On the coupling and transmission of transverse and longitudinal fields into fully metal-coated optical nano-probes
Fully-metal-coated near-field optical probes, based on a cantilever design, have been studied theoretically and experimentally. Numerical simulations prove that these structures allow non-zero modal emission of the electromagnetic field trough a 60 nm thick metallic layer, that is opaque when deposited on flat substrates. The far-field intensity patterns recorded experimentally correspond to the ones calculated for the fundamental and first excited LP modes. Moreover, this study demonstrates that a high confinement of the electromagnetic energy can be reached in the near-field, when illuminated with radially polarized light. Finally, it was verified that the confinement of the field depends on the volume of the probe apex. The coupling and transmission of transverse and longitudinal fields into the probes has been also investigated. Two kinds of probes with different metal coating roughness are considered. Transverse and longitudinal field distributions are obtained by focusing azimuthally and radially polarized beams produced by means of a liquid crystal plate. The focal plane is scanned using microfabricated probes in a collection mode configuration. It is found that the roughness of the metal coating plays an important role in the coupling strength of transverse fields into the probes: the relative coupling efficiency for transverse fields diminishes with a rough metal coating, while that of longitudinal fields does not.
Record created on 2009-05-12, modified on 2016-08-08