A report on Light and Wave–particle duality

A triangular prism dispersing a beam of white light. The longer wavelengths (red) and the shorter wavelengths (blue) are separated.

$Thomas Young's sketch of two-slit diffraction of waves, 1803$

The electromagnetic spectrum, with the visible portion highlighted

The photoelectric effect. Incoming photons on the left strike a metal plate (bottom), and eject electrons, depicted as flying off to the right.

Propagation of de Broglie waves in 1d—real part of the complex amplitude is blue, imaginary part is green. The probability (shown as the colour opacity) of finding the particle at a given point x is spread out like a waveform; there is no definite position of the particle. As the amplitude increases above zero the curvature decreases, so the amplitude decreases again, and vice versa—the result is an alternating amplitude: a wave. Top: Plane wave. Bottom: Wave packet.

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

Couder experiments, "materializing" the pilot wave model

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

Particle impacts make visible the interference pattern of waves.

Hong Kong illuminated by colourful artificial lighting.

A quantum particle is represented by a wave packet.

Interference of a quantum particle with itself.

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

Like all types of electromagnetic radiation, visible light propagates by massless elementary particles called photons that represents the quanta of electromagnetic field, and can be analyzed as both waves and particles.

- Light

Democritus (5th century BC) argued that all things in the universe, including light, are composed of indivisible sub-components.

- Wave–particle duality

4 related topics with Alpha

Photon

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Photoelectric effect: the emission of electrons from a metal plate caused by light quanta – photons.

The cone shows possible values of wave 4-vector of a photon. The "time" axis gives the angular frequency (rad⋅s−1) and the "space" axis represents the angular wavenumber (rad⋅m−1). Green and indigo represent left and right polarization

Thomas Young's double-slit experiment in 1801 showed that light can act as a wave, helping to invalidate early particle theories of light.

In 1900, Maxwell's theoretical model of light as oscillating electric and magnetic fields seemed complete. However, several observations could not be explained by any wave model of electromagnetic radiation, leading to the idea that light-energy was packaged into quanta described by . Later experiments showed that these light-quanta also carry momentum and, thus, can be considered particles: The photon concept was born, leading to a deeper understanding of the electric and magnetic fields themselves.

Up to 1923, most physicists were reluctant to accept that light itself was quantized. Instead, they tried to explain photon behaviour by quantizing only matter, as in the Bohr model of the hydrogen atom (shown here). Even though these semiclassical models were only a first approximation, they were accurate for simple systems and they led to quantum mechanics.

Photons in a Mach–Zehnder interferometer exhibit wave-like interference and particle-like detection at single-photon detectors.

Stimulated emission (in which photons "clone" themselves) was predicted by Einstein in his kinetic analysis, and led to the development of the laser. Einstein's derivation inspired further developments in the quantum treatment of light, which led to the statistical interpretation of quantum mechanics.

Different electromagnetic modes (such as those depicted here) can be treated as independent simple harmonic oscillators. A photon corresponds to a unit of energy E = hν in its electromagnetic mode.

A photon is an elementary particle that is a quantum of the electromagnetic field, including electromagnetic radiation such as light and radio waves, and the force carrier for the electromagnetic force.

Like all elementary particles, photons are currently best explained by quantum mechanics, and exhibit wave–particle duality, their behavior featuring properties of both waves and particles.

Electron

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Subatomic particle whose electric charge is negative one elementary charge.

A beam of electrons deflected in a circle by a magnetic field

The Bohr model of the atom, showing states of an electron with energy quantized by the number n. An electron dropping to a lower orbit emits a photon equal to the energy difference between the orbits.

In quantum mechanics, the behavior of an electron in an atom is described by an orbital, which is a probability distribution rather than an orbit. In the figure, the shading indicates the relative probability to "find" the electron, having the energy corresponding to the given quantum numbers, at that point.

Standard Model of elementary particles. The electron (symbol e) is on the left.

Example of an antisymmetric wave function for a quantum state of two identical fermions in a 1-dimensional box. If the particles swap position, the wave function inverts its sign.

A schematic depiction of virtual electron–positron pairs appearing at random near an electron (at lower left)

A particle with charge q (at left) is moving with velocity v through a magnetic field B that is oriented toward the viewer. For an electron, q is negative so it follows a curved trajectory toward the top.

Here, Bremsstrahlung is produced by an electron e deflected by the electric field of an atomic nucleus. The energy change E2 − E1 determines the frequency f of the emitted photon.

