Abstract
Efficient conversion of photonic to plasmonic energy is important for nano-optical applications, particularly imaging and spectroscopy. Recently a new generation of photonic/plasmonic transducers, the 'campanile' probes, has been developed that overcomes many shortcomings of previous near-field probes by efficiently merging broadband field enhancement with bidirectional coupling of far- to near-field electromagnetic modes. In this work we compare the properties of the campanile structure with those of current NSOM tips using finite element simulations. Field confinement, enhancement, and polarization near the apex of the probe are evaluated relative to local fields created by conical tapered tips in vacuum and in tip-substrate gap mode. We show that the campanile design has similar field enhancement and bandwidth capabilities as those of ultra-sharp metallized tips, but without the substrate and sample restrictions inherent in the tip-surface gap mode operation often required by those tips. In addition, we show for the first time that this campanile probe structure also significantly enhances the radiative rate of any dipole emitter located near the probe apex, quantifying the enhanced decay rate and demonstrating that over 90% of the light radiated by the emitter is "captured" by this probe. This is equivalent to collecting the light from a solid angle of ~3.6 pi. These advantages are crucial for performing techniques such as Raman and IR spectroscopy, white-light nano-ellipsometry and ultrafast pump-probe studies at the nanoscale.
Highlights
The design of advanced nanostructured materials can benefit from spectroscopic characterization techniques that provide chemical information with nanoscale spatial resolution
Optical near-field investigations can access this parameter space, but despite offering optical imaging and spectroscopy capabilities with sub-diffraction-limited resolution [1,2,3,4,5,6,7,8], the general applicability of near-field microscopy has been limited by the far-field to near-field coupling properties of its probes
A novel near-field probe structure [9, 10] – known as the “campanile” geometry – based on a design originally proposed by Staffaroni and Yablonovitch [11] has recently been shown to enable multidimensional nanospectroscopic imaging of nanostructures without many of the constraints and limitations encountered by previous near-field probes [9]
Summary
The design of advanced nanostructured materials can benefit from spectroscopic characterization techniques that provide chemical information with nanoscale spatial resolution. “Near-Field Scanning Optical Microscope with a Metallic Probe Tip,” Opt. Lett.
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