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

The near-field optical interaction between a sharp probe and a sample of interest can be exploited to image, spectroscopically probe, or modify surfaces at a resolution (down to ∼12 nm) inaccessible by traditional far-field techniques. Many of the attractive features of conventional optics are retained, including noninvasiveness, reliability, and low cost. In addition, most optical contrast mechanisms can be extended to the near-field regime, resulting in a technique of considerable versatility. This versatility is demonstrated by several examples, such as the imaging of nanometric-scale features in mammalian tissue sections and the creation of ultrasmall, magneto-optic domains having implications for highdensity data storage. Although the technique may find uses in many diverse fields, two of the most exciting possibilities are localized optical spectroscopy of semiconductors and the fluorescence imaging of living cells.

https://science.sciencemag.org/content/sci/257/5067/189.full.pdf

Near-Field Optics: Microscopy, Spectroscopy, and Surface Modification Beyond the Diffraction Limit

In near-field scanning optical microscopy, a light source or detector with dimensions less than the wavelength (lambda) is placed in close proximity (lambda/50) to a sample to generate images with resolution better than the diffraction limit. A near-field probe has been developed that yields a resolution of approximately 12 nm ( approximately lambda/43) and signals approximately 10(4)- to 10(6)-fold larger than those reported previously. In addition, image contrast is demonstrated to be highly polarization dependent. With these probes, near-field microscopy appears poised to fulfill its promise by combining the power of optical characterization methods with nanometric spatial resolution.

http://science.sciencemag.org/content/sci/251/5000/1468.full.pdf

Breaking the Diffraction Barrier: Optical Microscopy on a Nanometric Scale

Near‐field optical‐scanning (NFOS) microscopy or ‘‘optical stethoscopy’’ provides images with resolution in the 20‐nm range, i.e., a very small fraction of an optical wavelength. Scan images of metal films with fine structures presented in this paper convincingly demonstrate this resolution capability. Design of an NFOS microscope with tunnel distance regulation, its theoretical background, application potential, and limitations are discussed.

Near‐field optical‐scanning microscopy

We present the design and describe the operation of a scanning probe microscope which simultaneously provides the attractive mode force and near‐field optical images of objects. In this technique, the force signal is used to track the topography, thus allowing the optical signal primarily to show variations in transmissivity. A number of results are presented on the application of the technique to imaging different samples.

Near‐field differential scanning optical microscope with atomic force regulation

The resolution of near‐field optical scanning microscopy (NFOS) is determined by the dimensions of the microscopic light source rather than the diffraction limit. To demonstrate NFOS in reflection, intensity changes in the (backward) scattering from a 70–100 nm diam hole in a metal film were recorded while the sample was scanned in close proximity to this aperture. Raster‐scan images of a planar metal test pattern yield a resolution comparable to the size of the aperture.

Near‐field optical scanning microscopy in reflection

The resolution of contact imaging with light is limited by the distance between object and image and not by the wavelength. Contact imaging with visible light at submicroscopic resolution (100 nm) is demonstrated using the concept of imaging by energy transfer. The bleaching of a dye is inhibited by energy transfer to a metal in close proximity. This mechanism is exploited for imaging a planar metal pattern onto a film of a cyanine dye.

Submicroscopic contact imaging with visible light by energy transfer

SUMMARY

SNOM is a non-contact stylus microscopy analogous to STM. Optical near-field interaction is used to sense approach and optical properties on the nanometre scale (≅1 nm normal, 20–50 nm lateral). SNOM was demonstrated in transmission and reflection, in a topographic mode, and with amplitude as well as phase objects. The excitation of plasmons in the SNOM ‘tip’, a very recent development, greatly enhances sensitivity and permits intriguing new optical experiments. Overcoming the limit of diffraction, SNOM turns a long-held dream of optical microscopists into reality.

U. Ch. Fischer

Papers

Near‐field optical scanning microscopy in reflection

Submicroscopic contact imaging with visible light by energy transfer

Scanning near-field optical microscopy (SNOM)