Near-field optics is that branch of

optics Optics is the branch of physics that studies the behaviour and properties of light, including its interactions with matter and the construction of instruments that use or detect it. Optics usually describes the behaviour of visible, ultra ...

that considers configurations that depend on the passage of

light Light or visible light is electromagnetic radiation that can be perceived by the human eye. Visible light is usually defined as having wavelengths in the range of 400–700 nanometres (nm), corresponding to frequencies of 750–420 te ...

to, from, through, or near an element with subwavelength features, and the coupling of that light to a second element located a subwavelength distance from the first. The barrier of spatial resolution imposed by the very nature of light itself in conventional

optical microscopy Optics is the branch of physics that studies the behaviour and properties of light, including its interactions with matter and the construction of instruments that use or detect it. Optics usually describes the behaviour of visible, ultraviol ...

contributed significantly to the development of near-field optical devices, most notably the near-field scanning optical microscope, or NSOM. The relatively new optical science of dressed photons (DPs) can also find its origin in near-field optics.

Size constraints

The limit of

optical resolution Optical resolution describes the ability of an imaging system to resolve detail, in the object that is being imaged. An imaging system may have many individual components, including one or more lenses, and/or recording and display components. ...

in a conventional

microscope A microscope () is a laboratory instrument used to examine objects that are too small to be seen by the naked eye. Microscopy is the science of investigating small objects and structures using a microscope. Microscopic means being invisibl ...

, the so-called

diffraction limit The resolution of an optical imaging system a microscope, telescope, or camera can be limited by factors such as imperfections in the lenses or misalignment. However, there is a principal limit to the resolution of any optical system, due to t ...

, is in the order of half the

wavelength In physics, the wavelength is the spatial period of a periodic wave—the distance over which the wave's shape repeats. It is the distance between consecutive corresponding points of the same phase on the wave, such as two adjacent crests, tr ...

of the light used to

image An image is a visual representation of something. It can be two-dimensional, three-dimensional, or somehow otherwise feed into the visual system to convey information. An image can be an artifact, such as a photograph or other two-dimensio ...

. Thus, when imaging at visible wavelengths, the smallest resolvable features are several hundred

nanometer 330px, Different lengths as in respect to the molecular scale. The nanometre (international spelling as used by the International Bureau of Weights and Measures; SI symbol: nm) or nanometer (American and British English spelling differences#-re, ...

s in size (although point-like sources, such as quantum dots, can be resolved quite readily). Using near-field optical techniques, researchers currently resolve features in the order of tens of nanometers in size. While other imaging techniques (e.g.

atomic force microscopy Atomic force microscopy (AFM) or scanning force microscopy (SFM) is a very-high-resolution type of scanning probe microscopy (SPM), with demonstrated resolution on the order of fractions of a nanometer, more than 1000 times better than the opt ...

and

electron microscopy An electron microscope is a microscope that uses a beam of accelerated electrons as a source of illumination. As the wavelength of an electron can be up to 100,000 times shorter than that of visible light photons, electron microscopes have a ...

) can resolve features of much smaller size, the many advantages of optical microscopy make near-field optics a field of considerable interest.

History

The notion of developing a near-field optical device was first conceived by Edward Hutchinson Synge in 1928 but was not realized experimentally until the 1950s when several researchers demonstrated the feasibility of sub-wavelength resolution. Published images of sub-wavelength resolution appeared when Ash and Nichols examined gratings with line spacing less than one

millimeter file:EM Spectrum Properties edit.svg, 330px, Different lengths as in respect to the electromagnetic spectrum, measured by the metre and its derived scales. The microwave is between 1 meter to 1 millimeter. The millimetre (American and British Eng ...

using

microwave Microwave is a form of electromagnetic radiation with wavelengths ranging from about one meter to one millimeter corresponding to frequency, frequencies between 300 MHz and 300 GHz respectively. Different sources define different fre ...

s of 3 cm wavelength. In 1982 Dieter Pohl at IBM in Zurich, Switzerland, first obtained sub-wavelength resolution at visible wavelengths using near-field optical techniques.

References

Physical optics {{Optics-stub

Size constraints

History

See also

References