Spontaneous emission is the process in which a quantum mechanical system (such as a molecule, an atom or a subatomic particle) transits from an excited energy state to a lower energy state (e.g., its ground state) and emits a quantized amount of energy in the form of a photon. Spontaneous emission is ultimately responsible for most of the light we see all around us; it is so ubiquitous that there are many names given to what is essentially the same process. If atoms (or molecules) are excited by some means other than heating, the spontaneous emission is called luminescence. For example, fireflies are luminescent. And there are different forms of luminescence depending on how excited atoms are produced (electroluminescence, chemiluminescence etc.). If the excitation is affected by the absorption of radiation the spontaneous emission is called fluorescence. Sometimes molecules have a metastable level and continue to fluoresce long after the exciting radiation is turned off; this is called phosphorescence. Figurines that glow in the dark are phosphorescent. Lasers start via spontaneous emission, then during continuous operation work by stimulated emission. Spontaneous emission cannot be explained by classical electromagnetic theory and is fundamentally a quantum process. According to the American Physical Society, the first person to correctly predict the phenomenon of spontaneous emission was Albert Einstein in a series of papers starting in 1916, culminating in what is now called the Einstein A Coefficient. Einstein's quantum theory of radiation anticipated ideas later expressed in quantum electrodynamics and quantum optics by several decades. Later, after the formal discovery of quantum mechanics in 1926, the rate of spontaneous emission was accurately described from first principles by Dirac in his quantum theory of radiation, the precursor to the theory which he later called quantum electrodynamics. Contemporary physicists, when asked to give a physical explanation for spontaneous emission, generally invoke the zero-point energy of the electromagnetic field. In 1963, the Jaynes–Cummings model was developed describing the system of a two-level atom interacting with a quantized field mode (i.e. the vacuum) within an optical cavity. It gave the nonintuitive prediction that the rate of spontaneous emission could be controlled depending on the boundary conditions of the surrounding vacuum field. These experiments gave rise to cavity quantum electrodynamics (CQED), the study of effects of mirrors and cavities on radiative corrections. (Wikipedia).
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From playlist Preliminary Chemistry - Energy
137 - Stimulate Emission In this video Paul Andersen explains how stimulated emission can be used to create coherent light. When an atom absorbs a photon it moves to a higher energy level through stimulated absorption. It may then release a photon and moves to a lower energy level throu
From playlist AP Physics 2 Videos
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From playlist Chemistry
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From playlist 04. Chemistry and Physics
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From playlist Optoelectronic and Photonic Devices
The physics of a laser - how it works. How the atom interacts with light. I’ll use this knowledge to simulate a working laser. We will learn how LASERs relies on Stimulated absorption, Spontaneous emission, and most importantly: Stimulated Emission- This last type interacts with an excite
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From playlist Chemical Reactions and Stoichiometry
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From playlist Optoelectronic and Photonic Devices
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From playlist Optoelectronic and Photonic Devices
14. Atom-light Interactions III
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From playlist MIT 8.421 Atomic and Optical Physics I, Spring 2014
LASER Below Threshold Explained
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From playlist Optoelectronic and Photonic Devices
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From playlist Optoelectronic and Photonic Devices
15. Atom-light Interactions IV
MIT 8.421 Atomic and Optical Physics I, Spring 2014 View the complete course: http://ocw.mit.edu/8-421S14 Instructor: Wolfgang Ketterle In this lecture, the professor first reviewed Einstein's A and B coefficients and spontaneous emission, then discussed degeneracy factors, fully quantize
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From playlist MIT 8.421 Atomic and Optical Physics I, Spring 2014
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