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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Photons are massless then how do they exist? [duplicate]
If something exists, then it surely has some mass. If photons are massless then they simply should not exist. But they not only exist but have momentum(p) also despite the fact that p=mv and if m=0 ...
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How many electrons with energy of 1MeV pass through plexiglass that's 2cm wide?
I am an undergraduate student and have a question. I was doing a Compton experiment and was using plexiglass to minimize electrons from radioactive source.
I was wondering how many electrons can pass ...
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How do the entangled photons from an SPDC source behave?
As I understand SPDC sources emit entangled photons, but always in the same polarisation. If this source always outputs this certain polarisation are the photons then still in superposition of each ...
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What determines how wide are the absorption spectrum lines of atoms?
So let's assume we have atoms in their ground state and we measure what kind of wavelengths those atoms can absorb. These should occur at photon energies that correspond the the energy gaps between ...
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Can photons be seen in a superconductor?
In the video Electromagnetism as a Gauge Theory, Richard Behiel states that electromagnetism is a result of adding local phase symmetry to the Dirac equation. He also says (at 3h9m) that this phase ...
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Effective Lagrangian for neutral pion to photons [duplicate]
How would I write the effective Lagrangian in the lowest order perturbation theory for the (standard model tree-level prohibited) process $$\pi^0\rightarrow 2\gamma?$$ My first guess would be ...
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Pole structure of the photon polarisation tensor
When it comes to the photon polarisation tensor in the book of Peskin & Schroeder on page 246, it is said:
Notice that as long as $\Pi(q^2)$ is regular a $q^2=0$, the exact propagator always has ...
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Intuition for Planck-Einstein relation for other particles than photons
The Planck-Einstein relation E=hf for photon can be extended for any other particle. Describing total energy this way feels relatively intuitive for photon, at least partly because we have easily ...
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How does Compton Scattering prove particle nature of electromagnetic radiation? [duplicate]
In Compton effect, just a photon playing pool, hitting an electron and bouncing off.
But in Arthur Compton article,
this effect demonstrated the particle nature of electromagnetic radiation.
How does ...
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How does a mirror lose mass during photon reflection?
When a photon is reflected by a mirror, it transfers momentum to the mirror, causing the mirror to gain kinetic energy. However, the photon's energy does not change. This seems to imply that the ...
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What is the shortest/longest wavelength of a photon? [duplicate]
What are the largest/smallest possible wavelengths of photons? I am interested in what limits apply to photon creation.
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Stacking transparent solar panels would increase the efficiency of the system?
From what I could understand, there are multi-junction solar panels that are transparent in certain wavelengths and opaque in others, but I'm not referring to them.
I'm referring to the idea of ...
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Can a microwave antenna detect single microwave photons?
In a lecture about satellite sounding our professor explained how microwave radiance is measured typically on satellites: There is an antenna behind a parabolic mirror and the received signal is ...
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Are we sure photons are particles, given that a 1 Hz photon is bigger than our planet? [duplicate]
A photon of 1 Hz has a wavelength of 300000 km, making it bigger than our planet. Are we sure photons are particles ???
lambda = c/f = 300000/1 = 300000 km
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Phase cancellation in beams of light- edited
I am reading Anil Ananthaswamy's book on double-slit interference and I realized that there's something which I thought I understood about this, but actually do not- as follows:
Photons propagate ...
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Single photons in deep infrared
Experiments with single photons in the optical wavelength are by now classic (e.g. Alain Aspect 1980's). The sources for these photons are single atoms or molecules.
Q: were single photons observed ...
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Experiments carried out to determine the energy of photons of different wavelengths
I imagine it would be very difficult to experimentally determine the energy per photon of monochromatic EM radiation. Since every material reflects/absorbs differently at different wavelengths, I can ...
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Why does from blue to red light (after crossing a prism) the heating effect on interaction material increase?
I was reading this paper for Near Infrared discovery The history of near infrared spectroscopic
analysis:
In his experiment Herschel projected a rainbow on to a bench by the aid of a prism then he ...
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Replacing the first beam splitter with polarizing beam splitter in the Mach-Zehnder Interferometer
For the single-photon interference in a Mach Zehnder Interferometer, if we replace the first beam splitter with a polarizing beam splitter, what would happen? Would the single photon still interfere ...
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Is Rabi cycle a coupling of laser-atom as two resonators? Are photons travelling in both directions there?
Trying to understand Rabi cycle, I thought it resembles coupled pendulums/resonators like in the animation - wanted to ask if it is appropriate analog?
laser is large pumped directional resonator,
...
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When a star slows down due to the Poynting-Robertson effect, where does its rotational energy go?
Today I found out the Sun's rotation is slowing down. I can see that the slight angle (on average) of the photons leaving a star, combined with the incoming nature of the surface as seen from that ...
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Dipole transition in solid state systems and incident angle of photons
In solid state systems, there are energy transitions (absorption and emission of photons) that are photon polarization selective. I believe any sort of photon absorption based transitions comes down ...
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Can UV Light Also Act to Heat a Metal Like IR?
I am familiar with the photoelectric effect. For example, aluminum has a work function of between 4.1 to 4.3 eV. So if ~295 nm UV light is shined on aluminum, some conduction electrons will absorb ...
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Polarization, quantum number associated with
Why does a photon with left circular polarization has a +1 angular momentum $lz$, while a photon with right circular polarization has a -1 angular momentum, instead of left circular polarization ...
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Why can't we see individual air molecules?
I always wonder, as we all know, we see the sky as blue because the air molecules scatter MOST of the light in blue range, but why can't we see individual air molecules in the atmosphere (or just ...
