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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Why is UV radiation below 200nm strongly absorbed by Oxygen?

According to https://en.wikipedia.org/wiki/Ultraviolet#Subtypes Ultraviolet radiation below $200$ nm is considered to be Vacuum Ultraviolet, due to being strongly absorbed by atmospheric Oxygen. ...
blademan9999's user avatar
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What information is gained when just one single half of an entangled photon pair is detected, following its transmission through a polarizer?

My admittedly limited understanding of QM is that it is a matter of probabilities whether or not a photon is (re)transmitted through a polarising filter and that these are a function of the relative ...
tonyess's user avatar
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Equivalent mass enhanced inside dielectric (modified Rohrlich)?

I shall modify an argument for energy-mass equivalence due to Fritz Rohrlich to be valid inside a dielectric medium with refractive index $n$ and light velocity $c_n=c/n$. (Alternative argument to the ...
John Eastmond's user avatar
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What is the minimum energy needed for the photodisintegration of U-238?

What is the minimum threshold energy needed for a photon to cause photodisintegration in Uranium 238, and how different (in terms of MeV) is this energy needed for photodisintegration from the energy ...
Young Jun Lee's user avatar
1 vote
2 answers
115 views

Why PN junction is needed to detect photons

I am very new to semiconductors and I'm trying to understand how photodiodes work for imaging sensors. If I am not wrong, a PN junction is required to detect electron/hole pairs that are photo-...
bruno's user avatar
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Optical Tweezers in a Vacuum | Oscillation

In the context of optical tweezers, if used in a vacuum and a particle starts off slightly to the right from the center of a beam, would the particle eventually become perfectly centered or would it ...
vxnuaj's user avatar
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7 answers
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Relativistic time dilation and the biological process of aging

Although I understand many of the "thought experiments" which demonstrate how simple clocks slow down (when moving) as result of the constancy of light speed postulate, I find it hard to ...
user2554's user avatar
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Equivalent mass enhanced inside dielectric medium?

Imagine a box of mass $M$ and length $L$ containing a medium with refractive index $n$. A photon is emitted from the left-hand side of the box and is absorbed on the right-hand side. Let us assume ...
John Eastmond's user avatar
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Relationship between Current and Stopping Potential in the photoelectric experiment

Is there a way to form an equation for the graph of Current against Stopping Potential for the photoelectric experiment? If so, how?
john's user avatar
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Photon radiation from condensing water

Does water vapor generate electromagnetic radiation/photons when it condenses into water droplets? I know that gas water molecules need a condensation particle to combine into water droplets. A pair ...
Paul in Boston's user avatar
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Why is the second-order correlation function proportional to the population of the excited state?

In this paper (click to open it) A. Beveratos et al., 'Bunching and antibunching from single NV color centers in diamond' the authors write the following equation (page 4, eq. 1.2): Namely, they ...
DrManhattan's user avatar
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What is the reason why quantum mechanics is said to be "probabilistic"? [duplicate]

I know that perhaps some will answer with "the double slit experiment" but what is it that makes the double slit experiment something probabilistic? I cannot understand this and please I ask ...
Etherealist's user avatar
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Do the results of the Elitzur-Vaidman quantum bomb tester experiment imply that counterfactual events affect what is observed?

Assuming that light travels as photons that can interfere with themselves while also only being detected as specific localized points, the results of the Elitzur-Vaidman quantum bomb tester experiment ...
OneStrangeQuark's user avatar
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1 answer
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Why does the following formula stands for photon number conservation?

I'm reading some materials(before eq(129)) about beam splitters while I met the following formula $$ \hat a_{\mathrm{in}}^{\dagger}\hat a_{\mathrm{in}}+\hat b_{\mathrm{in}}^{\dagger}\hat b_{\mathrm{in}...
narip's user avatar
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Why does a single-photon avalanche diode (SPAD) need to be a diode?

Exactly what the title asks. "Diode" comes with it the ideas of depletion layers and forward/reverse biasing and electron-hole recombination, but SPAD physics doesn't seem to be dependent on ...
flevinBombastus's user avatar
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What is the Hilbert space of a single photon?

I'm trying to understand the second quantization of photons. Following expression (4.3.5) in the lecture note:Second Quantization, a Hilbert space of a indistinguishable multiparticle system in second ...
Fieldx's user avatar
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If you measured the electric field of a photon, would the value be constant in magnitude over time?

