A report on Refractive index

$A ray of light being refracted in a plastic block$

$Refraction of a light ray$

$Thomas Young coined the term index of refraction.$

$Diamonds have a very high refractive index of 2.417.$

$A split-ring resonator array arranged to produce a negative index of refraction for microwaves$

$In optical mineralogy, thin sections are used to study rocks. The method is based on the distinct refractive indices of different minerals.$

$Light of different colors has slightly different refractive indices in water and therefore shows up at different positions in the rainbow.$

$In a prism, dispersion causes different colors to refract at different angles, splitting white light into a rainbow of colors.$

$The variation of refractive index with wavelength for various glasses. The shaded zone indicates the range of visible light.$

The colors of a soap bubble are determined by the optical path length through the thin soap film in a phenomenon called thin-film interference.

$Refraction of light at the interface between two media of different refractive indices, with n2 > n1. Since the phase velocity is lower in the second medium (v2 < v1), the angle of refraction θ2 is less than the angle of incidence θ1; that is, the ray in the higher-index medium is closer to the normal.$

Total internal reflection can be seen at the air-water boundary.

$The power of a magnifying glass is determined by the shape and refractive index of the lens.$

$The relation between the refractive index and the density of silicate and borosilicate glasses$

$A calcite crystal laid upon a paper with some letters showing double refraction$

Birefringent materials can give rise to colors when placed between crossed polarizers. This is the basis for photoelasticity.

$A gradient-index lens with a parabolic variation of refractive index (n) with radial distance (x). The lens focuses light in the same way as a conventional lens.$

$The principle of many refractometers$

$A handheld refractometer used to measure the sugar content of fruits$

A differential interference contrast microscopy image of yeast cells

Optical medium is a dimensionless number that gives the indication of the light bending ability of that medium.

- Refractive index

$A ray of light being refracted in a plastic block$

81 related topics with Alpha

Light

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Electromagnetic radiation within the portion of the electromagnetic spectrum that is perceived by the human eye.

The electromagnetic spectrum, with the visible portion highlighted

Beam of sun light inside the cavity of Rocca ill'Abissu at Fondachelli-Fantina, Sicily

$Due to refraction, the straw dipped in water appears bent and the ruler scale compressed when viewed from a shallow angle.$

Hong Kong illuminated by colourful artificial lighting.

$Thomas Young's sketch of a double-slit experiment showing diffraction. Young's experiments supported the theory that light consists of waves.$

where θ1 is the angle between the ray and the surface normal in the first medium, θ2 is the angle between the ray and the surface normal in the second medium and n1 and n2 are the indices of refraction, n = 1 in a vacuum and n > 1 in a transparent substance.

Optics

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Branch of physics that studies the behaviour and properties of light, including its interactions with matter and the construction of instruments that use or detect it.

Alhazen (Ibn al-Haytham), "the father of Optics"

$Reproduction of a page of Ibn Sahl's manuscript showing his knowledge of the law of refraction.$

The first treatise about optics by Johannes Kepler, Ad Vitellionem paralipomena quibus astronomiae pars optica traditur (1604)

Cover of the first edition of Newton's Opticks (1704)

$Geometry of reflection and refraction of light rays$

Illustration of Snell's Law for the case n1 < n2, such as air/water interface

A ray tracing diagram for a converging lens.

Images of black letters in a thin convex lens of focal length f are shown in red. Selected rays are shown for letters E, I and K in blue, green and orange, respectively. Note that E (at 2f) has an equal-size, real and inverted image; I (at f) has its image at infinity; and K (at f/2) has a double-size, virtual and upright image.

When oil or fuel is spilled, colourful patterns are formed by thin-film interference.

Conceptual animation of light dispersion through a prism. High frequency (blue) light is deflected the most, and low frequency (red) the least.

Dispersion: two sinusoids propagating at different speeds make a moving interference pattern. The red dot moves with the phase velocity, and the green dots propagate with the group velocity. In this case, the phase velocity is twice the group velocity. The red dot overtakes two green dots, when moving from the left to the right of the figure. In effect, the individual waves (which travel with the phase velocity) escape from the wave packet (which travels with the group velocity).

A polariser changing the orientation of linearly polarised light. In this picture, θ1 – θ0 = θi.

The effects of a polarising filter on the sky in a photograph. Left picture is taken without polariser. For the right picture, filter was adjusted to eliminate certain polarizations of the scattered blue light from the sky.

Experiments such as this one with high-power lasers are part of the modern optics research.

