Optics

Introduction

Optics is a branch of physics that studies the behavior and properties of light, including its interactions with matter and the construction of instruments that use or detect it. Optics usually describes the behavior of visible, ultraviolet, and infrared light. Because light is an electromagnetic wave, other forms of electromagnetic radiation such as X-rays, microwaves, and radio waves exhibit similar properties.

A close-up of a lens focusing light rays.

Historical Overview

The earliest known lenses, made from polished crystal, often quartz, date from as early as 700 BC for Assyrian lenses such as the Layard/Nimrud lens. The ancient Egyptians made practical use of simple lenses. The Arab mathematician, Ibn Sahl, was the first to accurately describe the optics of lenses and curved mirrors in the 10th century.

Physical Optics

Physical optics, or wave optics, is the branch of optics that studies interference, diffraction, polarization, and other phenomena for which the ray approximation of geometric optics is not sufficient. It is usually concerned with the behavior of electromagnetic waves at the boundary of two dissimilar isotropic media.

Interference

Interference is the superposition of two or more waves resulting in a new wave pattern. As most commonly used, the term "interference" usually refers to the interaction of waves that are correlated or coherent with each other, either because they come from the same source or because they have the same or nearly the same frequency.

Diffraction

Diffraction refers to various phenomena that occur when a wave encounters an obstacle or a slit. It is defined as the bending of waves around the corners of an obstacle or aperture into the region of geometrical shadow of the obstacle. In classical physics, the diffraction phenomenon is described as the apparent bending of waves around small obstacles and the spreading out of waves past small openings.

Polarization

Polarization is a property applying to transverse waves that specifies the geometrical orientation of the oscillations. In a transverse wave, the direction of the oscillation is perpendicular to the direction of motion of the wave. A simple example of a polarized transverse wave is vibrations traveling along a taut string.

Geometrical Optics

Geometrical optics, or ray optics, describes light propagation in terms of rays. The ray in geometric optics is an abstraction useful for approximating the paths along which light propagates under certain circumstances.

Reflection

Reflection is the change in direction of a wavefront at an interface between two different media so that the wavefront returns into the medium from which it originated. Common examples include the reflection of light, sound and water waves.

Refraction

Refraction is the change in direction of a wave passing from one medium to another or from a gradual change in the medium. Refraction of light is the most commonly observed phenomenon, but other waves such as sound waves and water waves also experience refraction.

Dispersion

Dispersion in optics is the phenomenon in which the phase velocity of a wave depends on its frequency. Media having this common property may be termed "dispersive media". Sometimes the term "chromatic dispersion" is used for specificity.

Modern Optics

Modern optics encompasses the areas of optical science and engineering that became popular in the 20th century. These areas of optical science typically relate to the electromagnetic or quantum properties of light but do include other topics. A major subfield of modern optics, quantum optics, deals with specifically quantum mechanical properties of light.

Quantum Optics

Quantum optics is a branch of quantum physics that focuses primarily on the behavior of light, or photons. At the level of quantum optics, the behavior of individual photons has a bearing on the outcoming light, as opposed to classical optics, which was developed by Sir Isaac Newton.

Laser Optics

Laser optics involves the use of lasers, which are devices that emit light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. Lasers have many important applications. They are used in common consumer devices such as DVD players, laser printers, and barcode scanners.