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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Does any colour appear white to our eyes if its emitted power is extremely large?

let's consider an ideal monocromatic source (for instance red) and let's assume you can regulate its emitted power without compromising its spectral "finesse". Start from 0 emitted W/sr. It ...
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Why doesn't the saturation photoelectric current depend on frequency?

From my understanding, even if the frequency of a photon is above the threshold frequency, it is not necessary that an electron gets ejected as the photon may have been absorbed by a metal atom ...
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Do gluons interact via virtual photons?

On a video on Youtube, I commented how a PBS Space Time episode helped me understand the speed of light by calling it the speed of causality. In response, I received the following comment: "Let'...
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Are Photons Entangled with Gravity? [closed]

Part 1: A photon's wavelength is red-shifted by expanding space. Since $E=hf$ the photon imparts some of it's energy to the curvature of space, slowing the expansion of space ever so slightly. Is that ...
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If a photon is massless, how can it be located at a point in spacetime? [closed]

It is quite common knowledge that a photon does not hold any mass i.e. it is massless. My physical intuition tells me that a "thing", in order for it to have a specific location in spacetime,...
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Integrating Planck's relation

By Planck relation, we know that an energy of a single photon is $E = hf$. If we are given EM-waves with interval of frequency $f_1$ to $f_2$, does integrating from $\int_{f1}^{f2} Edf$ $=\int_{f1}^{...
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Varying energy density of photons?

I know photon energy density is proportional to the fourth power of the scale factor, because it dilutes and redshifts. I want to take into account the added photon energy density from astrophysical ...
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Can the formation of a black hole in its infancy be explained by the following? [closed]

Can the formation of a black hole in its infancy be explained by the collision of a group of opposite-phase photons, that is, in opposite directions ? I wonder if you could make a black hole this way?
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Are all emitted photons accounted for at the detector(s) in the single-photon Mach-Zehnder interferometer?

Layman alert: I am sorry if I am asking stupid questions. I'm just trying to grasp what is happening with a single photon in MZ interferometer. Say we have a single-photon source, and let the second ...
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Is photon spin and polarization the same thing?

I have posted here regarding this before. I always get conflicting information when I research about this stuff. Some people say that a photon spins in or against it’s direction of motion…meaning if ...
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What happens to the information that a photon carries, when it interacts with another body that reflects, transmits, or absorbs it?

When a photon gets absorbed in a body, it transfers all its information to the body(what we call "being absorbed"). Now, it is the body that further processes the information and releases it ...
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Why are gluons color charged but not photon? Could there be a charged EM force carriers like gluons or neutral color charge carrier like photon?

Gluons have a color charge why don't photons have an electric charge like gluons?
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Does free carrier absorption lead to current?

The question is quite short: If photons are absorbed by free carrier absorption can one measure a current similar to a photocurrent due to photo electric effect?
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What is photon spin and polarization?

I have literally googled for hours on this subject. I am very curious on what spin really is and how polarization works for photons. I’ve read that photons have a spin of 1(no idea what that means or ...
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Where did I go wrong with quantum photon polarization?

J Murray answered a previous question with a proof of Bell's Inequality, and a description of it applying to photon polarization. I probably misunderstood the application to photons, so I want to get ...
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How do photons induce current in an antenna?

I have done a lot of research on this topic, but I have yet to find a good explanation in plain english (I’m dumb) that answered this for me. I know that photons have oscillating electric and magnetic ...
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What makes a photon a photon?

As i understand photons are excitation of the electromagnetic field. Therefore charged particles are affected by this excitation. But what if we have (highly theoretically) a particle that has the ...
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Phase shifts introduced by a beam splitter

I am studying this paper about the automatic generation of quantum experiments. The algorithm they are using is based on a series of symbolic transformations that are used to simulate the effects of ...
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Difference between Poincaré and Bloch sphere for single photons

The Bloch sphere is a geometrical representation of a two-levels quantum system, for example we can use it to represent the spin of a single qubit in the basis $\{\lvert H \rangle, \lvert V \rangle\}$....
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Is Bell's Theorem Wrong?

