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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Can a photon be detected by a “lateral” detector?

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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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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Is colour a purely quantum effect?

If the colour of an object is determined by the wave-lengths of light that is absorbs and reflects (?) then can colour be described as a purely quantum effect (i.e. without quantum effects an objects ...
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Is it possible to confine a photon in less than its* wavelength?

*(Its, or associated. That is somehow the question). I can think of, at least in principle, a perfectly reflecting optical cavity with dimension comparable to the wavelength of the electromagnetic ...
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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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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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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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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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What happens when a photon hits a mirror?

When a photon of light hits a mirror does the exact same photon of light bounce back or is it absorbed then one with the same properties emitted? If the same one is bounced back does it's velocity ...
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Conservation of Mass during Electron - Positron Annihilation

An electron has a mass of $m_e = \; 9.1094 × 10^{-31} kg$. A positron has the same mass. So during electron positron low-energy annihilation, won't the law of conservation of mass be violated? Note: ...
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How can sub- and super-Poissonian statistics be distinguished from bunching and antibunching?

This is my first post here, so I apologize if there's something wrong. I am studying quantum optics and I found myself in trouble with the difference between bunching/antibunching and super poissonian/...
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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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Laguerre–Gaussian (LG) mode and vortex light [closed]

Why is Laguerre–Gaussian (LG) mode has centre singularity and vortex light has the centre singularity, what is difference between them ?
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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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Cases wherein electrons do not follow “all or nothing” principle

The Wikipedia article on photoelectric effect has the following line: Electrons can absorb energy from photons when irradiated, but they usually follow an "all or nothing" principle. All of the ...
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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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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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Source of Light bending [duplicate]

Even though I’m familiar with quantum mechanics, I’m unfamiliar with general relativity, so I hope for an explanation simple enough that I can understand. As far as I know the following three (...
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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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If photons have no mass, how can they have momentum?

As an explanation of why a large gravitational field (such as a black hole) can bend light, I have heard that light has momentum. This is given as a solution to the problem of only massive objects ...
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What factor decides that when will scattering happen and when will reflection?

I don't understand what is the difference between Scattering and reflection? I have searched and found that in scattering, the atom absorb and re emits the photon, while reflection is due to particle ...
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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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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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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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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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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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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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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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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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Photons and Electric Current

I am trying to understand how photons as the force carrier for the electromagnetic force (or field) manifest themselves in a flow of electric charge, i.e. an electric current. Both standard (...
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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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Can photons be detected without being absorbed?

I am thinking about a detector that would beep if light passes through it. Is it possible?
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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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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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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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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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Single photon interferometry

I am always surprised by the subtleties that are embedded in the wave/particle dualism. That is why I read again and again the paragraph in the Dirac's classical text dealing with the single photon ...
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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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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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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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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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Is the source of electromagnetic radiation exclusively the excited subatomic particle? [closed]

The treatment of EM radiation without including the topic of photons is successful. Just as the description of thermal processes works without the inclusion of the atomic level. Or the gas theory. But ...
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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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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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Why is the GZK cutoff at such high energies?

Why is theGZK cutoff at such high energies? The threshold energy for Compton scattering is 0.511 MeV. But the inverse Compton scattering has a very high energy threshold. For example in ...
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Is Photon BEC possible in planar cavity?

It is well known result that Photon BEC was achieved in slightly curved cavity, because curved mirrors provide trapping potential (https://www.nature.com/articles/nature09567). We can see that this is ...

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