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 ...

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How SPAD work over Break Down voltage?

SPAD (Single Photon Avalanche Detector) works beyond Breakdown Voltage which is mentioned as Geiger Mode. But how this actually working. When bias voltage aceede breakdown voltage, generally high ...
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1answer
57 views

Is it possible to create a pair of polarized, polarization-entangled photons?

Is there a light source which emits (mostly) polarization-entangled pairs of photons that have a known polarization angle, e.g. a certain angle in relation to the orientation of the source? Applying ...
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44 views

Aim of photon gun in a double-slit experiment

Hope someone can enlighten me on the following questions: In a double-slit experiment with photon, how is the photon gun aimed? If the photon gun is set up to aim at the barrier space between the ...
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19 views

Hologram: How does the interference path of reflected and reference waves change as we move?

I've seen this and this and read this. Either I got dumber in times or these are not sufficient to understand how actually hologram works. I understand how reference light and reflected light ...
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2answers
69 views

How can we see stars and galaxies if photons are travelling straight?

This may seem a dumb question but I can't visualize this in my mind. If photons are travelling straight then from our eyes or a telescope we should only see part of the star, for example because our ...
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2answers
60 views

Does the size of a photon change depending on the energy level/wavelength of the light? [duplicate]

Basically the title. And if so, is there a proportional relationship?
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3answers
125 views

What is the amplitude of a light wave?

Referring to this question How can I measure the amplitude of a light wave? I'm curious about what is a amplitude of a light wave. Especially for light from a thermic source.
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2answers
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Why are photoelectrons emitted in the direction of incident photons?

In the experiments for photoelectric emission, the light is incident on one face of the emitting plate, for example the anode, when determining the stopping potential. The electrons are emitted by ...
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Is there a connection between the frequency of a photon and the oscillation frequency of the atom which absorbs it?

If a photon has energy $E$, we know it has angular frequency $\frac{E}{\hbar}$. If an atom has an energy gap $E$ between its ground and first excited state, we know that if the atom is in a ...
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3answers
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Concequences of the speed of light beeing absolute? [duplicate]

If photons have a speed limit (speed of light), what happens when you shoot photons through a flashlight but you yourself already have some speed? Do the photons from the flashlight only travel at [...
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5answers
188 views

Coherence length of a single photon

If I pass individual photons through a M-Z interferometer with equal arms I will observe interference (eg only one detector will respond). As I increase the path length of one arm I will observe the ...
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1answer
47 views

How frequently do accelerating electrons emit photons?

In the quantum 2-slit experiment with light, we know that as the source intensity is turned down, individual photons arrive at the detector. I would like to know if there is a formula which tells us ...
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156 views

What is entanglement really about? [closed]

I am a beginner in this field, I am trying to understand the basics of Quantum Mechanics, I want straightforward answers to few questions on entangled photon/electron: 1- What entangled photons ...
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2answers
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Does 'real' photon electromagnetically interact with matter?

Consider the standard description of Compton scattering - radiation is constituted of stream of photons (these are supposed to 'real' as contrasted to 'virutal' photons of the QED). One of these ...
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60 views

Could a photon also be a fermion? [duplicate]

Some phycisits have found photons that has a spin of 1,5. Now fermions has always a half spin and bosons like photons always with a whole spin. But if those photons really exists are they than ...
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1answer
53 views

Gaining some intuition: Photon bunching

This is a very easy question: I'm in need of some intuition on the fact that, e.g. thermal sources, produce bunched photons. It is very easy to "undertand", without any quantum mechanics, why single ...
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0answers
25 views

Does photon experience time? [duplicate]

According to the special theory of relativity, for all observers the speed of light is c. Any observer travelling at the speed of light c does not experience time. Hence even protons shouldn't ...
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1answer
109 views

According to Einstein & Brian Greene, does the photon remain stationary in the fourth dimension? [duplicate]

According to Einstein and Brian Greene, does it logically follow that the photon remains stationary in the fourth dimension? In An Elegant Universe, Brian Greene writes: “Einstein found that ...
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3answers
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Why can't electrons absorb any energy (i.e. absorb some energy of the photons necessary and emit the residual)?

Recently I had a question in mind about the absorption of photons. Why is it that only specific energy levels can be absorbed by electrons? I mean, I get the idea that electrons in an atom have only ...
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0answers
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Can a photon be emitted if it is also not received?

In GR, the space for a photon is zero, so the destination is the same as the point of departure. In QM, a photon is an interaction between 2 charged particles. So basically, a photon cannot exist if ...
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1answer
91 views

Can light be a spinor?

A recent discovery suggests that photons can have half-integer spins. This seems to contradict the well understood notion that photons are vector (1-form) fields What does this mean for the ...
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1k views

Photons with half integer angular momentum - what's happening?

I have just read this article - what is happening? Analysing these beams within the theory of quantum mechanics they predicted that the angular momentum of the photon would be half-integer, and ...
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2answers
82 views

Does a source of photon emission “sense” if the photon is absorbed? [closed]

Can the absorption of a photon be 'felt' by the source that emitted it? At least, if we assume that it emits a steady stream of photons? Is there a back reaction of some kind on the source?
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Why is it that light bends towards gravity when it has no mass at all? [duplicate]

Why is it that light bends towards gravity when it has no mass at all? Is it because of how gravity behaves as mentioned in general relativity? As far as I know, light cannot escape from black holes, ...
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1answer
39 views

Perfectly elastic and inelastic collision of photon

I`m having some trouble understanding (and finding any relevant information) about the elastic and inelastic collision between a photon and a mirror in non-quantum machanical terms. When a photon hits ...
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4answers
90 views

If photons travel at the speed of light how can they ever be destroyed? [duplicate]

If photons travel at the speed of light than due to relativity they must experience no time frame in which to be destroyed in the first place so they must be immortal which is silly. So, clearly I am ...
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2answers
63 views

How can photon have wave properties if they travel at the speed of light? [duplicate]

I am not a physicist so please excuse me if this is a dumb question. As far as I understand Relativity, as observer (in this case a photon) travels at the speed of light, time stops. So how can the ...
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4answers
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Does a box containing photons have more inertia than an empty box?

