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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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1answer
65 views

What are the quantum numbers of a photon?

For an electron we have $n$ (energy level), $m$ (orbital s p d f), $m_\ell$ (sub-orbital s px py pz d1 d2 d3 d4 d5 and the 7 f orbitals), $m_s$ (spin up or down with or opposed to the external ...
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1answer
33 views

Does a parabolic diffuse surface reflect more light than a flat, rectangular surface in 2D (see figure)?

Which surface reflects more light into the black collecting surface, considering both the light collecting surfaces have the same length? Is there an equation that could help me determine this? I'm ...
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2answers
135 views

Why does a photon have spin 1?

Are we taking the photon spin to be one to describe electromagnetic force or there is any equation (is it relativistic Schrodinger or Dirac equation?) with a solution that tells us that its value is ...
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1answer
21 views

Operation of a Laser Amplifier

I am very new to laser systems and have a quick question about the functionality of the amplifier. To my understanding, the amplifier serves to increase the energy of the incoming photons alongside ...
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1answer
17 views

Can X ray spectroscopy determine if a photon has left the lens of a camera?

I'm interested in knowing if you could measure a photon and see if it has left a material like silicon, which both the lens and CMOS sensor would contain. This wouldn't work if any nearby buildings ...
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2answers
132 views

Why isn't a quark-antiquark loop included in the photon self-energy corrections?

In QED, the Lagrangian has a term $\bar{\psi}A^\mu\psi$, which gives a correction to the photon propagator, where the loop is made of a pair electron-positron, with the 1st order diagram: In the ...
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1answer
42 views

Why do photons deposit their entire energy at a single point?

A version of the double slit experiment is done by firing single photons. It is possible that the fired photon could pass through either slit because of its small size. It is also possible that the ...
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2answers
32 views

At what point in space do we measure the electric field of an electromagnetic wave?

In an electromagnetic wave, the electric field varies in magnitude and direction. This electric field is at some point in space, point in the direction perpendicular to its velocity. See the image ...
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0answers
25 views

Minimum energy for pair production near charge $eZ$

According to the text "On the Production of the Positive Electron" by Oppenheimer and Plesset, from 1933, the authors give a lower bound for the energy $E$ for the pair production near a nucleus of ...
4
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1answer
72 views

Size of a single dot on a screen in a double-slit experiment

When a single photon hits a screen - it leaves a dot; and many dots of other photons later - an interference pattern emerges. My question is about size of a single dot. What are key factors varying ...
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2answers
18 views

How does the speed of light affect our cosmic observations/detections?

-I learned that if you look at a star 10 million lightyears away, the light that you are looking at is 10 million years old since the photons have been traveling at the speed of light for 10 million ...
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4answers
90 views

Gravitational interaction of two photons, initially separating [closed]

What would happen if two photons suddenly simultaneously appeared in empty universe and they would fly in different directions, one would go forward and second go upward. Since energy creates ...
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12answers
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If a photon truly goes through both slits (at the same time), then why can't we detect it at both slits (at the same time)?

I am not asking about whether the photon goes through both slits, or why. I am not asking whether the photon is delocalized as it travels in space, or why. I have read this question: Do we really ...
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0answers
16 views

Why is elastic scattering of photons (largely) non-isotropic, but inelastic scattering is isotropic?

I'm working on an experiment regarding Raman spectroscopy, and i'd like to fully understand the reasoning behind this fact. I assume it is related to the photons momentum. My apparatus has a '...
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1answer
27 views

Energy conservation when light reflects from mirror [duplicate]

Suppose we have a perfectly reflecting mirror which reflects 100% of the light incident on it. When a light beam falls on the mirror normal to the surface it will reflect in opposite direction from ...
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1answer
34 views

Help understanding unit: Micromoles per square meter per second

The context is light, illumnination, photons. The units seem to suggest something different from the definitions I have found: $$\frac{µmol}{m^2 s}$$ This, to me, says I have one millionth of a ...
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0answers
48 views

What's the farthest away from us a photon could theoretically reach?

