Optics

Opticsis the branch of physicswhich involves the behaviour and properties of light, including its interactions with matterand the construction of instrumentsthat use or detectit. [ 1 ]Optics usually describes the behaviour of visible, ultraviolet, and infraredlight. Because light is an electromagnetic wave, other forms of electromagnetic radiationsuch as X-rays, microwaves, and radio wavesexhibit similar properties. [ 1 ] Most optical phenomena can be accounted for using the classical electromagneticdescription of light. Complete electromagnetic descriptions of light are, however, often difficult to apply in practice. Practical optics is usually done using simplified models. The most common of these, geometric optics, treats light as a collection of raysthat travel in straight lines and bend when they pass through or reflect from surfaces. Physical opticsis a more comprehensive model of light, which includes waveeffects such as diffractionand interferencethat cannot be accounted for in geometric optics. Historically, the ray-based model of light was developed first, followed by the wave model of light. Progress in electromagnetic theory in the 19th century led to the discovery that light waves were in fact electromagnetic radiation. Some phenomena depend on the fact that light has both wave-like and particle-like properties. Explanation of these effects requires quantum mechanics. When considering light's particle-like properties, the light is modelled as a collection of particles called " photons". Quantum opticsdeals with the application of quantum mechanics to optical systems. Optical science is relevant to and studied in many related disciplines including astronomy, various engineeringfields, photography, and medicine(particularly ophthalmologyand optometry). Practical applications of optics are found in a variety of technologies and everyday objects, including mirrors, lenses, telescopes, microscopes, lasers, and fibre optics. History Main article: History of optics See also: Timeline of electromagnetism and classical optics The Nimrud lens Optics began with the development of lenses by the ancient Egyptiansand Mesopotamians. The earliest known lenses, made from polished crystal, often quartz, date from as early as 700 BC for Assyrianlenses such as the Layard/ Nimrud lens. [ 2 ]The ancient RomansandGreeks filled glass ...philosophers, and the development of geometrical opticsin the Greco-Roman world. The wordopticscomes from the ancient Greekwordὀπτική, meaning "appearance, look". [ 3 ] Greek philosophyon optics broke down into two opposing theories on how vision worked, the " intromission theory" and the "emission theory". [ 4 ]The intro-mission approach saw vision as coming from objects casting off copies of themselves (called eidola) that were captured by the eye. With many propagators including Democritus, Epicurus, Aristotleand their followers, this theory seems to have some contact with modern theories of what vision really is, but it remained only speculation lacking any experimental foundation. Platofirst articulated the emission theory, the idea that visual perceptionis accomplished by rays emitted by the eyes.

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