Questions tagged [photons]

The photon is the quantum of the electromagnetic four-potential, and therefore the massless bosonic particle associated with the electromagnetic force, commonly also called the "particle of light". Use this tag for questions about the quantum-mechanical understanding of light and/or electromagnetic interactions.

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What is the probability of QED interactions?

In Feynman diagrams of QED vertices of interaction are often labelled by the amplitude sqrt(alpha) where alpha is the e.m. fine structure constant. When higher order diagrams are constructed, each ...
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Why is a cell tower more dangerous than a stadium lights tower [closed]

Why a Wifi router with 100mW output power is suspected to be more dangerous (harmful for living things, perhaps has ionizing effect) than a 100W LED floodlight (assuming 50% efficiency of the LEDs ) ...
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Fundamental Limits for Photon Detection

In quantum electrodynamics "photons don't have positions". The physical relevance and consequences of this fact has been discussed on this site 1. (Further relevant questions about the concept of ...
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Why does adding a photon to the crystal of a semiconductor, gives a vertical transition in the reduced zone scheme?

Why does adding a photon to the system, gives a vertical transition in the reduced zone scheme? Considering me, it's due to the fact that a photon does not change de $k$-vector, is that correct? And ...
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Charge vs Mass in QFT: Photons vs Higgs-graviton “pair”

When we think about electric charge, one particle namely Photons is responsible of two important feature in particle physics: The property we call electric charge of an electron is statement about ...
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How to find the density of states from the dispersion relation numerically [closed]

I have a dispersion relationship as follows, (it is two-dimensional) $\omega=\sqrt{2 \frac{f}{m}\left[3-\cos k_{x} a-2 \cos \left(\frac{k_{x} a}{2}\right) \cdot \cos \left(\frac{\sqrt{3}}{2} k_{y} ...
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Does a single photon have a constant cross sectional energy? [closed]

A literal interpretation of the Planck-Einstein relation implies that a single photon has a constant cross sectional energy. The relation being $E=h\nu=hc/\lambda$ so a literal interpretation could be ...
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Converting matter into plasma using Sunlight?

How much light is needed to convert elements from a lower-state-of-matter such as from a solid directly to plasma without a liquid state, if that is possible?. Which element would produce the most ...
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How does electric and magnetic field interchanges in light propagation? [closed]

We know that magnetism is just a illusion created because of special relativistic effects and there is only electric field which is really there in reality. so how can we say that this imaginary ...
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Photon nonzero Spin (Helicity?)

I had a simple question - how many different values can a photon present for spin angular momentum, given that it's spin is 1? And although I immediately thought "3, since j = 2s + 1" (j being the ...
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How does photon addition (and subtraction) work?

Photon addition and subtraction are mathematically given by the creation and annihilation operators. $\hat{a}^{\dagger}|n\rangle=\sqrt{n+1}|n+1\rangle$ $\hat{a}|n\rangle=\sqrt{n}|n-1\rangle$ The ...
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If light is considered a wave, then what exactly is a photon? [duplicate]

So according to google: a photon is a particle that transmits light. Ok, but light is considered a wave, not a stream of particles(I'm pretty sure that this is what Young's double slit ...
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Linear Structure of Classical theory

I have been studying QFT from Timo Weigand’s lecture notes and in the chapter ‘Quantisation of spin-1 fields’, he describes the Feynman rules for QED and after some examples, there is subsection named ...
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Why does the photon have no antiparticle?

Considering the QED Lagrangian we get a solution of the form $A^{\mu}$. This solution has four degrees of freedom (dof). With the weak Lorenz gauge we reduce it to two dof. With this condition we also ...
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Can a chain reaction of photon->electron->photon->electron be possible?

Unless I'm wrong, I know that if a photon strikes an electron at the right frequency, the electron jumps to a higher energy orbit, and then comes back to its stable energy state. While coming back, it ...
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Entangled photons and CCD

Its a question about entangled pairs and double slit experiment. I have seen and read many such on the stackexchange but I can not really understand what is happening! So please don't stop the ...
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Does a 9,192,631,770 Hz hyperfine transition create 9,192,631,770 photons per second, or fewer?