Assuming the expansion of the universe will be dominated by dark matter, is there a limit to how far a photon could travel in terms of co-moving distance, as the Universe will be expanding faster than ...
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1answer
65 views

Is it possible to increase the orbital angular momentum (OAM) of a photon?

When the photon is emitted, can you change the angular speed? This has been experimented with vortex beams but I don’t quite understand how it works. Also, an optional follow up question, would a ...
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3answers
487 views

Where is the photon getting energy to deviate from its path?

If we make $\triangle$x really small, then in order to not break the Heisenberg uncertainty principle the photons will need to change momentum($\triangle$p), so where is it getting the energy to ...
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0answers
91 views

Probability of emitting a photon proportional to population in final state: problem with normalization?

In section 4-4 the Feynman Lectures reads: 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 ...
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2answers
51 views

Why doesn't an electron emit a photon when it absorbs one?

Obviously, an electron cannot emit a photon when it absorbs one (I think). An electron absorbs a photon of 1.8 eV, gets excited, emits another photon of 1.8 eV and falls back down to its ground state. ...
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2answers
92 views

Time and distance in a photon's frame of reference

Disclaimer, not a physicist. When I look at the sky I can see the star Rho Cassiopeiae. In my frame of reference, the photon hitting my retina has traveled for 4000 years and 3.78x10^16 km. In the ...
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1answer
78 views

Mathematical formalism to show that an atom casts a small shadow in the photon field that illuminate it

This questions regards the relationship between photon absorption and the spatial mode of light. In the question I have some physical intuition which I think I understand and which is born out by ...
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1answer
32 views

Which spin-1/2 photon states can be used in the context of Bell's inequality violations?

In textbooks, the violation of Bell's inequality is usually demonstrated for spin-1/2 systems in the state $$| \psi \rangle = \frac{1}{\sqrt{2}} \left( | +- \rangle - | -+ \rangle \right).$$ Most ...
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1answer
293 views

Do photons cast shadows

Large objects, for instance a tree, can cast shadows. Do elementary partices such as photos cast shadows. And can this be proven?
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Radiation pressure OAM

I have read this question: Where does the photon orbital angular momentum go in light-matter interactions? But the answers were not really explaining the photon level and the classical light level. ...
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2answers
69 views

Why the emitted photon has exactly the same energy,phase and direction as the incident photon in stimulated emission?

My textbook says:- When an atom emits a photon due to its interaction with a photon incident on it,the process is called stimulated emission.the emitted photon has exactly the same energy,phase and ...
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1answer
46 views

Can light of certain wavelengths stably orbit a black hole at the photon sphere?

I've recently learned that for a black hole, its photon sphere is an unstable orbit. Light either manages to escape from or fall into the event horizon, depending on how far away from the edge of the ...
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2answers
49 views

Can we charge a ray of light? Can photons never be charged under any circumstances? [closed]

can quantum theory never explain the hypothetical phenomena of charging photons? were there any experiments in this feild?
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3answers
82 views

What happens to the momenta of photons when light enters a medium

Light refracts as it enters a medium as the velocity decreases because the permittivity and permeability changes. So is there a change of momentum of a photon entering a refractive medium? And if ...
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1answer
106 views

The spin of light

The so-called spin is circular polarization of light,that is the electric field rotates in either direction normal to propagation Is it known or is there any theory about how fast the field rotates? ...
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0answers
19 views

How can I sample the solar spectrum to determine, in the vacuum of space, the frequency of a random photon?

