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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Denotation for entangled photon pair by SPDC process

I have a question regarding the eqaution of entangled photon pairs obtained in the type-2 SPDC process. The subscripts 's' and 'i' stand for signal photon and idler photon. And, the states 'H' and 'V'...
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Photon Catalysis

I am doing my research in the field of Quantum Optics. My topic of interest is Photon Catalysis. In this process, a coherent state and a fock state |1> are incident on the "a" and "b&...
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Since photons are said to be the force carrier of electromagnetic force, does it mean that photons get transferred from golf club to golf ball?

Just like it says in the question title. I have heard that photons are force carriers of electromagnetism. Is it not true, that when a golf club imparts force on to a golf ball, then the fundamental ...
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Special relativity particle creation

A photon hits a proton that is at rest (In the lab system) which creates a pion, so now there are only the proton and pion. The question is what minimal energy can you give a photon such that this ...
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CHSH Bell measurement, why is there difference between 45 and 135 degree?

Let assume BBO type-2 that simultaneously generates entangled photon pair in forms of horizontal polarization (H) and vertical polarization (V) of photon. One photon is going to Alice and the other is ...
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Does the energy of a photon change in different inertial systems?

Given a photon with energy $E$ is some system S what would be it's energy in a system S' with a constant velocity v relative to S? I have no idea where to start from. I think you need to calculate the ...
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If photons have also particle properties why should they not collide with each other?

If photons have also particle properties why should they not collide with each other? Collisions between fermions are possible as collisions between fermions and photons(bosons) except collisions ...
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Does the interaction between 2 photons change its traveling directions?

As I understand from the Hong-Ou-Mandle effect, the interaction between 2 photons is possible. Can 2 Photons interact with each other in free space? Suppose that the 2 photons met in the spacetime ...
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Are photons really 'particles' of light? [duplicate]

In Einstein's Photon Theory of Light, he proposed that light consists of distinct chunks or distinct packets of energy called photon and the energy of a photon is given by : $E=hν$ where $ν$ is the ...
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Can laser light be described by individual photons?

If laser light is described by a coherent state, a macroscopic quantum state, to what extent does it make sense to speak of individual photons in laser light? And if the laser is attenuated to be a ...
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Underlying principle of hydrogen lamp

I learned that a hydrogen lamp emits photons at specific spectral lines because of electrons falling from a higher energy level to a lower energy level.I think I understand this. However, nowhere can ...
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If a photon strikes a perfectly reflecting mirror, it is essentially at rest at the instant of collision. So why does the photon exist?

Photons can only move at the speed of light.how do we define its existence at the instant when it collides with a perfect mirror?
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Orbital Photon Speed at the equatorial plane of a rotating black hole

I've been trying to calculate $d\phi/dt$ of photons orbiting a Kerr black hole (Kerr metric in Boyer-Lindquist coordinates) on the equatorial plane, both counter and along with its rotation. So I used ...
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How to get a plan circular polarized wave [closed]

This paper contains a sketch with the description FIG. 1. When an absorbent disk A is placed in a plane circularly polarized wave L casting a shadow S. As in the questions title said, how one get a ...
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What is the basis of description of matter and energy in our universe in the form of wave and particle? [duplicate]

What exactly does wave particle duality mean does it mean that an electron is a particle which is moving like a wave or does it mean that an electron and a photon is neither a wave nor a particle and ...
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Confusion about the light and the transparency of objects

I am so confused about the interaction between the photon and the atoms especially when we see it and perceive the color. I think there are many questions like this before but I still don't understand ...
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How can a photon of a particular energy be supplied to a sample of gas to excite the electrons?

I have recently started reading about atomic spectrum of hydrogen gas. To excite an electron of a hydrogen atom the photon that collides must have exactly the same energy as the energy gap between the ...
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Two photons’ energy

Are two photons of energy $\hbar w$ the same as one photon of energy $\hbar 2w$? Edit: I'm asking this question because I'm reading about harmonic generation and in the contest of semiclassical ...
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Why do we assume that a photon has encountered only a single collision with an electron in Compton scattering

For explaining the experimental results of Compton scattering theoretically we consider a collision between a photon and a free electron and then calculate the new wavelength of photon after collision ...
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Can massless particles emit radiation? [duplicate]

Massless particles, be they gluons or photons (I can't think of no other), experience no time. How then can we say that they emit gravitons (to convey the information of their changing position to the ...
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Why shouldn't photons be able to curve spacetime? [duplicate]

I have read this question. It was asked if photons are able to curve spacetime. But if classical electromagnetic fields can curve spacetime (due to the energy contained in the fields contributing to ...
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is it possible to replace the welding machine with a light beam?