I have read this question: Does an electron's drop from $2s$ to $1s$ produce the exact same type of photon in different atoms and molecules? where Emilio Pisanty says: Transitions which ...
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Why solids can produce a continuous light spectrum?

A textbook mentions: A bulb has a solid filament that is heated. Energy levels in solids overlap, so all energy changes for the electrons are allowed. This means the electrons can emit photons ...
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If you were to fire a laser or maser into space, how much of its energy would be lost to the atmosphere?

I'm very interested in knowing about how much energy would be lost to the atmosphere if you fired a laser or maser into space. I know the laser would probably diverge quite a bit over that distance, ...
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From a photon momentum perspective, why do dark surfaces absorb more heat?

We've all been taught that dark surfaces heat up faster, since they absorb photons, while light surfaces heat up slower, and reflect photons. But I can't reconcile this with momentum transfer. When a ...
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Rayleigh scattering and Raman scattering observed intensities

I am currently studying the textbook Infrared and Raman Spectroscopy, 2nd edition, by Peter Larkin. In a section entitled The Raman Scattering Process, the author says the following: Both Rayleigh ...
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How to hit / deflect a photon?

If you were trying to scatter a photon, what would be the best thing to try to fire at? Another photon? An electron? A proton? Does the energy of the thing I'm firing increase the probability of ...
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Photons absorbed by electrons, selections rule

I know that if a photon with a certain energy $E_1$ is absorbed by an electron, for example we are talking about Hydrogen atom, if this energy $E_1$ is equal to the difference in energy between two ...
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Is the interaction of the electron w/ a photon in the double-slit experiment simply distorts the experience & not the consciousness of the observer?

We know that in the Young double-slit experiment, the quantum interpretation of the experiment is based on the fact that an individual particle finds itself in a superimposed state following the ...
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What is the definition of spin for photon?

Massless particles, as the representations of the Poincare group, are characterized by helicity $h$ but people always say that photon has spin 1. What is the definition of spin for photon?
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Fast shutter to take image of photons [closed]

Let's guess there is a very sensitive photographic film so we can capture an image of each photon as a small black dot. Looking at photo of green light I can see $~2500$ photons per square meter. ...
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Higgs Field and its application [duplicate]

Today I was wondering about how elementary particle gets the mass. Well, you know that's the Higgs Field and we all know a lot about it. It is well known that more a elementary particle interacts ...
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If photon experiences time in an instant, does it mean that it's predestined to be consumed? [duplicate]

That one bothers me a lot. If time is collapsed to an instant for the photon, and it experiences it's own end of lifetime, what should happen if photon is never going to be absorbed? Especially ...
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Why does the earth and oceans emit primarily infrared photons?

Climate on earth depends a lot on infrared photons being emitted by the earth and its oceans. I want to know why the atoms in earth elements emit infrared photons after absorbing visible light, UV ...
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How do gravitons and photons interact?

First of all, I am a noob in physics (I‘m a computer scientist) and started reading Hawking‘s „A brief history of time“. In Chapter 6 he says that “electromagnetic force [...] interacts with ...
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How many photons are in a microwave oven?

I have always had trouble connecting the picture of classical electromagnetism with the idea of photons. To make this connection better I'd like to ask the following question. How many photons, at an ...
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Photoelectric effect v/s Compton effect

Whenever the bound electron is struck by a photon (as in photoelectric effect), then only the electron is emitted. But in Compton effect, when the bound electron is struck by a photon, then the entire ...
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Does a photon interact with the spin of an electron?

