For: Opticks

Optics is the study of the behavior and properties of light including its interactions with matter and its detection by instruments. The word optics comes from , meaning appearance or look in ancient Greek.

Optics usually describes the behavior of visible, ultraviolet, and infrared light; however because light is an electromagnetic wave, similar phenomena occur in X-rays, microwaves, radio waves, and other forms of electromagnetic radiation and analogous phenomena occur with charged particle beams. Since the discovery by James Clerk Maxwell that light is electromagnetic radiation, optics has largely been regarded in theoretical physics as a sub-field of electromagnetism. Some optical phenomena depend on the quantum nature of light relating some areas of optics to quantum mechanics. In practice, the vast majority of optical phenomena can be accounted for using the classical electromagnetic description of light, as described by Maxwell's equations, resorting to phenomenological rules (e.g. Beer's Law, constitutive equations) to describe the interaction of light with matter. Even when still completely classical, complete electromagnetic descriptions of optical behavior are often difficult to apply to practical problems. This is why particular simplified models are used instead, notably those of geometrical optics and physical optics. These limited models adequately describe large subsets of optical phenomena while ignoring behavior that is insignificant for the system of interest.

The pure science of optics is called optical science or optical physics to distinguish it from applied optical sciences, which are referred to as optical engineering. Prominent subfields of optical engineering include illumination engineering, photonics, and optoelectronics. Some of these fields overlap, with nebulous boundaries between the subjects terms that mean slightly different things in different parts of the world and in different areas of industry. A professional community of researchers in nonlinear optics has developed in the last several decades due to advances in laser technology.

Optical science is relevant to and studied in many related disciplines including electrical engineering, psychology, and medicine (particularly ophthalmology and optometry).

History

main: History of optics

Classical optics

Before quantum optics became important, optics consisted mainly of the application of classical electromagnetism and its high frequency approximations to light. Classical optics divides into two main branches: geometric optics and physical optics.

Geometric optics, or ray optics, describes light propagation in terms of "rays". Rays are bent at the interface between two dissimilar media, and may be curved in a medium in which the refractive index is a function of position. The "ray" in geometric optics is an abstract object, or "instrument," which is perpendicular to the wavefronts of the actual optical waves (therefore collinear with the wave vector). Geometric optics provides rules for propagating these rays through an optical system, which indicates how the actual wavefront will propagate. This is a significant simplification of optics, and fails to account for many important optical effects such as diffraction and polarization. It is a good approximation, however, when the wavelength is very small compared with the size of structures with which the light interacts. Geometric optics can be used to describe the geometrical aspects of imaging, including optical aberrations.