What is Stimulated emission: Definition and 50 Discussions

Stimulated emission is the process by which an incoming photon of a specific frequency can interact with an excited atomic electron (or other excited molecular state), causing it to drop to a lower energy level. The liberated energy transfers to the electromagnetic field, creating a new photon with a phase, frequency, polarization, and direction of travel that are all identical to the photons of the incident wave. This is in contrast to spontaneous emission, which occurs at random intervals without regard to the ambient electromagnetic field.
The process is identical in form to atomic absorption in which the energy of an absorbed photon causes an identical but opposite atomic transition: from the lower level to a higher energy level. In normal media at thermal equilibrium, absorption exceeds stimulated emission because there are more electrons in the lower energy states than in the higher energy states. However, when a population inversion is present, the rate of stimulated emission exceeds that of absorption, and a net optical amplification can be achieved. Such a gain medium, along with an optical resonator, is at the heart of a laser or maser.
Lacking a feedback mechanism, laser amplifiers and superluminescent sources also function on the basis of stimulated emission.

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  1. RobbyQ

    I Stimulated Emission & Emitted photon direction

    I always understood that a photon of correct wavelength would raise the energy level of an electron (which is the case) But reading about lasers and stimulated emission I read the following where the electron drops a level upon absorption:- "A photon with the correct wavelength to be absorbed by...
  2. JD23

    A Stimulated emission/absorption - which equations act on external targets?

    Stimulated emission-absorption have two symmetric equations for population (N_1 - number of ground state atoms, N_2 - of excited) written below, at heart of lasers: https://en.wikipedia.org/wiki/Stimulated_emission#Mathematical_model We assume that both equations act on the central target inside...
  3. dbabic

    A Spontaneous and stimulated emission in Planck's radiation law

    Hello, Einstein introduced stimulated emission (along with spontaneous emission and absorption) to derive Planck's radiation law using his A and B coefficients in his 1917 paper. My question is, is it possible to separate the Planck radiation spectrum into a fraction that is spontaneous...
  4. K

    I Stimulated emission in harmonic oscillator

    Hello! Is stimulated emission possible for a harmonic oscillator (HO) i.e. you send a quanta of light at the right energy, and you end up with 2 quantas and the HO one energy level lower (as you would have in a 2 level system, like an atom)?
  5. R

    I Qualitative description of stimulated emission & population inversion

    I'm having trouble understanding stimulated emission and population inversion, and how they work together to make a laser work. I pretty much need this explained completely. 1. Spontaneous emission, they say, is when an atom absorbs and then later emits a photon. Isn't that just regular...
  6. J

    I Are all processes CPT symmetric like measurement, stimulated emission?

    https://en.wikipedia.org/wiki/CPT_symmetry says "CPT theorem says that CPT symmetry holds for all physical phenomena" - e.g. we could imagine decomposition of given phenomena into Feynman diagrams and apply CPT symmetry to all of them. However, for some o processes such reversibility seems...
  7. Erik Ayer

    I Polarization and Stimulated Emission

    If a laser beam has a definite diagonal polarization, it is in a superposition of horizontal and vertical polarization. If that beam were then sent through another lasing medium and caused stimulated emission of another photon (or possibly several photons), would those be in superposition...
  8. Erik Ayer

    I Mach-Zehnder with Stimulated Emission

    Imagine a Mach-Zehnder interferometer adjusted so that light comes out one face of the final beam splitter, as per normal use. In the arms, lasing material is added so that photons can cause stimulated emission of more photons that should be the same wavelength and in phase - they should be...
  9. N

    Does radioactive decay exhibit stimulated emission?

    If you have a lump of the same species of radioactive isotopes, why can't the photons emitted from the radioactive decay of one nucleus cause spontaneous emission from other atoms? I presume it doesn't, because if it did, there would be a geometric effect of radioactive decay, which is not...
  10. DaTario

    A Increase of coherent length in stimulated emission

    Hi All, When I teach the basic structure of a laser setup, stimulated emission appears as a fundamental phenomenon. But in no reference I found a description that could account for the increase of coherent length of the EM laser field. According to my knowledge, one photon typically doesn't...
  11. B

    Photoelectric Effect versus Laser Stimulated Emission [Confused]

    Our teacher taught us "Laser" today and it made me confused. So Electron s energy in n=1 is around 13 eV (-13eV) and in n=2 is around -3.4 eV. Our teacher told us if we radiate a photon which has 9.6 eV energy (the difference energy of the first and second layer, n1 and n2, which is 13-3.4=9.6...
  12. 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...
  13. F

    I What Happens When Photon Energy Differs in Stimulated Emission?

    Please teach me: if stimulate photons have energy different from the difference of two energy levels of atom then what is happened?What is coefficent of the stimulate emission in this case?
  14. P

    Stimulated emission per second per atom?