Probability densities for the first few hydrogen atom orbitals, seen in cross-section. The energy level of a bound electron determines the orbital it occupies, and the color reflects the probability of finding the electron at a given position.

A lightning discharge consists primarily of a flow of electrons. The electric potential needed for lightning can be generated by a triboelectric effect.

Lorentz factor as a function of velocity. It starts at value 1 and goes to infinity as v approaches c.

Pair production of an electron and positron, caused by the close approach of a photon with an atomic nucleus. The lightning symbol represents an exchange of a virtual photon, thus an electric force acts. The angle between the particles is very small.

An extended air shower generated by an energetic cosmic ray striking the Earth's atmosphere

Aurorae are mostly caused by energetic electrons precipitating into the atmosphere.

During a NASA wind tunnel test, a model of the Space Shuttle is targeted by a beam of electrons, simulating the effect of ionizing gases during re-entry.

Like all elementary particles, electrons exhibit properties of both particles and waves: They can collide with other particles and can be diffracted like light.

In his 1924 dissertation Recherches sur la théorie des quanta (Research on Quantum Theory), French physicist Louis de Broglie hypothesized that all matter can be represented as a de Broglie wave in the manner of light.

The emission of electrons from a metal plate caused by light quanta – photons.

Photoelectric effect

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Schematic of the experiment to demonstrate the photoelectric effect. Filtered, monochromatic light of a certain wavelength strikes the emitting electrode (E) inside a vacuum tube. The collector electrode (C) is biased to a voltage VC that can be set to attract the emitted electrons, when positive, or prevent any of them from reaching the collector when negative.

Diagram of the maximum kinetic energy as a function of the frequency of light on zinc.

The gold leaf electroscope to demonstrate the photoelectric effect. When the electroscope is negatively charged, there is an excess of electrons and the leaves are separated. If short wavelength, high-frequency light (such as ultraviolet light obtained from an arc lamp, or by burning magnesium, or by using an induction coil between zinc or cadmium terminals to produce sparking) shines on the cap, the electroscope discharges, and the leaves fall limp. If, however, the frequency of the light waves is below the threshold value for the cap, the leaves will not discharge, no matter how long one shines the light at the cap.

Angle-resolved photoemission spectroscopy (ARPES) experiment. Helium discharge lamp shines ultraviolet light onto the sample in ultra-high vacuum. Hemispherical electron analyzer measures the distribution of ejected electrons with respect to energy and momentum.

The photoelectric effect is the emission of electrons when electromagnetic radiation, such as light, hits a material.

Study of the photoelectric effect led to important steps in understanding the quantum nature of light and electrons and influenced the formation of the concept of wave–particle duality.

The interference of two waves. When in phase, the two lower waves create constructive interference (left), resulting in a wave of greater amplitude. When 180° out of phase, they create destructive interference (right).

Wave interference

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Phenomenon in which two waves combine by adding their displacement together at every single point in space and time, to form a resultant wave of greater, lower, or the same amplitude.

Interference of right traveling (green) and left traveling (blue) waves in Two-dimensional space, resulting in final (red) wave

Interference of waves from two point sources.

A magnified image of a coloured interference pattern in a soap film. The "black holes" are areas of almost total destructive interference (antiphase).

Geometrical arrangement for two plane wave interference

Interference fringes in overlapping plane waves

Optical interference between two point sources that have different wavelengths and separations of sources.

Creation of interference fringes by an optical flat on a reflective surface. Light rays from a monochromatic source pass through the glass and reflect off both the bottom surface of the flat and the supporting surface. The tiny gap between the surfaces means the two reflected rays have different path lengths. In addition the ray reflected from the bottom plate undergoes a 180° phase reversal. As a result, at locations (a) where the path difference is an odd multiple of λ/2, the waves reinforce. At locations (b) where the path difference is an even multiple of λ/2 the waves cancel. Since the gap between the surfaces varies slightly in width at different points, a series of alternating bright and dark bands, interference fringes, are seen.

White light interference in a soap bubble. The iridescence is due to thin-film interference.

The Very Large Array, an interferometric array formed from many smaller telescopes, like many larger radio telescopes.

Interference effects can be observed with all types of waves, for example, light, radio, acoustic, surface water waves, gravity waves, or matter waves.

Light can be explained classically by the superposition of waves, however a deeper understanding of light interference requires knowledge of wave-particle duality of light which is due to quantum mechanics.