1. Introduction 2. Theoretical foundations 3. Propagation and focusing of optical fields 4. Spatial resolution and position accuracy 5. Nanoscale optical microscopy 6. Near-field optical probes 7. Probe-sample distance control 8. Light emission and optical interaction in nanoscale environments 9. Quantum emitters 10. Dipole emission near planar interfaces 11. Photonic crystals and resonators 12. Surface plasmons 13. Forces in confined fields 14. Fluctuation-induced phenomena 15. Theoretical methods in nano-optics Appendices Index.

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Principles of nano-optics

We present an experimental and theoretical study of the fluorescence rate of a single molecule as a function of its distance to a laser-irradiated gold nanoparticle. The local field enhancement leads to an increased excitation rate whereas nonradiative energy transfer to the particle leads to a decrease of the quantum yield (quenching). Because of these competing effects, previous experiments showed either fluorescence enhancement or fluorescence quenching. By varying the distance between molecule and particle we show the first experimental measurement demonstrating the continuous transition from fluorescence enhancement to fluorescence quenching. This transition cannot be explained by treating the particle as a polarizable sphere in the dipole approximation.

https://www.photonics.ethz.ch/fileadmin/user_upload/FILES2SHARE/anger06a.pdf

Enhancement and quenching of single-molecule fluorescence.

An overview of the recent developments in the field of cylindrical vector beams is
provided. As one class of spatially variant polarization, cylindrical vector beams
are the axially symmetric beam solution to the full vector electromagnetic wave
equation. These beams can be generated via different active and passive methods.
Techniques for manipulating these beams while maintaining the polarization symmetry
have also been developed. Their special polarization symmetry gives rise to unique
high-numerical-aperture focusing properties that find important applications in
nanoscale optical imaging and manipulation. The prospects for cylindrical vector
beams and their applications in other fields are also briefly discussed.

Cylindrical vector beams: from mathematical concepts to applications

Cylindrical-vector beams are of increasing recent interest for their role in novel laser resonators and their applications to electron acceleration and scanning microscopy. In this paper, we calculate cylindrical-vector fields, near the focal region of an aplanatic lens, and briefly discuss some applications. We show that, in the particular case of a tightly focused, radially polarized beam, the polarization shows large inhomogeneities in the focal region, while the azimuthally polarized beam is purely transverse even at very high numerical apertures.

Focusing of high numerical aperture cylindrical-vector beams.

Light is often thought of in terms of radial polarization, but longitudinal polarization is also possible, and it has some intriguing possibilities for particle acceleration. Binary optics, combined with a high-numerical-aperture lens, is a potential route to achieving light with this unusual property.

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Creation of a needle of longitudinally polarized light in vacuum using binary optics

We demonstrate that a strong longitudinal, nonpropagating field is generated at the focus of a radially polarized beam mode. This field is localized in space and its energy density exceeds the energy density of the transverse field by more than a factor of 2. Single molecules with fixed absorption dipole moments are used to probe the longitudinal field. Vice versa, it is demonstrated that orientations of single molecules are efficiently mapped out in three dimensions by using a radially polarized beam as the excitation source. We also show that there is no momentum or energy transport associated with the longitudinal field.

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Longitudinal Field Modes Probed by Single Molecules

Dark-field illumination provides an imaging mode that rejects specular light, thereby highlighting edge features. We analyze dark-field imaging by using cylindrical vector beam illumination with a confocal microscope equipped with a microstructure fiber mode filter. A numerical model based on rigorous coupled-wave analysis has been used to analyze the method. We acquired images of separated edges features to investigate the edge separation resolution of the method. A through-focus comparison of azimuthal and radial polarization shows a measurable dependence of edge separation on polarization.

Dark-field imaging with cylindrical-vector beams

Polarization control and analysis have proven to be a powerful tool both in conventional and confocal microscopies, but most of these approaches have used homogeneously polarized pupils Other groups have had varying levels of success producing beams with spatially inhomogeneous polarization In this paper, we describe the generation and focusing properties of such beams and their application to scanning laser microscopy We specifically consider microscopy using the lowest-order azimuthally polarized beam

Inhomogenous polarization in scanning optical microscopy

An apparatus for producing an inhomogeneously polarized optical beam from a homogeneously polarized input optical beam includes a first phase shifter, a second phase shifter, and one or more polarization beam splitters. The first phase shifter shifts at least one portion of a first part of the input optical beam by a first phase. The second phase shifter shifts at least one portion of a second part of the input optical beam by substantially the first phase. The one or more polarization beam splitters split the input optical beam into the first part and the second part and combine the phase shifted portion and substantially all other portions of the first part of the input optical beam with the phase shifted portion and substantially all other portions of the second part of the input optical beam to produce the inhomogeneously polarized optical beam.

Kathleen S. Youngworth

Papers

Focusing of high numerical aperture cylindrical-vector beams.

Longitudinal Field Modes Probed by Single Molecules

Dark-field imaging with cylindrical-vector beams

Inhomogenous polarization in scanning optical microscopy

Apparatus for production of an inhomogeneously polarized optical beam for use in illumination and a method thereof