Because photons have varying probabilities of having angular momentum ℏ and -ℏ (depending on polarization), it doesn't seem like there's a true "linear" polarization. Instead with linearly ...
WaveInPlace's user avatar
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3 answers
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"Artificially" time dilated photons

If you bang on the table you create a single thump, but if you keep doing so with shorter and shorter intervals, eventually it'll start to sound like a note with a particular pitch. Now, if I used a ...
Cosmo's user avatar
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How do beam splitters work?

My main three questions are: 1.) What is the physical phenomenon that occurs in the interaction between a beam of light and a beam splitter that results in two beams of specific proportions of the ...
OneStrangeQuark's user avatar
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1 answer
191 views

Was doppler effect for light proven experimentally?

If so, provide me with the data sources. From what I read, doppler for light is taken for granted. Or sometimes based on theoretical formulas. But if one wants to theorise, light is a mix of photons ...
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Massive equivalent of a photon and deduction of a photon's linear momentum

Since photons have an energy given by $E=h\nu$, we could define a particle whose rest mass is such that it has the same energy than the photon: $E=m_0c^2 \Longrightarrow m_0=\frac{h\nu}{c^2}$. We now ...
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How long until light reaches me if I travel away from a point? [closed]

Let's assume that: I'm 1 light year away from some point in space I'm travelling away from that point at 0.5c (or whatever fraction of the speed of light it takes for relativity to play a big role) A ...
Jabrove's user avatar
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6 votes
6 answers
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Newtonian light deflection

It is often stated that the light deflection by a point mass $M$ of a photon passing within distance $b$ is according to Newton $$ \theta = \frac{2GM}{bc^2}, $$ which is exactly half the value ...
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Interferometer with widely varying pathlengths - and a pulsed laser souce

I'm trying to understand the nature of the wavefunction within an interferometer as described below, so I can make accurate predictions about it's behavior. The experiment goes like this. A laser ...
CovetingSurface's user avatar
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1 answer
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Can light photons have shape of a leaf? [closed]

Can light photons be in the shape of a leaf ,so that when they hit a vertical polariser, they start waving in the vertical direction and vice versa .
Varun Sharma's user avatar
3 votes
3 answers
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Photon collison with an atom

I'm currently studying atomic physics and have encountered a topic that I find challenging. My question is regarding the collision between a photon with an energy of, let's say, 12.20 eV and an atom. ...
exo's user avatar
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3 answers
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QED photon path (direction of photon emission)

In QED we look at all possible path a photon could go from S to P, and I understand the most significant contributions to the final arrow are the few near straight paths connecting S and P while other ...
ABC's user avatar
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Inverse square law of a photon in QED

So in Feynman's QED book strange theory of light and matter, he mentioned as a photon travels, it spreads a little, thus the "arrow" shrinks inversely with distance, and that is the inverse ...
ABC's user avatar
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Gravitational Effect on Photon [duplicate]

It is known that photons are massless particles. So why is light affected by the strong gravitational field of black holes?
Skynet's user avatar
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1 answer
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Choice of complex photon polarization vector

Given a complex photon polarization vector, can I always choose a Lorentz frame and gauge in which it is real?
Len's user avatar
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Is there a natural limit to the frequency of a pendulum swing near a black hole, and does this imply the same for photons? [closed]

I imagine a swinging pendulum being held outside a black hole supported by the normal foce of a jet propelled rocket. The rocket's velocity is approaching light speed, therefore hovering the swinging ...
Apsteronaldo's user avatar
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2 answers
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Is the intensity of a light wave related to frequency of the wave?

My problem is: How can I resolve these following ideas? Energy of photons in an EM wave is proportional to the frequency of the wave Intensity of an EM wave is proportional to the energy that is ...
syndromeofme's user avatar
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Roughness reflectance relationship

i am confused about a result in paper related to reflectivity from etched hole in silicon. The reflectance oscillation varies with surface roughness but i am not getting similar oscillation while ...
aawer's user avatar
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10 votes
2 answers
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Can we understand from basic QED, why is the photon electrically neutral?

