What is Spontaneous emission: Definition and 32 Discussions

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. The first person to derive the rate of spontaneous emission accurately from first principles was 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.

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  1. S

    I Can there be some kind of photon emission caused by space expansion?

    Are there any kind of observed and experimentally verified processes or mechanisms where photon emission occurs and which are directly cause by spacetime expansion in some way?
  2. sol47739

    A Cause of spontaneous emission?

    I am reading this chapter 3 from the book called The Quantum Vacuum by P.Milonni.(Attached in the pdf, look at chapter 3.2 Spontaneous emission)There they say that spontaneous emission is due to both quantum fluctuations and radiation reaction. They say the transitions induced by the quantum...
  3. K

    I Confused about spontaneous emission

    Hello! I thought that in spontaneous emission (say for an atom with 2 energy levels) we have the electron in the excited state and then it decays to the ground state emitting a photon at the resonance frequency. However I saw the attached figure, which introduces Mollow triplet. I understand the...
  4. I

    I Relation between blackbody radiation and spontaneous emission

    I'm wondering what the relationship between blackbody radiation and spontaneous emission is. As far as I know, there are three sources of EM radiation - thermal radiation, oscillating dipole (multipole?), and LASER. And it seems like light emission from an atom can be separated into two...
  5. K

    B Can spontaneous emission be considered a thermodynamic process?

    I realize that nothing causes an excited atom to emit a photon, and that it's a random process. But someone was asking me about why energized systems in general tend to lose their energy to the environment and move toward equilibrium. I mentioned that an inflated balloon, given a hole, will tend...
  6. bhobba

    I Why Do We Have The Effect Of Spontaneous Emission And Absorption

    Hi All In another thread I answered was a question related to this and noticed another as well, so I thought I would give the full answer in its own thread rather than write it out twice. The other question has been deleted but here is the full detail anyway. First see...
  7. A

    I How does stimulated emission work in the process of light amplification?

    I understand the concept of stimulated emission and how it works as light amplification, but a certain technicality in its process eludes me. How is the inciting photon actually interacting with the electron that falls to a lower energy level? In every physical interaction that I know of there...
  8. L

    A Calculating the spontaneous emission rate for a material

    Hi, Suppose I have a 1D material of length L, and I want to calculate the spontanious emission rate Γ at ressonance frequeny. From my understanding, when light passes in a material at ressonance frequency it gets absorved by an electron in the atom, and after a spontaneous emission time tspont...
  9. X

    Laser pumping: further increasing injection above threshold?

    Above the threshold, the stimulation emission becomes dominant for lasing. If increasing the pumping, what will be the change of spontaneous emission and its contribution to the output power and FWHM of the signal, based on the threshold carrier density clamping and the threshold gain clamping...
  10. Spinnor

    B (N+1) enhancement of spontaneous emission, why not (N+1/2)

    Feynman tells us, "The probability that an atom will emit a photon into a particular final state is increased by the factor (n+1) if there are already n photons in that state." 4–4 Emission and absorption of photons, http://www.feynmanlectures.caltech.edu/III_04.html The 1 in (N+1) comes from...
  11. SchroedingersLion

    A Enhancing Spontaneous emission in a vacuum standing wave

    Hi, it is well known that spontaneous emission of an atom can be enhanced, if the atom sits at a node of the vacuum standing wave field in a cavity. My question is, why is it the node? At a node of a standing wave, there is zero intensity, so there should be no interaction between the atom and...
  12. T

    I Frustrated spontaneous emission

    I have heard of frustrated spontaneous emission that somehow says that an atom that normally emit light will cease to do so when its surroundings is incapable of absorbing light. How is this possible, and is this experimentally proven?
  13. G

    I Trying to understand how spontaneous emission works

    I'm reading Gerald Folland's "Quantum Field Theory: A Tourist Guide for Mathematicians" and I'm up to Section 6.2 which is called "A toy model for electrons in an atom". He has a nonrelativistic particle of mass M and a scalar field with quanta of mass m and the state space for the particle is...
  14. T

    A Do we need Lindblad operators to describe spontaneous emission

    In Griffith and Sakurai QM book, spontaneous emission is treated as a closed system subject to time-dependent perturbation. Yet in quantum optics sponantanoues emission is treated as in the form master equation of density matrix. Even in two levels system where there is only one spontaneous...
  15. Smalde

    I Spontaneous Absorption of Photons in Two State Quantum System

    Let's consider a two state quantum system in which an electron is either in the ground state or in the excited state with the energy difference E. We know that if we put this system in a monochromatic electromagnetic field (with frequency E/h) the electron can become excited by means of...
  16. G

    Solving the Mystery of Spontaneous Emission

    By Spontaneous emission it is said that the electron jumps to the higher energy state and then after some time "spontaneously" falls to the lower state. It is still not clear to me, what makes the electron to "fall" back to the lower state, if higher state is also allowed state and excitation...
  17. K

    Does Spontaneous Emission Affect Entropy Levels?

