Dichroism

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Dichroism

Dichroic redirects here. For the filter, see dichroic filter
Dichroic filter

A dichroic filter or thin-film filter is a very accurate color Filter used to selectively pass light of a small range of colors while Reflection other colors....
. For the glass, see dichroic glass
Dichroic glass

Dichroic glass is glass containing multiple micro-layers of metal oxides which give the glass dichroic optical properties. Dichroic glass was originally developed by NASA and its contractors for use in satellite optics and spacesuit visors....
.

Dichroism has two related but distinct meanings in optics

Optics

Optics is the study of the behavior and properties of light including its optical phenomena with matter and its imaging by optical instruments....
. A dichroic material is either one which causes visible light to be split up into distinct beams of different wavelength

Wavelength

In physics, wavelength is the distance between repeating units of a propagating wave of a given frequency. It is commonly designated by the Greek language letter lambda ....
s (colours) (not to be confused with dispersion

Dispersion (optics)

In optics, dispersion is the phenomenon in which the phase velocity of a wave depends on its frequency.Media having such a property are termed dispersive media....
), or one in which light rays having different polarization

Polarization

Polarization is a property of waves that describes the orientation of their oscillations. For transverse waves such as many electromagnetic waves, it describes the orientation of the oscillations in the plane perpendicular to the wave's direction of travel....
s are absorbed by different amounts.

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Encyclopedia

Dichroism has two related but distinct meanings in optics

Optics

Wavelength

Dispersion (optics)

Polarization

Greek language

Greek is an Indo-European languages native to the southern Balkan peninsula, the language of the Greek people. It forms an independent branch within Indo-European....
dikhroos, two-coloured, refers to any optical device which can split a beam of light into two beams with differing wavelengths. Such devices include mirror

Mirror

A mirror is an object with one surface polished, which leads to reflection and another opaque. The most familiar type of mirror is the plane mirror, which has a flat surface....
s and filter

Dichroic filter

A dichroic filter or thin-film filter is a very accurate color Filter used to selectively pass light of a small range of colors while Reflection other colors....
s, usually treated with optical coating

Optical coating

An optical coating is a thin-film optics of material deposited on an optical component such as a lens or mirror, which alters the way in which the optic Reflection and transmission light....
s, which are designed to reflect light over a certain range of wavelengths, and transmit light which is outside that range. An example is the dichroic prism

Dichroic prism

A dichroic prism is a prism that splits light into two beams of differing wavelength . They are usually constructed of one or more glass prisms with dichroism optical coatings that selectively reflect or transmit light depending on the light's wavelength....
, used in some camcorder

Camcorder

A camcorder is a portable consumer electronics device for recording video and Sound recording using a built-in recorder unit. The camcorder contains both a video camera and a video recorder in one unit, hence its compound name....
s, which uses several coatings to split light into red, green and blue components for recording on separate CCD arrays

Charge-coupled device

A charge-coupled device is an analog signal shift register that enables the transportation of analog signals through successive stages , controlled by a clock signal....
. This kind of dichroic device does not usually depend on the polarization of the light. The term dichromatic is also used in this sense.

The second meaning of dichroic refers to a material in which light in different polarization states travelling through it experience a varying absorption. The term came about because of early observations of the effect in crystal

Crystal

Tourmaline

Tourmaline is a crystal silicate mineral compounded with elements such as aluminium, iron, magnesium, sodium, lithium, or potassium. Tourmaline is classed as a semi-precious stone and the gem comes in a wide variety of colors....
. In these crystal

Crystal

A crystal or crystalline solid is a solid material whose constituent atoms, molecules, or ions are arranged in an orderly repeating pattern extending in all three spatial dimensions....
s, the strength of the dichroic effect varies strongly with the wavelength of the light, making them appear to have different colours when viewed with light having differing polarizations. This is more generally referred to as pleochroism

Pleochroism

Pleochroism is an optical phenomenon in which mineral grains within a Rock appear to be different colors when observed at different angles under a polarization petrographic microscope....
, and the technique can be used in mineralogy

Mineralogy

Mineralogy is an Earth Science focused around the chemistry, crystal structure, and physical properties of minerals. Specific studies within mineralogy include the processes of mineral origin and formation, classification of minerals, their geographical distribution, as well as their utilization....
to identify mineral

Mineral

A mineral is a naturally occurring solid formed through Geology processes that has a characteristic chemical composition, a highly ordered atomic structure, and specific physical properties....
s. In some materials, such as herapathite

Herapathite

Herapathite, or iodoquinine sulfate, is a chemical compound whose crystals are dichroism and thus can be used for polarization light.According to Edwin H....
(iodoquinine sulfate) or Polaroid

Polaroid

Polaroid is the name of a type of synthetic plastic sheet which is used to polarization light....
sheets, the effect is not strongly dependent on wavelength, and so the term dichroic is something of a misnomer, but still used.

Optically active molecule

Molecule

In chemistry, a molecule is defined as a sufficiently stable, electric charge neutral group of at least two atoms in a definite arrangement held together by very strong chemical bonds....
s exhibit differing absorption to light of opposite circular polarization

Circular polarization

In electrodynamics, circular polarization of electromagnetic radiation is a polarization such that the tip of the electric field vector, at a fixed point in space, describes a circle as time progresses....
. This is known as circular dichroism

Circular dichroism

Circular dichroism is the differential absorption of left- and right-handed circular polarization light.A CD Spectrometer is an instrument that records this phenomenon as a function of wavelength....
.

Which meaning of dichroic is intended can usually be inferred from the context. A mirror, filter, or beam splitter

Beam splitter

A beam splitter is an optical instrument that splits a beam of light in two. It is the crucial part of most Interferometrys.In its most common form, a cube, it is made from two triangular glass Prism s which are glued together at their base using Canada balsam....
is referred to as dichroic in the colour-separating first sense; a dichroic crystal or material refers to the polarization-absorbing second sense.

Dichroism in liquid crystals

Dichroism occurs in liquid crystals due to either the optical anisotropy of the molecular structure or the presence of impurities or the presence of dichroic dyes. The latter is also called a guest–host effect.

Dichroism

Dichroism in liquid crystals

See also