Questions tagged [photon-emission]

This tag is for questions regarding to Photon Emission. Photons are emitted by the action of charged particles, mainly due to making a transition from a high energy state to a lower energy state. Although they can be emitted by other methods including radioactive decay.

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At what wavelength do $\rm H_2$ molecules emission light if it is hit by electrons with 250 eV?

At what wavelength do $\rm H_2$ molecules emission light if it is hit by electrons with $250$ eV (electrons accelerated in a voltage of 250 V)? It's clear for atomic hydrogen - there is nowhere a jump ...
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Why do objects emit color even if they are not under the influence of heat?

Do correct me if I am wrong: I am assuming that, when you heat a material, say iron, the electrons gain thermal energy and jump to a higher energy level. When they fall back, they emit photons of ...
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Why is radiation of a particular frequency most intense in black body radiation?

Why is radiation of a particular frequency more intense than other frequencies in black body radiation? Does this mean that most electrons in the object are emitting photons of that frequency? If this ...
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Are photons really 'particles' of light? [duplicate]

In Einstein's Photon Theory of Light, he proposed that light consists of distinct chunks or distinct packets of energy called photon and the energy of a photon is given by : $E=hν$ where $ν$ is the ...
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Why does Hydrogen emit red light the most?

There are a lot of possible transitions that an electron can make in Hydrogen atom. So, a lot of possible wavelengths of light can be emitted. And among these, four are in visible light spectrum. But ...
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What would be the most UV resistant rubber color?

I'm looking for the longest lasting speargun bands. They come in a variety of colors so I'm wondering if a certain color of rubber would help them last longer. They will be exposed to a lot of ...
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What is the argument that Einstein's induced emission and induced absorption coefficients $B_{mn}=B_{nm}$ must be equal?

The following is a summary of my reading of https://www.feynmanlectures.caltech.edu/I_42.html#Ch42-S5 Defintions $N_{i}$ Population of molecules in state $i$ $R_{i\to j}$Transition rate from state $i$...
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How is light emitted by an incandescent lamp

I am looking for better understanding of how light is produced in an incadescent lamp. More specifically: how is the kinetic energy of electrons converted to light? Are we dealing with interband ...
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Feynman Lectures on Physics Vol-I 32-3 Radiation damping. How does this classical result relate to QM?

The following is from https://www.feynmanlectures.caltech.edu/I_32.html#Ch32-S3 Now let us actually calculate the Q of an atom that is emitting light—let us say a sodium atom. For a sodium atom, the ...
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Do the electrons in metastable state jump to ground state simultaneously?

Do the electrons, jumped from excited state at different times to the metastable state of gain medium, jump from metastable state to the ground state simultaneously or at different times which can or ...
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What causes neutrino thermal radiation?

Often in astrophysics, I see neutrino particles being considered as photons, in the sense that hot material emits neutrino thermal radiation. There are a lot of similarities of neutrino and photon ...
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Why is photon energy no function of transition time?

An electronic transition in an atom produces a photon, and the photon's energy is determined by the difference between upper and lower electronic state. For the final photon, its energy is described ...
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Can I burn a piece of wood by emitting only one photon per second on it?

Can I burn a piece of wood by emitting single photons on it? (for example by emitting only one photon per second or per milisecond etc to the wood). How much should be the rate of emitting single ...
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What are the lowest and highest energetic (electron shell) emission lines considering ANY molecule or atom (observed & theoretical)?

I am making this public interactive infographic of the electromagnetic spectrum on the web. In it I visualize all interactions of EM waves with matter. And I try to display boundaries for every ...
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How does absorption of light occur?

When photons hit matter, the electrons in that matter get excited (if the energy of the photon is sufficient to excite the electron to a higher energy state). But we know that the electrons are ...
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EM radiation fields from a single electron transition

This question is about a description for the EM fields created when an electron decays into a lower energy state spontaneously in a single, isolated atom. The treatment that I recall from grad school ...
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What is the difference between a radio antenna and a capacitor?

