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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Quantum coherent properties of the sunlight

My question is inspired by this one: How to identify if a photon comes from the sun? However I would like to formulate it a bit more seriously. Although in theory the photons with the same quantum ...
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How to identify if a photon comes from the sun?

Is there any way to know whether a group of particles is generated from the sun rather from an artificial source?
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Boltzmann equation for photons in cosmology

I am trying to understand the derivation of the Boltzmann equation for photons given in Modern Cosmology (2nd Edition) by Scott Dodelson and Fabian Schmidt. In Eq. (5.4) they give the zeroth-order ...
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If the Higgs field gives particles mass, and is present everywhere, then why are there massless particles?

According to this article: Imagine that all of space is uniformly filled with an invisible substance—now called the Higgs field—that exerts a drag force on particles when they accelerate through it. ...
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Partition function of a photon gas

I am trying to calculate the partition function of a photon gas. The book I'm currently following is "Thermal Physics by Garg, Bansal, and Ghosh" It does the following: The parition function ...
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Why is photon energy no function of transition time?

An electronic transition in an atom produces a photon, and the photon's energy is determined by the difference between upper and lower electronic state. For the final photon, its energy is described ...
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Can I burn a piece of wood by emitting only one photon per second on it?

Can I burn a piece of wood by emitting single photons on it? (for example by emitting only one photon per second or per milisecond etc to the wood). How much should be the rate of emitting single ...
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Photons travelling in parallel and colliding (Thought Experiment)

Suppose two photons displaced by a distance $\delta$ are travelling with momentum vectors that are parallel to each other, and further assume that no other particles exist such that the photons can ...
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Can we derive the momentum of photon from special relativity?

I don't really have strong backgrounds studying quantum physics, but I did learn special and general relativity, and I have now a question how to get the momentum of photon. For my understanding, ...
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Status of photon velocity in perturbative calculation of QED in curved spacetime

In the paper by Drummond et. al. by doing perturbative calculation of photon propagator in a curved spacetime they found that in certain directions in a given spacetime quantum correction suggests the ...
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Can black holes move at the speed of light? If so, what would its curvature look like? [closed]

This question has more to do with the curvature of moving bodies but I will first start with this. If a photon has enough energy, then it could presumably become a black hole (kugelblitz). I see no ...
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What is the difference between a photon's phase and polarization?

When talking about a photon emitted by a laser device, what is the difference between phase and polarization? Is it redundant to specify both the polarization and the wavefunction's phase? Does a ...
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Are all electromagnetic and optical phenomena ultimately caused by electronic processes?

On the Wikipedia page for Gauge Theory, it is mentioned that Quantum electrodynamics is an abelian gauge theory with the symmetry group U(1) and has one gauge field, the electromagnetic four-...
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How to deal with several photons traveling around a black-hole

Here I'm assuming the simplest kind of black holes, Schwarzschild. We already know (very well) how to deal with a test photon traveling around this black hole (for example, we can use the Hamiltonian ...
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Can a photon be detected by a “lateral” detector? [closed]

If I direct a laser pointer north and I put a photodetector eastwards (i.e. at $90^\circ$ ), and I wait for a very very long time (in a perfect vacuum if necessary), will the detector ever be ...
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EXCITON, Semiconductors

I am studying the semiconductors and how to solve the triplet and singlet excitons by using the Density functional theory (DFT) and then we will use the Kohn-Shamm and GW approximation by using Green ...
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What do you 'see' if you are stationary relative to a photon in a refractive medium?

A particle with zero rest energy/mass must always be at $c$ in all referentials, even why, if you could get to its referential it would have zero total energy, effectively not existing in that ...
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Observation of 2 Photon clocks in same reference frame [closed]

In the train station frame a photon source is pointed upwards on the track. A train with a small hole in the floor runs over this source. A half mirror will transmit 50% to the roof through a hole in ...
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Are photons always particles in QED? [duplicate]

I've been reading Feynman's "QED: The Strange Theory of Light and Matter" and was wondering how exactly does QED treat a photon. In the book, Feynman always asserts that photons are ...
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How does absorption of light occur?

When photons hit matter, the electrons in that matter get excited (if the energy of the photon is sufficient to excite the electron to a higher energy state). But we know that the electrons are ...
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Is anti-bunched light necessarily sub-Poissonian?

It is well-known that sub-Poissonian photon statistics and light anti-bunching normally occur together, since both effects may be considered as a manifestation of photon streams being 'regular enough'....
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Experimental suggestions for size and shape of single optical photon (wavepacket)?

Optical photon is an electromagnetic wave produced e.g. during deexcitation of an atom, carrying energy, momentum and angular momentum difference. So how is this electromagnetic energy distributed in ...
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Black holes bending light [duplicate]

Ok so I've been watching some videos about black holes but there is one thing I don't get: how can light be bent by black holes since photons don't have any mass?
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Does $E^2=(mc^2)^2+(pc)^2$ hold for light travelling in an optically dense medium?

The rest mass of photon $m_0=0$ and photon travels at the speed of light in vacuum. So the energy of photon in vacuum is given by $$E_{vacuum}^2=(m_0c^2)^2+(pc)^2=(pc)^2$$ $$E_{vacuum}=pc=\gamma m_0c^...
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Can an incident photon interact with/be affected by a magneto-static field?