Model of a human eye. Features mentioned in this article are 1. vitreous humour 3. ciliary muscle, 6. pupil, 7. anterior chamber, 8. cornea, 10. lens cortex, 22. optic nerve, 26. fovea, 30. retina

The Ponzo Illusion relies on the fact that parallel lines appear to converge as they approach infinity.

Illustrations of various optical instruments from the 1728 Cyclopaedia

A colourful sky is often due to scattering of light off particulates and pollution, as in this photograph of a sunset during the October 2007 California wildfires.

is the refractive index of the second material.

$A ray of light being refracted in a plastic block.$

Refraction

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Redirection of a wave as it passes from one medium to another.

$A ray of light being refracted in a plastic block.$

$A pen partially submerged in a bowl of water appears bent due to refraction at the water surface.$

When a wave moves into a slower medium the wavefronts get compressed. For the wavefronts to stay connected at the boundary the wave must change direction.

$A pencil part immersed in water looks bent due to refraction: the light waves from X change direction and so seem to originate at Y.$

$An image of the Golden Gate Bridge is refracted and bent by many differing three-dimensional drops of water.$

$The sun appears slightly flattened when close to the horizon due to refraction in the atmosphere.$

Heat haze in the engine exhaust above a diesel locomotive.

$Water waves are almost parallel to the beach when they hit it because they gradually refract towards land as the water gets shallower.$

For light, refraction follows Snell's law, which states that, for a given pair of media, the ratio of the sines of the angle of incidence θ1 and angle of refraction θ2 is equal to the ratio of phase velocities (v1 / v2) in the two media, or equivalently, to the refractive indices (n2 / n1) of the two media.

$In a dispersive prism, material dispersion (a wavelength-dependent refractive index) causes different colors to refract at different angles, splitting white light into a spectrum.$

Dispersion (optics)

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Phenomenon in which the phase velocity of a wave depends on its frequency; sometimes the term chromatic dispersion is used for specificity to optics in particular.

$In a dispersive prism, material dispersion (a wavelength-dependent refractive index) causes different colors to refract at different angles, splitting white light into a spectrum.$

A compact fluorescent lamp seen through an Amici prism

$The variation of refractive index vs. vacuum wavelength for various glasses. The wavelengths of visible light are shaded in grey.$

Most often, chromatic dispersion refers to bulk material dispersion, that is, the change in refractive index with optical frequency.

$Partial transmission and reflection of a pulse travelling from a low to a high refractive index medium.$

Fresnel equations

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Interface between different optical media.

$Partial transmission and reflection of a pulse travelling from a low to a high refractive index medium.$

The plane of incidence is defined by the incoming radiation's propagation vector and the normal vector of the surface.

When light strikes the interface between a medium with refractive index n1 and a second medium with refractive index n2, both reflection and refraction of the light may occur.

Total internal reflection

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Optical phenomenon in which waves arriving at the interface (boundary) from one medium to another (e.g., from water to air) are not refracted into the second ("external") medium, but completely reflected back into the first ("internal") medium.

Fig.2:Repeated total internal reflection of a 405nm laser beam between the front and back surfaces of a glass pane. The color of the laser light itself is deep violet; but its wavelength is short enough to cause fluorescence in the glass, which re-radiates greenish light in all directions, rendering the zigzag beam visible.

Fig.3:Total internal reflection of light in a semicircular acrylic block.

Fig.7:Total internal reflection by the water's surface at the shallow end of a swimming pool. The broad bubble-like apparition between the swimmer and her reflection is merely a disturbance of the reflecting surface. Some of the space above the water level can be seen through "Snell's window" at the top of the frame.

Fig.9:Depiction of an incident sinusoidal plane wave (bottom) and the associated evanescent wave (top), under conditions of total internal reflection. The reflected wave is not shown.

Fig.10:Disembodied fingerprints visible from the inside of a glass of water, due to frustrated total internal reflection. The observed fingerprints are surrounded by white areas where total internal reflection occurs.

Fig.14:Porro prisms (labeled 2 & 3) in a pair of binoculars.

An Indian triggerfish and its total reflection in the water's surface.

Total reflection of a paintbrush by the water-air surface in a glass.

Total internal reflection of a green laser in the stem of a wine glass.

It occurs when the second medium has a higher wave speed (i.e., lower refractive index) than the first, and the waves are incident at a sufficiently oblique angle on the interface.

Wavelength

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Spatial period of a periodic wave—the distance over which the wave's shape repeats.

Sinusoidal standing waves in a box that constrains the end points to be nodes will have an integer number of half wavelengths fitting in the box.

