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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How to align a Mach-Zehnder at 810 nm?

I have a task to arrange MZI using very weak source with photons coming one at a time. On top the wavelength is 810 nm. How to 'see' the interference pattern to 100% in one channel and 0% in other. I ...
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Pushing solid objects by photon exchange

As I understood it, the reason I cannot stick my hand through a metal block is due to the repelling force between electrons in my hand and in the block. QED depicts two electrons repelling with a ...
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Does a dimensional analysis of Einstein’s equation describe a rapidly expanding area? [closed]

The speed of light, C, is measured in meters per second. C squared, therefore is measured in meters squared per second squared, a rapidly expanding area. So my interpretation of is that as a photon is ...
user2976503's user avatar
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Can there be cases where the photons crossing the voids have a total net blueshift as they get out of them?

I was reading this paper (https://academic.oup.com/mnras/article/288/2/387/960778) where the authors analysed how CMB radiation is affected by evolving voids in an expanding spacetime (particularly ...
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What is the Lagrangian for the interaction of graviphoton with matter?

There are some models that postulate the existence of graviphoton. What is the Lagrangian for the interaction of graviphoton with matter?
physics_2015's user avatar
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Why increasing the voltage of the anode with respect to the cathode has no effect on the photocurrent?

As light strikes the emitting electrode, electrons are ejected. But not all of the ejected electrons are collected at collecting electrode since they don't all get ejected in the same direction. ...
Jack's user avatar
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Single Photon Detection in a Moving Train of Detectors Setup

I’ve been pondering a thought experiment related to quantum mechanics and photon detection, and I’m curious about the theoretical outcome and whether any similar experiments have been conducted. ...
Alex Jonathan Henderson's user avatar
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Recently a paper published showed light could be slowed down 10,000 times. Could this be used to accelerate spacecraft as energy cannot be lost?

Light has no mass. So simply assuming F = M x A Will generate a zero answer. However, in slowing down light there is a reduction in energy. Energy cannot be lost only transformed. People have ...
Steve Count's user avatar
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Emission of a single photon

When a single photon is emitted as a result of an electronic transition, it will have a defined energy and wavelength. However, its amplitude is not constant over infinite space and time; instead, it ...
Tobi's user avatar
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How to distinguish Coulomb and radiative parts of the electromagnetic field?

In classical electromagnetism, the EM field can be described by a 4-potential $A^\mu$. This potential describes two different phenomena. Static fields: A static charge $q$ at fixed position $r_0$ ...
P. C. Spaniel's user avatar
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Is each INDIVIDUAL photon a PHYSICAL wave? [closed]

Sigh. So I've scoured the internet for many many hours, on many many occasions... aaand, yeah. Is light: just ONE photon which acts like a physical wave as those seen in classical mechanics (if so, ...
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Accordingly to the classical theory, if the electrons' energies depend on the intensity, then on what does the electrons' number depend?

In the photoelectric effect, accordingly to the classical theory, if the electrons' energies depend on the intensity of the incident light, then on what does the electrons' number depend? I mean, how ...
Jack's user avatar
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Is the interference stable?

In a Mach Zehnder interferometer if we use one at a time photons and tune it so the first several to arrive in channel D1 after BS2 will all next arrive also in D1? Are there reasons that some will ...
Mercury's user avatar
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Photon pair generation

Where one can buy a crystal for photon pair generation? Can it work with a LED to be registered with a CCD or LED is low and a laser is needed? Thanks very much for who can help. I found a company ...
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Is quantization chosen as a model due to us primarily observing light generated by atoms?

The two main ideas that led to quantization are Planck's solution to black body radiation and Einstein's solution to the photoelectric effect. In both cases, we are dealing with absorption and ...
Blacklight MG's user avatar
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Why do lattice structures absorb more photon frequencies than single atoms?

I'm trying to understand why the liquid-like structure of glass is necessary for it to be transparent.
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What happens to a single photon in case photoexcitation doesn't occur upon "hitting" an electron of a single atom

I'm having trouble finding sufficient answers that don't boil down to discussing materials. Some people say that if a photon does not excite an electron it doesn't interact with it at all and just ...
bansheenocturno's user avatar
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Can a CCD work in time integration regime?