    Does entropy increase during spontaneous emission? If not, how is the information about the emitted photon mode encoded into the initial state of the atom (and/or environment)? If so, where does the extra information come from?
  18. G

    Excited state line width and thermodynamics

    I would appreciate very much if you could help me with a puzzling question that seems a paradox to me. Every excited state of an atom (every line of the characteristic spectrum) has a “width”: the higher the width, the shorter the lifetime of the state, and when the atom de-excitates we get...
  19. Q

    Problems of Spontaneous Emission, thanks.

    How to change the upper step to lower step on the figure? Why does N2(0) change to N2(t) the exp(-t/21) will be missed? Thanks.
  20. StevieTNZ

    Spontaneous Emission + Reversibility

    Hi there, In regards to the Spontaneous Emission of a photon from an atom, after that process occurs, is it possible according to the reversibility of the laws of Quantum Mechanics that the photon is re-absorbed by the atom? According to the reversible equation governing the process, would that...
  21. snoopies622

    Time until spontaneous emission in a QHO

    I have a quantum harmonic oscillator at energy level n_1, and I want to know how much time will pass before it spontaneously drops to energy level n_2. I know about the position operator, momentum operator, energy operator, and angular momentum operators. Is there a "time until a system...
  22. jaumzaum

    Photon of intermediary energy - Spontaneous Emission

    I'm studying spontaneous emission and I'm in trouble to understand the following: In a hydrogen atom we have distinct energy levels with different energy values associated to them. E1 = -13,6 eV E2 = -3,4 eV E3 = -1,51 eV To go from the first to the second energy level we need a photon...
  23. Q

    Spontaneous emission rates for two-level system

    Homework Statement Our quantum system has two levels: ψ1 = (1/\pi)1/4 * e-x2/2 ψ2 = (4/\pi)1/4 * x * e-x2/2 The energy of the ground state ψ1 is 0; the energy of the excited state ψ2 is \hbar * \omega0. What is the spontaneous emission rate for this system when it is in the excited state...
  24. M

    Understanding Atomic Dipoles and Spontaneous Emission

    Hi, In quantum optics, the interaction between light and atoms is described by a Hamiltonian of the form d.E where d is the dipole moment of the atom. The picture given is basically that this is a vector and we take the the dot product with this and the electric field vector (whose direction...
  25. F

    Spontaneous emission in photonic crystals

    Hello forum, I have a question about photonic crystals. From Wikipedia: "photons (behaving as waves) propagate through this structure - or not - depending on their wavelength. Wavelengths of light that are allowed to travel are known as modes, and groups of allowed modes form bands...
  26. F

    Relation between spontaneous emission, absorption and re-emission

    Hello Forum, when a wavefield is incident of an atom and the photon have the right energy (equal to the band gap energy), the photon is absorbed and disappear... But isn't the photon re-emitted later on and allowed to propagate through the material or does all its energy get lost into heat...
  27. K

    Does Einsteins coefficient for spontaneous emission depend on energy difference?

    Hi.. Does the Einstein's coefficient for spontaneous emission B depend upon the energy difference between the two levels?
  28. B

    Short question: Spontaneous emission from Feynman diagrams?

    Hey all, I am just wondering if one can directly calculate the Einstein coefficient in spontaneous emission of, say, two-level atoms through feynman diagrams? I searched for sources in google but could not find anything. Thanks a lot for an answer! Wit best regards, blue2script
  29. L

    Two photons spontaneous emission (2s->1s)

    Hi all, I'm doing a project that includes an hydrogen 2s->1s decay and I need the full derivation of this process, so if anyone can recommend about a book it would be great. I first thought it should be easy to find but to tell you the truth I have looked and found scratch. 10x a lot...
  30. T

    Life time in spontaneous emission for laser

    As we know, if we have a group of atoms at a moment N(t) in an exited state, it will exponentially decrease according to the relation: N(t)=N(0) exp(-At)=N(0) exp(-t/(tau)) Where A is the Einsteins constant for the spontaneos emission, In my book they defined tau in the relation I...
  31. F

    A thermodynamic approach to spontaneous emission

    any isolated macroscopic system, like a large group of atoms, always tends to reach a state that has the maxium entropy. if the electrons in this group of atoms are excited, they will give out their energy so that more degrees of freedom are activated, hence the entropy of the whole system...
  32. K

    Why Does an Excited Electron Decay to the Ground State?

    Can someone please explain why an excited electron in an atom decays to the ground state, if energy eigenstates are stationary states.