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Optical Physics

Author: the photonics expert Dr. Rüdiger Paschotta (RP)

Optical physics is a discipline of physics which focuses on the fundamental study of light, specifically on its propagation in media and on its interactions with matter. It deals not only with visible light, but also with electromagnetic radiation in a wider range of optical frequencies – in particular, also with infrared light and ultraviolet light. Some aspects apply even in extreme frequency regions, such as the X-ray region.

Typical kinds of light interaction with matter are absorption and emission processes in various kinds of optical materials including not only largely transparent media such as optical glasses, but also doped insulators and semiconductors (both often used as laser gain media).

There is a substantial overlap with optics; however, the latter is an engineering discipline with substantial parts outside fundamental physics, e.g. dealing with the optimization of optical systems. Similarly, photonics involves a lot of optical physics, but also many other aspects of technology and applications. Optical physics can be considered as a fundamental scientific foundation for disciplines like optics and photonics.

Optical physics can be generally divided into classical optical and quantum optics:

• Classical optics deals with phenomena that can be described using classical electrodynamics, and can be further divided into
  • geometrical optics, treating light propagation in terms of geometric rays, and
  • wave optics (also called physical optics), taking into account the wave properties of light, thus involving effects like interference, diffraction and polarization. Particularly sophisticated physics are encountered in areas like photonic crystals and photonic metamaterials.
• Quantum optics, on the other hand, focuses on aspects of quantum physics. A fundamental concept is that of photons, which are involved in processes like spontaneous emission, stimulated emission (e.g. in lasers) and quantum entanglement phenomena.

Laser physics can be considered a special field of optical physics, focusing on aspects which are relevant for the operation of lasers and laser amplifiers.

Optical physics plays a crucial role in many areas of science and technology, including imaging, spectroscopy, information processing, and telecommunications. For instance, it is the fundamental science behind everyday technologies like illumination, lenses and microscopes, as well as more advanced technologies like lasers, optical fiber communications, quantum cryptography and quantum computing.

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Encyclopedia articles:

• optics
• wave optics
• geometrical optics

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