In optical transitions which involve collisions between photons (from light) and electrons present in a solid, say, the transition rate is typically given by Fermi's golden rule. But the equation ...
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Number of photons collected by a telescope [closed]

I’m trying to calculate how many photons of frequency $1420$ Mhz are collected by a telescope of area $100$ m$^2$ per second from the Andromeda Galaxy, which is 2 million light years away and has a ...
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Recoil velocity of atom after photon absorption

I'm trying to calculate the recoil velocity of a stationary atom after absorbing a photon, in terms of $E$ and $m$. I've tried manipulating relativistic equations, keeping in mind conservation of ...
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Is there some quantitative measurement or concept that can distinguish between a photon and a gluon?

Considering both photons and gluons have a mass of 0, a charge of 0, and a spin of 1, what distinguishes them? I want to exclude answers such as 'they influence different forces (i.e. photons are ...
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Detection of charged particle in optical fiber cable

There is a charged particle source and a light source attached to optical fiber cable which is attached to a light detector. Is it possible to detect the passage of a charge particle through the ...
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Do photons really have kinetic energy?

I haven't found a satisfactory answer to this question. In special theory of relativity $$E=\sqrt{m_{0}^2c^4 + p^2c^2}.$$ When we consider photons where $m_{0}=0$ then $E=pc$ but we also know that ...
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How does Teleportation based Error Correction (TEC) detect and correct loss/erasure errors?

I'm looking at papers like https://arxiv.org/pdf/1902.01692.pdf Page 10 and https://arxiv.org/pdf/1605.00527.pdf Page 3 and 4 and Figure 2. In all these, they mention that a QND measurement enables ...
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Do the Broglie's equation or the Higg's field could give “mass” to a photon?

I know that there are probably hundreds of questions about the mass of a photon, but none of those questions was able to clarify me some problems. I was talking with a guy on Facebook that says that ...
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What is the possibility for a gamma ray photon to pass through a composite particle like a proton?

As I know, the photon can be either absorbed or reflected from a particle, but as baryons or other hadrons are composite particles is there a defined possibility of passing through the volume inside ...
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Can high energy photons produce more photo current than a bit more intensity of photo electrons?

If we take 2 case : Case 1: Very high energy photons and a bit less intensity Case 2: less energy photons but a bit high of intensity In both case ,both energy of photons are greater than the ...
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Do photons form bound states?

Since photons do not have electric charge, they do not interact via the electromagnetic force. They are also reported to be devoid of any colour-charge, so interaction via the strong force is ruled ...
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A question about infinite energy

I know the conservation of energy doesn't allow that, and i saw a question on this forum about infinite energy: Why can't I do this to get infinite energy?, it says we can convert matter into ...
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How to explain light beams in terms of wave theory?

How can we explain the formation of light beams in terms of wave theory? According to wave theory, shouldn't the source point of beams emit radiation omnidirectionally, rather than a concentrated ...
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Was photon *defined* according to Standard Model *before* electroweak symmetry breaking ? Or were there only $W_3$ and $B$?

Was photon defined according to Standard Model theory before electroweak symmetry breaking ? Or were there only $W_3$ and $B$ ? Indeed, in Electroweak to Electro/Weak Bosons? Aman pawar answers "no" ...
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How come photons have no mass if they have energy and $E=mc^2$? [duplicate]

If photons have no mass, and yet have energy, how is that compatible with $E=mc^2$? Anything having mass should have energy (and the opposite should be true as well no)?
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Wavefunction of a photon

Does anyone have an explicit closed-form expression for the wavefunction of a single photon from a multipolar source propagating through free space? Any basis is acceptable as long as it is a single ...
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Why is there a concept of photons? Isn't it just EM waves at a certain wavelength?

Visible light is simply part of the EM spectrum at certain wavelengths. I assume UV and infrared don't even qualify as "photons". So why do we have this concept of a photon when all it is, is a ...
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What happens if a atom which can absorb a photon is placed behind a double slit?

Suppose there's an atom with an excited electron. So it will emit a photon at a definite frequency when the electron comes back from the excited state, which will spread like a spherical wave. Now if ...

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