Berlin 2008 – wissenschaftliches Programm

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DS: Fachverband Dünne Schichten

DS 37: Vibrational Spectroscopy of Nanolayers with Optical Probes

DS 37.3: Vortrag

Freitag, 29. Februar 2008, 14:30–14:45, H 2013

Creation of highly confined longitudinal field modes for near-field excitation — •Johannes Stadler, Catrinel Stanciu, and Alfred Meixner — Institut of Physical Chemistry, University of Tuebingen, Germany

The focusing properties of a confocal microscope are not only crucial to enhance the resolution for confocal microscopy, but also define the confinement and thus the local field strength in the focus. In particular for tip-enhanced microscopy, having a tightly focused beam is extremely important in order to avoid having a strong background overlapping the tip-enhanced signals. More important, the polarization of light in the focal area should be longitudinal to efficiently excite the metallic tips. We show here that a parabolic mirror (PM) fulfils both requirements when used as a focusing element for tip-enhanced microscopy. When using a radially-polarized beam, the PM provides the smallest diffraction-limited spot that can be created using far-field optics. Due to the different focusing properties and apodization factors of the PM, the intensity in the longitudinal mode is remarkably higher than in comparable setups using aplanar lenses. The strong longitudinal fields and the local confinement offer perfect conditions for the excitation of a near-field tip with fewer background noise. First examples of near-field optical easurements with this new arrangement will be presented.