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Squeezing degredation via photon loss
Consider a partially reflecting beamsplitter with two input modes $\hat{a}_{in}$ and $\hat{b}_{in}$. It has a transmission coefficient of $\eta$. If the photon in mode $\hat{b}_{in}$ is in the vacuum ...
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How many photons does an X-ray tube emit?
I want to estimate the number of photons emitted by an X-ray tube under the following assumptions:
The tube is a tungsten tube at 60 kV, 1 mA, no inherent filtration.
The X-ray tube converts roughly ...
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What is photon direction of backward ASE (amplified spontaneous emission)?
While "laser causes excitation" is natural, CPT symmetry requires also "laser causes deexcitation" scenario, both used e.g. in STED microscopes through diode lasers.
In common ...
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Confusion between wave frequency and photon frequency
Suppose I have some electrons in a wire which are moving up and down, in sync, where the position is given by $x = \sin(2\pi ft)$. At times $n/f$, there is no acceleration and therefore not emitting ...
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Why do photons obey Bose-Einstein statistics?
In a typical derivation of Bose-Einstein distribution using Lagrange multipliers, the total number of particles is assumed to be fixed. But for photons, the total number is not fixed, say in blackbody ...
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Can noninteracting Bose-Einstein condensate reach infinite density?
If particles are noninteracting, does it mean that the density can be infinite in the ground mode of the Bose-Einstein condensate?
For example, here they are investigating the photon condensate ...
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Atomic off-resonance absorption in a full quantum theory
When studying atomic absorption in time-dependent theory, we learn (see, for example, Griffiths, 1Ed, pg. 307), that the probability of absorption is given by,
$P_{a\rightarrow b}(t) \propto \frac{\...
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Gravitation Pull Photon observer dependent
does the gravitational Pull a photon exerts depend on the observer? Since a photons energy changes due to length contraction depending on the observers speed, shouldn't it exert a different ...
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Can you redirect an electromagnetic interaction with a mirror?
Sorry if this question is a bit naive, but, if photons mediate electromagnetic interactions, can you deflect those interactions with a set of mirrors or gravitational objects? And would this result in ...
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Connection Between Quantum Phase Shift Gate and Phase Shift in Oscillating Electric Field
I'm trying to model a Mach-Zehnder interferometer. The linear algebraic description of the phase shift matrix $P = \begin{pmatrix} 1 & 0 \\ 0 & e^{i\phi}\end{pmatrix}$ makes sense to me to ...
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Do maxwells equations describe the probability (conjugate squared wavefunction) distribution of light? [duplicate]
Before quantum theory was developed, Maxwell's equations were deemed to accurately model electromagnetism and light.
The wave nature of light had been observed, as in the double slit experiment, ...
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Energy of light as EM wave and photon
In electrodynamics, light as a wave has an intensity $I = \frac{1}{2} c \epsilon E^2,$ where $E$ is the electric field amplitude.
Meanwhile in quantum mechanics, we study $I = \frac{dn}{dt} \frac{hc}{\...
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The cosmic speed limit
We already know by the postulates of Relativity, that the maximum theoretical possible velocity of a body is c or 299,792,458 m/s to be exact.
Also, if we think that the relative velocity would be ...
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Are there 12 interaction mechanisms between photons and matter?
According to this textbook, Physics for Clinical Oncology, p.24:
There are thought to be up to twelve ways in which photons interact with matter of which only three are of relevance to the radiation ...
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When an electron jumps from higher to lower orbit, how does it not violate the law of conservation of mass?
I am just a higher secondary school student who was recently studying Bohr's model of the atom when this question popped into my mind. I know that when the electron jumps to lower orbits it releases ...
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An object's colour and its relation to light
I know that an object (say, a block of red colour) appears red because white light from the light bulb or sun shines on it, and the block absorbs all the other wavelengths of light except that ...
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Photonic clock and diagonal path (again) [closed]
I did went through some answers on here and reddit about this question and got some interesting insights about what could be going on but still no answer totally solved the question for me.
So, ...
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Are photons both waves and particles, or particles subject to a probability wave? [duplicate]
We know that photons exhibit wave-like behavior, as demonstrated in the double-slit experiment. As the force carriers for electromagnetic interactions, photons are also particles. Does a photon's ...
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"Negative time evidence" in the news - are they really observing causation backward in time?
There are many news about recent https://arxiv.org/abs/2409.03680 by Aephraim M. Steinberg group, e.g.:
https://www.scientificamerican.com/article/evidence-of-negative-time-found-in-quantum-physics-...
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Separate dust particles by colour by light
I have a stream of dust with coloured particles. I want to sort those particles by color. We are wondering if it is possible to let it flow by an intens light in a specific color and then extract the ...
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Can we ever know the exact polarisation of a given photon?
When we pass photons with randomly orientated polarisations through a vertical polarising filter, half the photons that pass through are said to be vertically polarised, but in reality they have a ...
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What would happen if all the matter and antimatter in the universe annihilated? [closed]
Assuming matter and antimatter in the universe are in equal amount, if they would annihilate,would the universe be left filled only with photons, resembling the state of the early universe? ...
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Qualitative confusion about whispering gallery modes
I've been trying to wrap my brain around aspects of whispering gallery modes for a while now (in a qualitative sense, I'm not trying to solve for anything yet).
So, a whispering gallery mode is a ...
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A simple fact I can not explain to myself using Copenhagen interpretation?
Let’s describe briefly the Michelson-Morley experiment in terms of single photons. A photon is launched by a laser from point A and meets the BS beam-splitter 50/50 in point B. Then it has two equal ...
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Does the time until $k$th photon arrival follow a Gamma distribution?
Assuming that photons in every macroscopic light source have Poisson statistics, it should follow that the waiting time until the $k$th photon has been emitted has a Gamma distribution, right?
From (...
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