit surface unambiguously demonstrated the focusing effect of the nanoslits. Furthermore, by forming stepped corrugations with either a concave or a convex profile on both sides of the slits, the phase of the transmitted beam can be effectively manipulated, thus allowing an accurate tuning of the focal depth.