    Homework Statement We are investigating hydrogen in a plasma with the temperature 4500 ºC. Calculate the probability per atom and second for stimulated emission from 2p to 1s if the lifetime of 2p is 1.6 ns Homework Equations Planks radiation law: ##\rho (f) = \frac{8* \pi...
  15. P

    Probability per atom and per second for stimulated emission to occur

    Homework Statement We are investigating hydrogen in a plasma with the temperature 4500 ºC. Calculate the probability per atom and second for stimulated emission from 2p to 1s if the lifetime of 2p is 1.6 ns Homework Equations ##A=\frac{1}{\Sigma \tau}## $$A_{2,1} = \frac{8*\pi *h *...
  16. 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...
  17. S

    A Semi Classical Explanation of Stimulated Emission

    Can Stimulated Emission in lasers be explained semi classically? If so, how?
  18. physics loverq

    B What is the underlying reason for stimulated emission?

    I learned that stimulated absorption, spontaneous emission and stimulated emission are three fundamental concepts in the process of radiation. Among these three concepts, I found stimulated emission really hard to comprehend, it says when atom in its excited state is stimulated by external...
  19. S

    B Why do photons stimulate emission in atoms?

    I can't get my head around stimulated emission.Why does a photon traveling towards an atom stimulate emission? The best way I could answer is that a photon has an electro magnetic field and this causes an excited atom to oscillate.This induces an excited electrons to fall down an orbital. But...
  20. E

    I What's the interval between photons in stimulated emission?

    What's the interval between photons in stimulated emission? In stimulated emission one photon induces the emission of a second photon whose coherence length, energy, polarisation and direction of travel are all identical to its own. There must be a delay between the two photons, see below, so...
  21. EspressoDan

    Light - Black-bodies & Spontaneous / Stimulated Emission.

    Hello, I have a short question: In relation to the Sun - is Black-body radiation ultimately the result of a combination of spontaneous (majority) and stimulated (minority) emission of photons? In relation to the IR emissions from everyday objects due to their temperature - is Black-body...
  22. Karolus

    B What is the fundamental principle behind the operation of a laser?

    The principle of operation of the laser is based on stimulated emission concept. In short, if a suitable energy photon hits the electron of an atom, in which the electron is in the excited state, there is a probability that the electron returns to the ground state. The photon emitted has the...
  23. T

    A Difference between ASE and stimulated emission

    Is there any inherent difference between amplified spontaneous emission and stimulated emission? Is not stimulated emission simply the mechanism by which ASE occurs? Is stimulated emission just a broader term? I've read the two terms in literature and just wanted to ensure I understood the...
  24. E

    I Planck formula and density of photons

    Hello! Let's consider again a system of atoms with only two permitted energy levels E_1 and E_2 > E_1. When electrons decay from E_2 level to E_1, they generate a photon of energy E_{21} = E_2 - E_1 = h \nu. The number of photons (per unit frequency, per unit volume) emitted by such a system in...
  25. TheOfficialAB

    LASERs: Why is population inversion required for amplification?

    Hi, I'm doing a module on quantum optics and lasers. Most of the texts and online source I have read simply state that 'population inversion is essential for amplification in laser operation'. My question is, why? Amplification/Gain is essentially the result of stimulated emission. Can't...
  26. D

    Stimulated Emission: Is this how we see images?

    I got the explanation about stimulated emission and lasers as explained here: Understanding Stimulated Emission: Got the what, how about the why? What I'm still unsure about is if this also explains the simpler question of how light passes through a transparent medium, like glass, yet the...
  27. Erik Ayer

    Stimulated emission and polarization - a thought experiment

    Imagine that one has a single photon of 632nm. It enters the back end of an open-ended HeNe laser tube - one with no mirrors - and along its path, causes the emission of another photon. According to the wikipedia entry on stimulated emission (https://en.wikipedia.org/wiki/Stimulated_emission)...
  28. M

    Semi-classical argument for stimulated emission?

    Laser action by definition requires the presence of stimulated emission in the laser medium. The typical way of treating this semi-classically is to introduce the Einstein coefficients, in essentially an ad hoc way, then derive the Einstein equations for the various level population transitions...
  29. Alastair McD

    Can stimulated emissions from CO2 be absorbed?

    When an excited molecule absorbs a photon two coherent photons are emitted. If one of these photons is absorbed by a second molecule, since the emission was coherent then that molecule will absorb the second photon too. If the second molecule was in the ground state then it will become excited...
  30. G

    No-cloning and stimulated emission

    Hi, I'm trying to find out why stimulated emission (creation of an identical photon) doesn't violate the no-cloning theorem. There are lots of different opinions on this on the internet, e.g. "the second photon is not exactly identical, the energy is slightly different" or "since stimulated...
  31. Z

    Stimulated Emission = Stimulated Absorption

    I'm having a bit of trouble understanding this. I am going through the section in Griffith's regarding Einstein's Coefficients. For a system in equilibrium, the rate of particles undergoing emission needs to equal the rate of particles undergoing absorption in order to maintain equilibrium...
  32. W

    How does stimulated emission occur in lasers?

