Nanophotonics or Nano-optics deals with the application of optics or light interaction with the particles or substances on length scales. It is actually the study of behavior of light. Nanophotonics is the branch of Nano-optics which deals with the optical methods to make lenses, microscopes, telescopes and many other instruments by utilizing the properties of light. Nano-optics has various technologies including near-field scanning optical microscopy (NSOM, for nanostructure investigation), scanning tunneling microscopy (STM), atomic force microscopy (AFM) and Surface Plasmon Optics (interact strongly with light). In order to increase the resolution of light on diffractive elements, traditional microscopy is used.

But because of some limits of diffractive elements, transmission of light may be focused roughly with a minimum diameter of wavelength of light. Diffraction limit is also known as the "Rayleigh Criterion" (A rule for how finely a set of optics may be able to distinguish the location of objects that are near each other). In order to increase the maximum resolution with diffraction-limited microscopy, it would be obtainable on hundred nanometers. Alternative techniques are being utilized on a nanometer scale in order to get interest in the characterization of materials.
Moreover, scientific communities are becoming more engrossed by using these techniques.

For example, Scanning Probe Microscopy (SPM, a branch of microscopy that forms images of surfaces using a physical probe that scans the specimen) transmits native information from a sample. Some devices has been developed that can be fabricated in nano-scale which provides the best area of study. This study would revolutionize various industries by providing all optical instruments on a chip. Two broad themes have been involved in the study of nanophotonics;

• At the nanometer scale novel properties of light are studying
• For the engineering applications highly powerful devices are enabling

Nanophotonics usually refers to occurrences of ultraviolet, visible, and near infra-red light having wavelength of 300 to 1200 nanometers. Having interaction of light with the nano-scale structures, this would lead to the detention of the electromagnetic field to the surface of nanostructure resulting in an optical near field. The interaction of light with the nanostructures having shape and size, electromagnetic field will be dependent on. A surface bound optical oscillation, which we also call it optical near field, can vary on length scale of hundreds of nanometers; this length scale would be smaller than the wavelength of light.

Extremely small size of materials can result in novel optical properties. Colloidal gold is an example of this type of effect having color change. By determining material's optical response, the material's intrinsic properties can be changed in addition to extrinsic effects. If the size of particle is even smaller this size effect will surely occur. And because of this some intrinsic properties of the material might be changed. A typical example is the semi-conductor nanostructures in which small size of particle limits the quantum mechanical wave-function that leads to discrete optical transitions, for example, fluorescence colors are dependent on the particle size. The color change effect is due to bandgap or energy gap (an energy range in a solid where no electron state can exist). When we refer to nano-optics, this effect is not directly associated with optical wavelength.

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