Using mirrors, lenses, and a battery of any power? Yes, it can be expensive, yes, it can be inefficient, but it is absolutely not important. Not about laser
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Is photon a wavepacket of electromagnetic field?

Photon is a "particle of light". Light is just a propagating EM field. Therefore photon is (at least intuitively) a localized EM field (i.e. wavepacket). In quantum optics, the Hamiltonian ...
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Unlike electrons, photons don't have a magnetic moment despite having a spin. Why?

DISCARD THE FIRST TWO PARAGRAPHS AND DIRECTLY READ THE LAST ONE. Electrons are charged particles and have a magnetic moment proportional to their spin. So they can respond to electric and magnetic ...
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How is the particle nature theory consistent with multi-photon photoelectric effect?

Under this question and answer discussion- https://physics.stackexchange.com/a/187562/297159 , how more than one photon can be absorbed by 1 electron has been explained briefly. However, if multi-...
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I think there has to be relation or dependency between Time Dilation and Light Emitted from an object (density of Photons)

"If you watched an object fall into a black hole, no matter how long you watched, you would never actually see the object enter it due to time dilation" There is something not adding up here....
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Photon temperature at nucleosynthesis

I've been asked about photon temperature at nucleosynthesis (3 minutes from Big Bang). So I guessed this is the moment when Matter and Radiation where in equilibrium: $$ \rho_M(T) = \rho_R(T)$$ Taking ...
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Phase/Intensity uncertainty relation

In quantum optic, we have the relationship: $$\Delta N\Delta \theta>1/2\tag 1$$ But to my knowledge, $\theta\in[0,2\pi[$ so $\Delta\theta$ is finite, then for example if we know perfectly the ...
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Diffraction Grating question/s

I wrote a little program to model a diffraction grating: Does a photon go thru every slit, or just a few, in an inch/es wide DG!? Do I treat a slit as just a single point source? Does a photon ...
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How is it that Increase in amplitude of electromagnetic radiation results in increase in number of photons

I cannot comprehend how the increasing of amplitude of an electromagnetic wave increases the number of photons. How does this even happen. I am also not able able to make sense of that fact that, when ...
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Coordinates of emission and reflection of a photon

Let $\gamma(s)$ be the worldline of a photon. In coordinates $x$ we have $x(\gamma(s))=(x^0(s),x^1(s),x^2(s),x^3(s))$ The tangent vector $V$ of the photon in this coordinates is given by $V=\dot{x}^a \...
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How are photons involved in electrical flow?

Lets say you have an extremely simple DC circuit with just a 9 volt ideal battery and a superconductive wire connecting one terminal to the other (don't do this on a real battery). Electrons flow ...
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Example where photon acts only as a wave

I've heard photon can act both as a wave and as a particle. In the photoelectric effect it acts as a particle. Is there any example where photon acts only as a wave?
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Why can't photons exceed the speed limit of the universe for a moving observer?

This question is somewhat stupid but it's intriguing me for a long time. In this question, the man was moving with a speed of $10$ $cm/sec$ physically (with his foot) as seen from an observer at rest ...
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Question about a single photon's wave

Assume you have a single photon generator in empty space surrounded by a spherical array of many detectors each of which is 10 light seconds from the generator. A single photon is generated. I ...
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For a two-level atom subject to a laser field, what is the rate of absorption followed by stimulated emission?

So the textbook I'm using (H.J. Metcalf and P. van der Straten. Laser Cooling and Trapping) derives the photon scattering rate of a laser close to a two-level transition starting from the Optical ...
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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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Phonons and Modes

I am trying to understand how normal modes, optical and acoustical cases and longitudinal/transversal propagation of waves are all together related. Lets say we are have a clystal chain (for ...
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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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