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In optics, an optical medium is material through which light and other electromagnetic waves propagate. It is a form of transmission medium . The permittivity and permeability of the medium define how electromagnetic waves propagate in it.
The dispersion relationship depends on the medium through which the waves propagate and on the type of waves (for instance electromagnetic, sound or water waves). The speed at which a resultant wave packet from a narrow range of frequencies will travel is called the group velocity and is determined from the gradient of the dispersion relation ...
Transmission medium, in physics and telecommunications, any material substance which can propagate waves or energy Active laser medium (also called gain medium or lasing medium), a quantum system that allows amplification of power (gain) of waves passing through (usually by stimulated emission) Optical medium, in physics, a material through ...
For waves that propagate in a medium, such as sound waves, the velocity of the observer and of the source are relative to the medium in which the waves are transmitted. [3] The total Doppler effect in such cases may therefore result from motion of the source, motion of the observer, motion of the medium, or any combination thereof.
Different fields of application have different definitions for the term. All the meanings are very similar in concept: In chemistry, the transmission coefficient refers to a chemical reaction overcoming a potential barrier; in optics and telecommunications it is the amplitude of a wave transmitted through a medium or conductor to that of the incident wave; in quantum mechanics it is used to ...
The weakness of the wave theory was that light waves, like sound waves, would need a medium for transmission. The existence of the hypothetical substance luminiferous aether proposed by Huygens in 1678 was cast into strong doubt in the late nineteenth century by the Michelson–Morley experiment .
At medium wave and shortwave frequencies (MF and HF bands) radio waves can refract from a layer of charged particles high in the atmosphere, called the ionosphere. This means that radio waves transmitted at an angle into the sky can be reflected back to Earth beyond the horizon, at great distances, even transcontinental distances.
In the 19th century, luminiferous aether (or ether), meaning light-bearing aether, was a theorized medium for the propagation of light. James Clerk Maxwell developed a model to explain electric and magnetic phenomena using the aether, a model that led to what are now called Maxwell's equations and the understanding that light is an ...