The QED Lagrangian $$\mathcal{L} =-\frac{1}{4}F_{\alpha\beta}F^{\alpha\beta}+\bar\Psi(i\gamma^\alpha D_\alpha-m)\Psi,$$ where $D_\alpha=\partial_\alpha-ieA_\alpha$, is invariant under $$\Psi\to \Psi'(...
Solidification's user avatar
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1 answer
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Light wave/photon doppler effect

So I understand the explanation/derivation of doppler effect from the perspective of wave crests emission being stretched out as the source moves. But how does this work from the photon point of view? ...
ABC's user avatar
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2 votes
1 answer
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In inelastic scattering between photons and electrons, how does light only partially transfer energy?

In the case of elastic scattering or absorption between photons and electrons, the incident light is either fully reflected or fully absorbed and hence it either retains its wavelength or ceases to ...
Razz's user avatar
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Photon flux for coherent waves

Coherent waves posses a well defined phase and thus not a well defined photon count. On the other hand (according to Hecht in his book "Optics" eq 3.49) we can define a mean photon flux for ...
user509065's user avatar
1 vote
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101 views

Photon loss errors versus photon subtraction errors

Cat codes, $|0_L\rangle\approx|\alpha\rangle + |-\alpha\rangle $ and $|1_L\rangle\approx|i\alpha\rangle + |-i\alpha\rangle$, are said correct single-photon loss errors in the literature. Similarly, ...
Saurabh Shringarpure's user avatar
2 votes
2 answers
116 views

Can radiation from an accelerated free charge particle be quantised in-terms of photons?

Over last few days I have been overwhelmed by the following riddle or maybe a simple misunderstanding. A free particles does not possess quantised energy levels and the entire energy of it can be ...
Subhadip Saha's user avatar
3 votes
2 answers
167 views

In the double slit experiment, when emitting one photon at a time, why don't all of them travel the same path?

If we fire one photon at a time, why don't all of the photons hit the barrier exactly in between the two slits? How come each photon goes in different directions? (some go through top slit, some go ...
Fuad's user avatar
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2 answers
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Are multimode states a product state of single mode states?

Books such as 'Quantum Theory of Light by Rodney Loudon (page 140)' and 'Quantum Optics for Beginners by Ficek and Rizda (page 43)' claim that the multimode state is nothing but a tensor product of ...
Pratham Hullamballi's user avatar
1 vote
1 answer
183 views

Can photons form a black hole?

Can photons form black holes the same way as other matter? If there happens to be enough of them concentrated in an area of space so that enough energy exists within a radius to form an event horizon, ...
user23952's user avatar
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1 vote
0 answers
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Do Energy get absorbed by electrons if is less than the Work Function? [duplicate]

It still haunts me that during photoelectric effect, incase the energy ($hv$) of the photons is less than the work function, (ofcourse it doesn't get emitted, heard that a hundered times even after ...
Elizabeth Huffman's user avatar
2 votes
2 answers
194 views

How does partially constructive and partial destructive interference work in interferometers?

From what I have gathered, complete constructive or destructive interference results in all light or no light traveling a given path of an interferometer (correct me if this is incorrect). However, ...
OneStrangeQuark's user avatar
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1 answer
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Pair production and observation of high energy photons

Pair production occurs when a photon with sufficient energy produces a particle and an anti particle. For this to happen with an electron-positron pair the minimum required energy of the photon has to ...
Exterminator2004's user avatar
3 votes
1 answer
200 views

Confusion on Energies of absorbed and emitted photons

My physics teacher shouted this atleast 3 times yesterday, 'a photon can be absorbed only when it's energy is EXACTLY equal to the energy difference between the energy states' So my understanding is, ...
Elizabeth Huffman's user avatar
3 votes
2 answers
194 views

Why doesn't a photon state have to be infinite in length?

In all discussions I've seen so far (old quantum theory, semiclassical QM, QFT), when we talk about photon states, we seem to say they have a definite momentum. At the same time, we also say a photon ...
Maximal Ideal's user avatar
-3 votes
1 answer
79 views

Photons that escape the universe [closed]

According to my current understanding of special relativity, photons do not experience the passage of time. It is as though the universe is completely 'paused' for them. I know that objects with mass ...
SPANDAN DASH's user avatar
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0 answers
43 views

Far-field analytical solution

I want to compare FDTD far-field solution for reflective diffraction with analytical solution. It seems more complicated than transmission diffraction. Please suggest resources or codes for reference.
4 votes
2 answers
498 views

Compton scattering with free electron

When the photon is incident on free electron, we say that compton happens. Though, we require that photon is x-ray or gamma ray. I wonder why at least x-ray is required. I have my own observation and ...
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