As I understand it, a mobile phone and a base station communicate by exchanging photons. The antenna is like one half of a capacitor. Pulsating voltage is applied to the conductive antenna and that ...
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How do we recognize 21cm emission line during Dark Ages

I was reading about the 21cm emission line of Hydrogen and its use to probe very different scale of redshifts, but something bothers me a little. How do you recognize an emission or absorption line ...
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What determines if a lamp produces emission or blackbody spectra?

If we take a lamp containing hydrogen gas and heat it up (gas-discharge lamp), it produces hydrogen's emission spectrum. Why doesn't it produce a blackbody spectrum? After all, the gas has some ...
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Is redshift acting on pulses from pulsars and how it changes the diffraction of the pulse and so its brightness?

Is redshift acting on pulses from pulsars and how it changes the diffraction of the pulse and so its brightness? As far as I know the diffraction becomes higher while wavelength increases as moving ...
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Full quantum model for spontaneous emission?

Often I hear it described that spontaneous emission is when vacuum fluctuations "kick" an atom and induce stimulated emission on its own, but I've never been able to find a convincing ...
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By how much does the gravitational redshift change a neutron star emission spectrum, thus disturbing the measurement of its surface temperature?

How much does the gravitational redshift change a neutron star emission spectra disturbing so the measurement of its surface temperature? I remember some tv-shows talking about Italian pasta when ...
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What happens to the non-axial photons of a laser cavity?

When a laser cavity is pumped, the axial photons are reflected back and forth by the cavity mirrors and so contribute to stimulated emission, but the non-axial photons do not have this opportunity. ...
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Why don't stars have emission lines? [duplicate]

I understand why stars have absorption lines, but I am not entirely sure why they don't have emission lines. Wouldn't the gas on the surface of the stars be hot enough to at least give off some ...
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Thermal radiation vs emission spectra of gases

I am a high school student and I am very confused in absorption and emission spectrum of gases, for e,g take hydrogen at room temperature for simplicity, so that we can talk in terms of Bohr's model ...
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Understanding the following THz-to-optical conversion scheme

When reading Real-time near-field terahertz imaging with atomic optical fluorescence. C. G. Wade, N. Šibalić, N. R. de Melo, J. M. Kondo, C. S. Adams & K. J. Weatherill. Nature Photonics 11, 40–...
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How to interpret the value of the Purcell factor?

I am a little bit confused regading the Purcell effect. If someone tells me that the Purcell factor of a system is 4? then does it means that the spontaneous emission is enhanced by 4 times the ...
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A question on maximum emitted power (Wien's law)

I'm new to radiative topics and when I came across spectral emissivity, this approach for maximum emissive power confuses me. The book normalize the emissive power using $$\frac{E_{b \lambda}}{n^{3} T^...
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Have anyone seen an unbound electron absorb/emit a photon via Bremsstrahlung process?

I know free electron cannot absorb or emit photon as it cannot satisfy both the conservation of energy and momentum at once but how about in Bremsstrahlung process? The presence of a positively ...
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Can inner electrons get excited? Can an already excited electron get excited again without first dropping to a lower energy level?

Is it only the valence electrons that can get excited or can the inner electrons get excited too? Plus, say for example can a electron of a hydrogen atom go from n=2 to n=3 without first returning to ...
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Relationship between the magnetic dipole of the electron and the polarisation of its radiation

When passing through a magnetic field, electrons are deflected sideways. This is the basis of the Lorentz force and all Hall effects. If this is done on a larger scale in particle accelerators or, in ...
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Is IR light emitted, rather than reflected?

When I look at an object in the sunlight, I'm looking at photons reflected back from the object. But if I wear infrared goggles and look at an object in the dark, am I looking at photons that are ...
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Why does spontaneous emission have larger spectral width than stimulated emission in a lasing medium?

