Perfect mirror
Encyclopedia
A perfect mirror is a theoretical mirror
that reflects light
(and electromagnetic radiation
in general) perfectly, and doesn't transmit or absorb it.
Domestic mirrors are not perfect mirrors as they absorb a significant portion of the light
which falls on them.
Dielectric mirror
s are glass
or other substrates on which one or more layers of dielectric material are deposited, to form an optical coating
. A very complex dielectric mirror can reflect up to 99.999% of the light incident upon it, for a narrow range of wavelength
s and angles. A simpler mirror may reflect 99.9% of the light, but may cover a broader range of wavelengths.
Almost any dielectric material can act as a perfect mirror through total internal reflection
. This effect only occurs at shallow angles, however, and only for light inside the material. The effect happens when light goes from a medium with a higher index of refraction to one with a lower value (like air).
A new type of dielectric "perfect mirror" was developed in 1998 by researchers at MIT
.http://www.sciencemag.org/cgi/content/abstract/282/5394/1679?ijkey=ccf2d0db0d36ad06381205305f5c03c2f30b3bc5&keytype2=tf_ipsecsha These unusual mirrors are very efficient reflectors over a broad range of angles and wavelengths, and are insensitive to polarization. A version of the perfect mirror that was developed at MIT for military use is used by OmniGuide in laser surgery.
Mirror
A mirror is an object that reflects light or sound in a way that preserves much of its original quality prior to its contact with the mirror. Some mirrors also filter out some wavelengths, while preserving other wavelengths in the reflection...
that reflects light
Light
Light or visible light is electromagnetic radiation that is visible to the human eye, and is responsible for the sense of sight. Visible light has wavelength in a range from about 380 nanometres to about 740 nm, with a frequency range of about 405 THz to 790 THz...
(and electromagnetic radiation
Electromagnetic radiation
Electromagnetic radiation is a form of energy that exhibits wave-like behavior as it travels through space...
in general) perfectly, and doesn't transmit or absorb it.
Domestic mirrors are not perfect mirrors as they absorb a significant portion of the light
Light
Light or visible light is electromagnetic radiation that is visible to the human eye, and is responsible for the sense of sight. Visible light has wavelength in a range from about 380 nanometres to about 740 nm, with a frequency range of about 405 THz to 790 THz...
which falls on them.
Dielectric mirror
Dielectric mirror
A dielectric mirror is a type of a mirror composed of multiple thin layers of dielectric material, typically deposited on a substrate of glass or some other optical material. By careful choice of the type and thickness of the dielectric layers, one can design an optical coating with specified...
s are glass
Glass
Glass is an amorphous solid material. Glasses are typically brittle and optically transparent.The most familiar type of glass, used for centuries in windows and drinking vessels, is soda-lime glass, composed of about 75% silica plus Na2O, CaO, and several minor additives...
or other substrates on which one or more layers of dielectric material are deposited, to form an optical coating
Optical coating
An optical coating is one or more thin layers of material deposited on an optical component such as a lens or mirror, which alters the way in which the optic reflects and transmits light. One type of optical coating is an antireflection coating, which reduces unwanted reflections from surfaces, and...
. A very complex dielectric mirror can reflect up to 99.999% of the light incident upon it, for a narrow range of wavelength
Wavelength
In physics, the wavelength of a sinusoidal wave is the spatial period of the wave—the distance over which the wave's shape repeats.It is usually determined by considering the distance between consecutive corresponding points of the same phase, such as crests, troughs, or zero crossings, and is a...
s and angles. A simpler mirror may reflect 99.9% of the light, but may cover a broader range of wavelengths.
Almost any dielectric material can act as a perfect mirror through total internal reflection
Total internal reflection
Total internal reflection is an optical phenomenon that happens when a ray of light strikes a medium boundary at an angle larger than a particular critical angle with respect to the normal to the surface. If the refractive index is lower on the other side of the boundary and the incident angle is...
. This effect only occurs at shallow angles, however, and only for light inside the material. The effect happens when light goes from a medium with a higher index of refraction to one with a lower value (like air).
A new type of dielectric "perfect mirror" was developed in 1998 by researchers at MIT
Massachusetts Institute of Technology
The Massachusetts Institute of Technology is a private research university located in Cambridge, Massachusetts. MIT has five schools and one college, containing a total of 32 academic departments, with a strong emphasis on scientific and technological education and research.Founded in 1861 in...
.http://www.sciencemag.org/cgi/content/abstract/282/5394/1679?ijkey=ccf2d0db0d36ad06381205305f5c03c2f30b3bc5&keytype2=tf_ipsecsha These unusual mirrors are very efficient reflectors over a broad range of angles and wavelengths, and are insensitive to polarization. A version of the perfect mirror that was developed at MIT for military use is used by OmniGuide in laser surgery.