    I was reading about LASER production when I came by the concept of stimulated emission. The book I was reading doesn't elaborate the topic much,so far I have understood what stimulated emission is but not how it happens. When a photon strikes an excited atom the atom falls to it's ground state...
  33. Shailesh Pincha

    Stimulated Emission: De-exciting Electrons with Photons

    How is a photon responsible for de-excitation of an electron in higher energy state?
  34. Y

    What causes stimulated emission to occur in quantum mechanics?

    I have been learning some introductory quantum mechanics and stimulated Emission is giving me some problems conceptually. I understand that photons can be absorbed to bump electrons up to higher energy levels and that electrons in the higher energy state spontaneously decay back to the lower...
  35. A

    Why don't electron go into the next orbit during stimulated emission?

    Why don't electrons go into the next orbit during stimulated emission? Hey all, I was studying stimulated emission in lasers and I had a doubt regarding the same. When the electron collides with another which is in an excited state, why doesn't the electron, which gets collided, move into the...
  36. B

    Stimulated Emission: Understanding Its Changing Rate

    I am having trouble understand why is true I would think that the rate in which N2 is changing is the rate of stimulated emission and spontanous emission together. Why is it just the rate of stimulated emission It is in the mathematical model section...
  37. C

    Spontaneous vs Stimulated Emission

    Hi! I wanted to check if I have got the correct interpretation of stimulated vs spontaneous emission. It seems like stimulated emission is defined as a process for which an excited atom/electron spontaneously relaxes down to a lower energy level. Stimulated emission on the other hand...
  38. T

    Stimulated Emission has no sufficient proof?

    Hi All I was surfing Internet trying to understand why most books i read simply considers that the stimulated photon emission has same properties as the stimulating photon, and treats this simply as an "take as it is". For my surprise, i found this article...
  39. N

    Textbook tries to argue stimulated emission from boson behaviour?

    Hello, "Quantum Mechanics" by Basdevant and Dalibard tries to qualitatively deduce stimulated emission of atoms shined upon with some light by using Bose Einstein statistics. Imagine a certain photon in eigenstate n and if we turn on a potential v temporarily, the chance of it ending up in...
  40. lonewolf219

    Stimulated Emission by Laser discussion

    I'm doing a very short presentation on a laser. I want to discuss the most important concepts of a laser (in less than ten minutes). What should I include? I was thinking about stimulated emission and amplification. (But I'm not sure I really grasp these concepts) For instance, does...
  41. L

    Laser action and stimulated emission

    Homework Statement Revered Members, An electron in ground state makes its way to an excited state upon absorption of photon of energy, equivalent to energy difference between ground state and excited state, and after some time, it decays by emitting the photon and returns to the ground...
  42. F

    Understanding Stimulated Emission: Got the what, how about the why?

    I've read the literature on the matter, but I'm still not entirely clear what's going on. The general idea I'm getting is: "You have a photon and an excited atom, photon comes near atom, stuff happens, and now you have two (identical) photons, also identical to the first, and traveling in the...
  43. A

    In stimulated emission how does the incident photon make release of

    In stimulated emission how does the incident photon make release of other photon from another atom? advanced thanks.
  44. A

    Can you explain the phenomenon of stimulated emission in lasers?

    I am interested in learning the nature of the interaction between a photon and the atoms in a medium that has undergone population inversion that causes stimulated emission i.e. if an excited-state atom is perturbed by a photon (with an electric field of specific frequency), why does it emit an...
  45. V

    Gas Laser: Stimulated Emission and Positive Ions

    In a gas laser, an electron in the highest energy state absorbs photon for stimulated emission to occur, but now since it has more energy than its highest state, shouldn't it escape the atom and the active medium be left only with positive ions?
  46. S

    Stimulated Emission: Why Are Photons In Phase?

    Hi. I can't see why the photon created by stimulated emission in a common laser should be in phase and with the same polarization of the original photon. Thank you.
  47. S

    Stimulated Emission: Intuitive Explanation Needed

    I am trying to find an intuitive explanation for the stimulated emission phenomenon. I know the effect: a photon with the right frequency "interacts" with an excited electron to create a copy of itself( same phase, same amplitude, same state) putting the electron to a lower energy state... But...
  48. E

    Units for Einstein coefficients in stimulated emission?

    Homework Statement Hi, I need to know the correct SI units for Einstein Coefficients (A and B) for stimulated emission (say laser). The equation I'm on about is Homework Equations \frac{A}{B} = \frac{8\pi h\nu^{3}}{c^{3}}The Attempt at a Solution after some scribbling I got to \frac{A}{B}...
  49. F

    Do spontaneous and stimulated emission obey to a Boltzmann's statistics ?

    Are spontaneous and stimulated emission selected by a Boltzmann's statistics ? Consider 2 levels(m,n) oscillators in thermal equilibrium with Einstein's coefficients Amn (spontaneous emission), Bmn (stimulated emission), Bnm (absorption) and r(f) the energy density at the frequency f (black...
  50. deccard

    Stimulated emission. Energy of the photon inducing the emission.

    In order to produce stimulated emission we need a photon which has the same energy as the difference is the lower and upper energy levels in the excited atom. But how exactly the energy of the photon does have to correspond to the energy difference between the levels. Can stimulated emission...