I am working on improving a spacecraft charging model by simulating the photoelectric effect. To do so I need to determine the frequency of a random photon coming from the sun. How would I go about ...
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0answers
41 views

Einstein box : an entering photon

I was wondering if anyone considered a photon entering the Einstein-box, say because outside is 'hotter'. Would an increase in mass-energy be observable? Some may consider this a trivial question but ...
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1answer
39 views

Does light have its own mass? [duplicate]

If light has mass, then why don't we have light particles accumulated all over the earth?
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1answer
67 views

Maximum distance traveled by a photon up to the present time

What is the maximum distance and the maximum time a photon has traveled which is observed by us today at the particle horizon in the LCDM cosmological model applying general relativity?
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0answers
43 views

Linear dependence on photoelectric current

I have done a lab experiment in which we had to determine the Planck's constant through photoelectric effect. The equation reigning this experiment is: $$eV_c=h\nu-W$$ Where $\nu$ is the radiation ...
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2answers
74 views

How is it possible photons have no mass but have energy?

I know my question is so simple to ask but I'm new in this subject. I'm studying energy systems engineering in university and I took physics and advanced physics but I never truly understand how ...
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3answers
107 views

Photon and free fall

I have questions in 2 scenarios regarding this. Lets say according to an observer P at rest with respect to the earth, me & my friend start at the same time & at the same height to free fall ...
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3answers
1k views

Can a photon be split? [duplicate]

A photon is pure energy, zero mass. Different photons have different wave length and carry a different amount of energy. Now, it seems logical that a high energy photon can be split into 2 low energy ...
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3answers
125 views

Do photons oscillate or not?

This is not a duplicate. I am not asking about the connection between photons and EM waves nor wave particle duality. I have read these questions: What is the relation between electromagnetic wave ...
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1answer
43 views

How is reflection explained in quantum optics? [duplicate]

In classical electromagnetism, reflection is explained using the Maxwell equations and boundary conditions. How is reflection explained in quantum optics? What happens to photons during reflection? ...
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2answers
72 views

Can core electrons emit (visible) light?

I have read this question: https://physics.stackexchange.com/a/510012/132371 Where niels nielsen says: Furthermore, it is those outermost electrons that are responsible for giving color to some ...
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1answer
49 views

What observable(s) does a mirror operate on?

I'm reading this introduction to the Mach-Zehnder interferometer, and I'm confused about what the mirrors are doing. Suppose we're describing the path (upper / lower) and polarization (vertical / ...
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0answers
16 views

Thermodynamic limits to photovoltaic or photochemical processes

Photovoltaic or photochemical (photosynthesis) processes are basically extracting energy from the temperature difference between the Sun and Earth. In practice they are only able to capture photons in ...
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1answer
30 views

Interpretation of the photon scattering rate?

The photon scattering rate $\Gamma$ describes the rate at which photons scatter off an atom$^1$. In a two-level system, the ansatz for the photon scattering rate often is given by \begin{equation} \...
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1answer
81 views

Do all photons have the same proper time in different environment?

All photons have the same speed. In "space" (I mean when there is practically no matter) a photon will travel a distance faster than a photon in matter. But the speed is still the same. Do 2 photons ...
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2answers
60 views

Is there a connection between spontaneous symmetry breaking and massless photons?

I haven't studied a lot about these topics to put it that way. But I wonder if there is a connection between spontaneous symmetry breaking and the fact that photons are massless? The spontaneous ...
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0answers
28 views

Do sidebands corresponds to real photons at that frequency?

Say I have a carrier laser (optical) frequency $\omega_c$: $E=E_0 e^{i\omega_c t}$. I propagate it through an electro-optical modulator that modulates the phase by $\beta \sin\Omega t$: $E = E_0 e^{i\...
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0answers
30 views

Probability distribution for photon momentum in canonical ensemble

Suppose I have an ideal gas consisting of photons, each photon has an energy $\varepsilon = cp$ where $p = |\vec{p}| = \sqrt{p_x^2 + p_y^2 + p_z^2}$. I have calculated the single particle partition ...
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4answers
149 views

We all accept/believe in $c$. But what happens when light travels away from the center of gravity of a heavy star? Does it slow down?

I'm basically trying to understand a mysterious characteristic of the universe. Why light has to travel at $c$? I understand and accept that from experiment. Not arguing that it does not. Just saying ...