Enhanced image contrast with delocalized near-field excitation

For Tip Enhanced Near‐field Optical Microscopy (TENOM) utilizing detection of fluorescence or Raman emission, signal to noise amplification is highly desirable for higher resolution imaging. This goal may be achieved by amplifying the signal produced by the probe at the sample through a highly resonant geometry and/or by filtering out the unwanted signal of the excitation source through the addition of an aperture in the collection optical pathway. Making highly resonant tip geometries via nanofabrication can be a difficult process, while the aperture method is a much easier method. With this technique, even tips with undesirably low resonance can be utilized for imaging. We demonstrate the concept through the use of a low field enhancement probe by showing the spatial separation of the excitation and field enhancement locations. We also are able to predict this effect using finite difference time domain modeling of the potential geometries for a desired wavelength. Making highly resonant tip geometries via nanofabrication can be a difficult process, while the aperture/detector method is a much easier to implement. With this technique, even tips with undesirably low resonance can be utilized for imaging. We demonstrate the concept through the use of a low field enhancement probe by showing the spatial separation of the excitation and field enhancement locations and the associated numerical modeling.