Can one use a CCD in same way as photosensitive paper? When one has very low intensity like in single photons double slit experiment to see the interference pattern one puts a photosensitive paper at ...
Mercury's user avatar
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What is the difference between photons and electromagnetic waves?

Electromagnetic waves are generated by accelerating electric charges. Photons on the other hand, tend to describe something different, specifically the particle nature of electromagnetic waves as ...
Blacklight MG's user avatar
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Photon momentum in Snell's law of refraction

In the drivation of Snell's law for light as EM waves, we have the wave vector components parallel to the interface $k1\parallel$ = $k2\parallel$ as shown in the picture. From $k_{1x} = k_{2x}$, we ...
Leon Chang's user avatar
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Converting time-bin diagram to second order correlation function

Considering characterization of single photon sources a second order correlation function $g(𝜏)$ is used to determine the purity of a single photon source, specifically its value at $g(0)$. Now ...
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If matter cannot be created or destroyed, how were scientists able to "create" matter out of light? [duplicate]

It has been proven that scientists are able to "create" (using quotations because I do not understand if it is creating or not) matter from light in a particle collidor. How is this possible ...
Ryan Jadhav's user avatar
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Energy of "free" gluon

Does exist, if it make sense, a formula to describe the energy of a gluon, since its creation to its absorption, like the formula of Planck for the photon $\hbar\nu$?
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SPDC entangled photons and orbital angular momentum?

I know that spontaneous parametric down conversion (SPDC) produces entangled photons in the orbital angular momentum (OAM), i.e., for a pump beam with zero OAM, $ |\psi \rangle = | 0 0 \rangle + | 1 -...
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Can there be an electron without photons?

Can the electron field be excited while the photon field is not? I'm guessing the answer is no, because electrons are supposed to interact with their own electric field. I don't know about ...
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Physical interpretation of photon propagator

Physically, propagator represents the probability amplitude of a particle to travel from one point to another. But the photon propagator $$D_{\mu\nu}(x,y) = \langle 0 | \mathcal{T}[A_\mu(x) A_\nu(y)] ...
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Can we consider that the photons that were not and will never be detected live in a zero-dimensional space?

According to Einstein’s theory of relativity, any particle traveling at the speed of light experiences no passage of time. It follows that if a photon travels through space then within any two points ...
David's user avatar
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The Role of Harmonic Frequencies in Natural Phenomena

I am deeply fascinated by the apparent intrinsic relationship between harmonic frequencies and the natural world. This relationship is evident not only in the mathematics that simplify our description ...
CuriousMind's user avatar
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The idea behind Sagnac loop for entangled pair generation

I have a question which I cannot intuitively understand. In many articles I saw a Sagnac loop being used to generate polarization entangled pairs of photons. The principle is rather simple - you split ...
Gustas's user avatar
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How many photons exist in another dimension spaces?

As I understand, there are 2 types of photons in our (3+1) space with photon helicity $\pm 1$. How many photons exist in another spaces like (2 + 1) or (1 + 1)? Can we apply the same for gravitons?
Aslan Monahov's user avatar
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Difference in light falling into a room depending on the positioning of the sun

How does the lighting falling into a room differ in color temperature, shadow productions, directionality and other aspects, in relation to the positioning of the sun and the room? For example, if the ...
vannira's user avatar
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Photons and gravitational wave

Both photons and gravitational disturbances travel at $c$. Given that a photon does cause a tiny stress in spacetime due to its energy, and the propagation of this stress is at the same velocity as ...
Rich's user avatar
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2 answers
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Is spatial distance objective?

While reading some papers on Einstein's theory of relativity, seeing how the flow of time is not the same for everyone, a doubt occurred to me: Let us imagine a photon moving in a well-defined space ...
Stream Sphere's user avatar
1 vote
1 answer
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An optical detector that guarantees single-photons detection

Let's consider a real source emitting a sequence of single-photons (like for example a N-V colour centre pumped with a pulsed laser with highly accurate frequency of the pulses). I want to ...
Ang's user avatar
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2 answers
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Which factors determines whether a photon is absorbed? [duplicate]

After some research, I figured out that all EM waves/photons are absorbed by atoms by exciting an electron from an orbital to an other. However, atoms emit only certain EM waves with specific ...
shar's user avatar
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1 answer
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Why does there need to be a particle representation of light?