A box containing photons gravitates more strongly than an empty box, and thus the equivalence principle dictates that a box containing photons has more inertia than an empty box. The inescapable ...
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Photon in the box electric field strength

If we put a photon in a box and suppose the resonant frequency is $f$. If we know the volume $V$, How do we approximate the electric fields at the center of the box?
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1answer
70 views

Concerning The Oil Drop Experiment: How does ionizing radiation create the electron(s) that the droplets of oil collect?

Concerning the Oil Drop Experiment: I read, “Ionizing radiation is used to create the electron that the droplets of oil collect. When the air in the apparatus is bombarded by this ionizing radiation ...
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23 views

Interesting question regarding stimulated emission

why is outgoing photon emitted during stimulated emission in phase with the incoming photon? I can't see why this is so because the two photons may be out of phase yet conserving momentum and energy.
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142 views

If photons end up having a tiny mass, say $10^{-54}~\rm kg$, what would be the universal speed of massless particles?

First, I'm no expert so sorry if I get anything confused but I tried to research as much as could before asking this. So while it is pretty much accepted that photons are massless (Despite this ...
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65 views

Photons when passing through matter

I am wondering whether there is a simple—or complicated—way to explain from a purely quantum mechanics (or QFT) viewpoint what happens to the photons when they go through some material whose index of ...
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Rainbow Black Hole [closed]

In the photon sphere of a black hole the photons are being trapped in orbit, pulled in and trajectories changed. From a safe distance should we see color from the entire spectrum if light in the ...
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34 views

Electromagnetic Field caused by accelerating and oscillating charge particles?

Will accelerating and oscillating charges will cause EM waves of different shapes ? As EM waves are always shown as sinusoidal Electric and Magnetic Fields perpendicular to each other. Does it mean ...
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1answer
24 views

How can excite a semiconductor to make a photon just by heat in room temperature?

I want to know if a semiconductor in room temperature can excite by heat, producing photon, without any other source of energy?
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4answers
2k views

Same photon or different photon?

Consider a typical optical focusing system: A small light source, then a collimating lens, then a focussing lens, and then a detector (e.g. CCD). Assume that source intensity is so low that only one ...
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Is the helicity of photon Lorentz invariant? [closed]

If the helicity of a photon is $+1$ in an inertial frame, then is the helicity of this photon $+1$ in another inertial frame? The helicity operator is $$ h=\mathbf{S}\cdot\hat{\mathbf{p}} $$ with $$ ...
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Electromagnetic waves and photons? [duplicate]

Electromagnetic waves are photons or photons cause electromagnetic waves ? Its said that when charges are accelerated we get electric and magnetic field that carries energy but then they say that this ...
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4answers
304 views

How do electromagnetic waves carry energy?

Its said that electromagnetic waves carry energy. Is this because these waves are made up of electric and magnetic fields which can cause changes to the stuff that falls with in their range? Is that ...
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2answers
170 views

Nature of light in Special Relativity

What is the nature of light in the context of Special Relativity? Is it a photon, or an electromagnetic wave, or something else? I have doubts, because a photon seems to me a quantum mechanical ...
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How could you slow down or change direction with photonic propulsion?

So you have a laser shooting at a sort of solar sail to transfer momentum in the forward direction but could you have an onboard laser and turn the laser around to hit another sail? How could you turn ...
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Calculating saturation current and energy associated with a band of wavelengths

Consider white light whose wavelength spread is from 400nm to 700nm. Its energy is uniformly distributed in this spectrum. The light is incident on metal A of work function 1.55eV. Saturation ...
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3answers
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Does an electromagnetic wave necessarily contain many photons? [duplicate]

I've often come across people saying from a quantum physics standpoint that an electromagnetic wave necessarily contains many photons. But doesn't the double-slit experiment conducted one photon at-a-...
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1answer
46 views

What determines the color of photon that is emitted from an exited atom?

I understand the principle of how light is emitted from an atom. What I don't know is why neon atom is red and copper is green when exited? Is is the distance between the electron to protons or the ...
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24 views

Pair production in different reference frames

I understand that energy of photons is defined by their wavelength/frequency. This frequency (and so energy) will be different for different observers: observer moving towards the photon will see ...
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57 views

Does a photon follow a straight trajectory in a thin transparent film? [closed]

Emulsion films (developed by F.Powell) /by example/ show that elementary particles follow a straight trajectory staying in a film. The reason was clarified by Francis Mott in his famous 1929 paper ...
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1answer
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Is linear polarization of entangle photons in 2-particle decay always correlated?

In Aspect's paper "Bell's Theorem: The naive..." and in an 2002 AJP article by Dehlinger and Mitchell "Entangled photon apparatus..." the photons are described to be in the $|xx\rangle+|yy\rangle$ ...
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62 views

Coulomb law and photons

When we consider process like $e^- e^- \to e^- e^-$ in QED, we see that from exchanges of one photon (tree-level diagrams) one can obtain Coulomb's law, while loop-diagrams give quantum corrections ...
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61 views

Why do some elements burn different colors? [duplicate]

I have a torch lighter and it makes a green color when the flame passes over the metal in the center. What on the molecular level would a flame change color although there is no difference in ...