A standing wave (black) depicted as the sum of two propagating waves traveling in opposite directions (red and blue)

Wavelength is decreased in a medium with slower propagation.

$Refraction: upon entering a medium where its speed is lower, the wave changes direction.$

Separation of colors by a prism (click for animation)

Various local wavelengths on a crest-to-crest basis in an ocean wave approaching shore

A sinusoidal wave travelling in a nonuniform medium, with loss

A wave on a line of atoms can be interpreted according to a variety of wavelengths.

Wavelength of a periodic but non-sinusoidal waveform.

Pattern of light intensity on a screen for light passing through two slits. The labels on the right refer to the difference of the path lengths from the two slits, which are idealized here as point sources.

$Diffraction pattern of a double slit has a single-slit envelope.$

Relationship between wavelength, angular wavelength, and other wave properties.

For electromagnetic waves the speed in a medium is governed by its refractive index according to

Lens

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Transmissive optical device which focuses or disperses a light beam by means of refraction.

$Light being refracted by a spherical glass container full of water. Roger Bacon, 13th century$

Lens for LSST, a planned sky surveying telescope

The position of the focus of a spherical lens depends on the radii of curvature of the two facets.

A camera lens forms a real image of a distant object.

Virtual image formation using a positive lens as a magnifying glass.

Chromatic aberration is caused by the dispersion of the lens material—the variation of its refractive index, n, with the wavelength of light.

$A calcite crystal laid upon a graph paper with blue lines showing the double refraction$

Birefringence

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$A calcite crystal laid upon a graph paper with blue lines showing the double refraction$

$In this example, optic axis along the surface is shown perpendicular to plane of incidence. Incoming light in the s polarization (which means perpendicular to plane of incidence - and so in this example becomes "parallel polarisation" to optic axis, thus is called extraordinary ray) sees a greater refractive index than light in the p polarization (which becomes ordinary ray because "perpendicular polarisation" to optic axis) and so s polarization ray is undergoing greater refraction on entering and exiting the crystal.$

$Doubly refracted image as seen through a calcite crystal, seen through a rotating polarizing filter illustrating the opposite polarization states of the two images.$

Comparison of positive and negative birefringence : In positive birefringence (figure 1), the ordinary ray (p-polarisation in this case w.r.t. magenta-coloured plane of incidence), perpendicular to optic axis A is the fast ray (F) while the extraordinary ray (s-polarisation in this case and parallel to optic axis A) is the slow ray (S). In negative birefringence (figure 2), it is the reverse.

View from under the Sky Pool, London with coloured fringes due to stress birefringence of partially polarised skylight through a circular polariser

Sandwiched in between crossed polarizers, clear polystyrene cutlery exhibits wavelength-dependent birefringence

Reflective twisted-nematic liquid-crystal display. Light reflected by the surface (6) (or coming from a backlight) is horizontally polarized (5) and passes through the liquid-crystal modulator (3) sandwiched in between transparent layers (2, 4) containing electrodes. Horizontally polarized light is blocked by the vertically oriented polarizer (1), except where its polarization has been rotated by the liquid crystal (3), appearing bright to the viewer.

Color pattern of a plastic box with "frozen in" mechanical stress placed between two crossed polarizers

Birefringent rutile observed in different polarizations using a rotating polarizer (or analyzer)

Surface of the allowed k vectors for a fixed frequency for a biaxial crystal (see ).

Birefringence is the optical property of a material having a refractive index that depends on the polarization and propagation direction of light.

$Refraction of light at the interface between two media of different refractive indices, with n2 > n1. Since the velocity is lower in the second medium (v2 < v1), the angle of refraction θ2 is less than the angle of incidence θ1; that is, the ray in the higher-index medium is closer to the normal.$

Snell's law

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A formula used to describe the relationship between the angles of incidence and refraction, when referring to light or other waves passing through a boundary between two different isotropic media, such as water, glass, or air.

$Reproduction of a page of Ibn Sahl's manuscript showing his discovery of the law of refraction.$

An 1837 view of the history of "the Law of the Sines"

$Wavefronts from a point source in the context of Snell's law. The region below the grey line has a higher index of refraction, and proportionally lower speed of light, than the region above it.$

$Light from medium 1, point Q, enters medium 2, refraction occurs, and reaches point P finally.$

$Demonstration of no refraction at angles greater than the critical angle.$

$Refraction of light at the interface between two media.$

In optics, the law is used in ray tracing to compute the angles of incidence or refraction, and in experimental optics to find the refractive index of a material.