A photon traversing through a magnetized material has it's polarization rotated. This is called the Faraday Effect and is quite heavily studied. But can an incident photon, like the one created by ...
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Photosynthesis relation to work function and photoionization

When photosynthetic organism’s use pigments such as chlorophyll, the metal ion in the center emits an electron after absorbing a specific wavelength of light, at 400-700 nm This does not make sense to ...
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1:1 Beam-splitter and the Hong-Ou-Mandel effect

We can write the state of two photons in different modes: $$\tag{1} \hat{\alpha}^{\dagger} \hat{b}^{\dagger}|0,0\rangle_{a b}=|1,1\rangle_{a b} $$ According to the Wiki page on the Hong-Ou-Mandel ...
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Work from the absorption of a perpendicular photon?

A photon hits an atom perpendicularly to its speed v and it is absorbed as is known immediately. So it can not act after the time when it is not perpendicular (e.g. the force is 0 after that). ...
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How to calculate redshift/scale factor of matter-radiation equality without current density values

I am trying to solve a cosmology problem and I am stuck. Initially, I am given the following assumptions: a spatially flat universe that contains relativistic matter only. I have had to derive the ...
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Can photons only exist in the state of motion?

Photons are known to travel at a speed of 299 792 458 m / s in vacuum. Photons can be absorbed, or absorbed and re-emitted by matter. They slow down to 225,000,000 m/s in water with a refractive idex ...
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Hubble telescope: forces and torques due to radiation pressure

The Hubble telescope spacecraft uses six rate gyroscopes for orientation sensing. It is well known that even the best inertial measuring units accumulate drift or integration errors due to bias and ...
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Compton scattering: What is the probability distribution of different scattering angles depending on applied wavelength?

Compton scattering: What is the probability distribution of different scattering angles depending on applied wavelength? As I understand the physics of waves shorter wavelengths are like tiny bullets ...
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Neutrino temperature

I was wondering if anybody knows the relation between the photon temperature $T$ and neutrino temperature $T_{\nu}$? And why this can be written as $$T_{\nu}=\left(\frac{4}{11}\right)^{1 / 3} T \...
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Variables in Photoionization and Work Function of metals

Do metals engaged in coordination bond have the same work function and/or photoionization of the pure metal? The outer electron shell still remains the same. If photoionization were to happen, what ...
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What's the force experienced by a hydrogen atom when it absorbs photons?

Suppose a hydrogen atom is a distance $d$ away from a star (approximate the star as a blackbody). The radius of the star is $R$ and the its temperature is $T$. The hydrogen atom absorbs photons from ...
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About two photon interference in nanophotonics

Within the standard model, photons are point particles, i.e., with no spatial distribution. On the other hand, classical electromagnetic modes have field distributions. Suppose there are two different ...
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Calculating the wavelength of incident photon in Compton scattering event

'In the Compton scattering event, the scattered photon has an energy of $120$ keV and the recoiling electron has an energy of $40$ keV. Find the wavelength of the incident photon.' I thought, to solve ...
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How does a photon know what to do when It interacts with the first surface of a LIGO mirror?

There are 72 alternating boundaries (optical coatings) to traverse before it can decide whether to reflect or pass through the mirror. The boundary properties are such that the the first boundary by ...
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Experimental arrangement of photo current

In my book it say that between the cathode and anode there exist number of electrons which make the space charge. When light falls on cathode photoelectrons are released but is repelled by the space ...
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Proving the equation that relates Kane's parameter $P$ to the effective mass of the electron

Derive Eq. (4.2.26) for Kane's parameter $P$. The question below is from page 173 by Physics of Photonic devices by Shun Lien Chuang. I have no idea where to start.
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Why is the Energy of the photons and the Free Energy of the electrons compatible in a solar cell?

Why are the Energy of the photons and the Free Energy of the electrons compatible in a solar cell picture (band bending, etc)? Band gap (energy) and Fermi level (free energy per electron) are shown ...
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In what directions do a photon and an electron move after they collide?

Suppose a billiard ball moves in a straight line and the center of another billiard ball is at a distance from that line of less than the radius of a billiard ball. That distance determines which ...
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Why are the wavefunctions of the excited states so symmetric?

The excitation from a lower level to an excited state happens through absorption of a photon. But the photon comes from a certain direction. I would expect that the wavefunction of the excited state ...
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If a polarized light wave is indistinguishable from its original self after being flipped 180°, why doesn't a photon have a spin of two?

The spin of a photon has a counterpart in classical physics, it's polarization, right? And if you spin a polarized light wave by 180°, (or pi radians), it is now the same as before, correct? So why ...
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How similar are phonons and photons?

If you go through the definitions for "phonon" (or for an explanation of phonon), most of the text or articles make the analogy to photons: A photon is a discrete quantum of light. A ...
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What is the length of a photon?

Some questions that look kind of similar have been asked before, and I find the answers quite confusing. I intend to ask this question in a way that clearly shows what I'm asking. Imagine the ...
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Does the atom get the impulse from a photon? [duplicate]

A photon has both impulse and energy. If it is absorbed in an atom from level E1 to E2 what happen to the impulse. Does the atom acquire the impulse of the photon? If so it would get some acceleration ...
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Why didn't the CMB clump into denser parts like the matter in galaxies with voids inbetween since the photons exert gravitational pull on each other?

There are other questions on this site about the CMB, but none of them answer my question specifically. I am not asking about fluctuations in the CMB. How could inflation affect the CMB? Now as far as ...
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Has the “spin” of a photon anything to do with a rotation movement?

If not, where does this denomination come from?
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What are the physical processes involved in feeling warm from the sunlight?

Suppose a human is lying on a beach. He/she starts to feel warm after exposing his/her skin to the sunlight. I assume that feeling is due to the ability of the human body of "measuring" the ...

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