What makes the stimulated emission's spectrum narrower than spontaneous emission's?
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If not fluorescence, what is the process of emission and absorption of white light by everyday objects?

An electron in an atom is excited by a photon and moves to a higher energy state. The electron then relaxes and transitions to a lower energy state emitting a photon of longer wavelength than that of ...
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Is it possible for a wavefunction to partially collpase?

What would happen in this situation: You have an ideal empty space with only two objects: a photon emitter, and a small observer. The emitter emits a photon in a random direction, with every direction ...
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Why do electrons in a cool gas not release photons as they are excited?

When white light is shone on a cool gas the electrons absorb photons of a certain wave lengths and become excited. Shouldn’t the electrons then return to ground and release photons with the same ...
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Random Direction of Spontaneous Emission, and Conservation Laws

I'm trying to imagine how/why the direction of a spontaneously emitted photon is random, and how that works and reconciles with the conservation of momentum and kinetic energy. For intuition, I was ...
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When can two electrons be excited in an atom?

In the National Institute of Standards and Technology's database, there is a table of the spectral lines produced by each atom in the periodic table https://physics.nist.gov/PhysRefData/Handbook/...
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Where do Photons in Hot “Box” Come From?

I've read through some related questions, like here, but these don't quite answer my question. Say I have an oven at room temperature, and I raise the temperature to 400 K. During this process, the ...
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Electron spin change and photon absorption/emission

I came across this document and would like to verify that I understand it correctly: My understanding is that only an electron with a negative electron spin can absorb a photon and thereby acquire a ...
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Why do we see a light “circle” in the Thomson Tube?

In the Thomson tube experiment, after the electrons have been accelerated, they enter a glass tube filled with a gas at low pressure. The tube is put between two coils that form a Helmholtz-coil. The ...
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Blackbody radiation vs spectroscopy

If a body (eg a metal) is glowing red hot then its temperature can be approximated solely based on the colour. But what if that colour is not due to blackbody radiation but due to excitation of ...
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Directionality of dipole radiation and spontaneous emission

I have a question on the directionality of the field radiated by an oscillating charge and the directionality of the spontaneous emission of say a two level atom. When I first started studying physics,...
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Why does the Sun's emission spectrum have missing lines? [duplicate]

I know it is because the electrons in hydrogen and helium absorb them however, they also drop back to ground state immediately and emit the previously absorbed photon. So there should be no net ...
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Why do photomultiplier tubes (PMT) require high voltage but silicon photomultipliers (SiPMs)/semiconductor photodiodes use low voltage for operation?

I have a PMT that requires 1000V for operation, but SiPMs, semiconductor photodiodes require only about 30V -- what fundamental feature causes this vast difference in operation bias?
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Is there an analogue to H-alpha emission in molecular hydrogen?

Balmer-alpha line emission in atomic hydrogen (i.e. H-alpha) corresponds to a wavelength of approximately 656 nm. As far as I can tell, in atomic deuterium, D-alpha emission is approximately the same ...
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How can energy conservation not be violated in stimulated emission processes?

Fermis golden rule, derived from time-dependent perturbation theory, give the rate for a quantum system, disturbed by a weak harmonic pertubation with frequency $\omega$, to transition from a state $|...
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Questions about sources of Infrared Radiation

Very simple question but I came across a website discussing sources of infrared radiation and it used an example to illustrate which objects emit more infrared than others. It said 'a candle flame ...
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In Franck-Hertz experiment, why mercury emits UV light while neon emits visible light despite neon having greater excitation energy?

The reference that I checked shows that Neon has an excitation energy of 18.2 eV, while mercury has 4.9 eV. However, the reference also shows that the wavelength emitted by the mercury is at the ...
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Balmer series for ionized lithium

I am trying to calculate the wavelength for the first spectral line in a Balmer-series for a two times ionized lithium, $\text{Li}^{2+}$. I know that the atomic number $z$ is 3 for lithium and it is ...

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