Why does there need to be a particle representation of light? Doesn't light as a wave explained the observations of the photoelectric perfectly? When the frequency of light is increased, the speed of ...
ThreadBucks's user avatar
2 votes
2 answers
106 views

Parity of Photons

In nuclear physics, while studying gamma decay (Nuclear physics, Roy and Nigam, 1st ed, pp 450) I have read that the parity of photons depends on the type of multipole radiation they represent. Means ...
Sagar K. Biswal's user avatar
5 votes
3 answers
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Connection between photons and EM waves

We learn about electric and magnetic fields and how they conform EM waves. Then we discover the photon and how there was a duality between this two ideas, sometimes radiation behaved like a wave and ...
Luis catuxo's user avatar
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What is momentum exactly? [duplicate]

What is momentum exactly? I am confused that, is momentum a property of particle or something different. Whenever i look for it's definition it is product of mass and velocity of a particle. At ...
Vidushi Aggarwal's user avatar
1 vote
4 answers
174 views

Since light has inertia and experiences gravity, what does it mean for photons to be massless?

I've been trying for a long time to figure out what the heck mass even IS. In introductory physics and chemistry, students are told that massive objects are those that are made of matter and take up ...
Mikayla Eckel Cifrese's user avatar
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2 answers
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Electromagnetic field affect on hydrogen atom energy levels

If hydrogen atom is in the ground energy state it must be hitted by photon with energy higher than electron proton energy binding which is 13,6 eV according quantum mechanics. Proton have positive ...
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(L&L vol. 4, sec. 59) Matrix Elements of the Electromagnetic Interaction Operator

In Sec. 59 ('The Scattering Tensor') of the fourth Landau and Lifshitz gives the matrix elements of the electromagnetic interaction operator $\hat{V}=-\hat{\boldsymbol{d}} \cdot \hat{\boldsymbol{E}}$ ...
wannabephysicist's user avatar
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2 answers
80 views

What will happen if a photon collide to itself [closed]

What will happen if a photon rotating in LHC so fast it catches and bumps to itself?.
jmazaredo's user avatar
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3 votes
1 answer
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Explicit examples of sub-poissonian photon number distributions

I am aware of the Poisson and Bose-Einstein distributions as explicit distributions for Poissonian and super-Poissonian photon number distributions. Specifically, the photon number distribution for ...
Aaron Hendrickson's user avatar
1 vote
3 answers
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How does light not have mass? [duplicate]

How is it possible for light to have zero mass because it was my understanding that in order for "stuff" to exist it has to have some form of mass? And if it does not have mass then can it ...
chocolate king's user avatar
8 votes
2 answers
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How does a photon "cheat" its way past a neutron?

I learnt here Is a neutron deflected sideways by a laser beam? that a photon beam has no influence on the motion of a free neutron in the first and second approximation. Now I'm interested in what ...
HolgerFiedler's user avatar
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Are intensity vs wavelength graphs really continuous? [duplicate]

For hot bodies we generally draw graph between intensity and wavelength similar to one in picture. My question is this graph really continous? If it is continuous, does it not mean there are infinte ...
bdogwjumiz's user avatar
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1 answer
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Measurement in Double Slit Experiment

In physics, the observer effect is the disturbance of an observed system by the act of observation. A notable example of the observer effect occurs in quantum mechanics, as demonstrated by the double-...
Ok-Virus2237's user avatar
1 vote
1 answer
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Splitting single photons

Regarding splitting a photon, I found reference to the splitting of a high energy photon into two lower energy, entangled photons, this within the thread 'Application of splitting a photon into two'. ...
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Tunnel ionisation and how to interpret changes in potential curve

I have been doing some literature review on species ionisation to understand a particular mechanism that occurs when a high-intensity femtosecond laser interacts with molecular nitrogen to produce ...
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