Sorry for the provocative title. There's probably something wrong with my reasoning, and maybe someone will bother to point it out. I did not understand Bell's Theorem, so I looked for easy ...
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What happens after an atom releases a photon in laser cooling?

I am a high school student trying to understand how laser cooling works. What I understand so far is that scientist take a bunch of atoms in vacuum and point lasers at them from all directions. The ...
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Is this an example of a spatially coherent wave?

My ultimate goal is to understand why the spatial coherence of a wave increases with distance from the wave source. From what I have read though, there seems to be conflicting definitions of spatial ...
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If an atom has 'infinite energy levels', how does the photoelectric effect exist?

I don't quite get claims that an atom has 'infinite energy levels'. The photo-electric effect tells us that if photons of a certain threshold of energy are absorbed, the electrons will be freed from ...
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Is the distance between photons the wavelength of light? [closed]

I have a question that may be naive for you, but I would like you to answer it The question Is the distance between photons the wavelength of light?
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Feynman's view about light

Professor Feynman, in his “QED: The strange theory of light and matter”, states at page 15: “I want to emphasize that light comes in this form - particles. It is very important to know that light ...
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If the photon hasn't an electric and magnetic field yet, then what does its polarization vector stand for?

In the context of quantum electrodynamics, The photon field is described by a operators connected to a Fock space of photon states $e^{-ip_{\mu}x^{\mu}}$. The relativistic photon wavefunction can be ...
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Is the electric field the same as probability amplitude of a photon?

I am a novice in Quantum Mechanics and have seen many authors interchangeably using the two terms in the introductory textbooks. But I have never seen it written explicitly anywhere 'The probability ...
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Can electrons absorb photons?

I see two broadly opposite answers to this question. One is that electrons can absorb photons, and one is that electrons can't absorb photons (see How many photons can an electron absorb and why?). ...
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Where does light come from in electron transitions?

So when we use light bulbs ... The heat excites an electron The energy makes the electron go to a higher orbital - higher energy level The electron comes back to a lower energy state Light is emitted ...
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How can photons have an electric field without having a charge?

I've been reading up on photons, and find myself puzzled by an element of them... How can photons have an electric field without having a charge? Correct me if I am wrong but I believe electric fields ...
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Is there a probability that a neutrino and anti-neutrino transform into two photons?

A neutrinos and an anti-neutrino can meet, form a virtual $Z^0$, which subsequently can create a new pair of leptons. Now, an electron-anti-electron pair can do the same, but they can create two ...
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Inertial frame of reference in special relativity

How could we measure rest mass of photon (that would be zero) when we agreed that photon can not be a inertial frame of reference (because of the dominator of Lorentz's transformation)?
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How did Einstein calculate the wavelength of photons?

Einstein's Photoelectric equation states that $$h\nu = h\nu_0 + \frac{1}{2}mv^2$$ which uses frequency. But if he assumed light to be a stream of particles how would he calculate it's frequency? de ...
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Phototcurrent illuminated gold plate

Let's say we have a gold plate connected to a current meter and illuminate the plate. How would you calculate the photo current? My first idea was to check the ionization energy of gold $E_{ion}$ and ...
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Maxwell equations associated to a massive photon

Since the photon has no mass, longitudinal electromagnetic waves cannot exist, and ordinary electromagnetic waves are always transversal waves. However, by speculating a bit we could introduce in the ...
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Frame of reference of a photon [duplicate]

I'm curious about the fact that it is impossible to consider a frame of reference where a photon is the reference itself (meaning a frame of reference where this photon can't move). I looked for ...
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Is photon redshifted if observer starts moving away after photon is released

A. A light source and an oberserver are stationary relative to each other. The source emits a photon and the observer measures the wavelength. B. A light source and an observer are stationary ...
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Explanation for few things in this paper about photonic crystals

In this paper two weakly coupled cavities are excited with light. Their frequencies are modulated by a mechanical pulse. I have the following questions: What is the Hamiltonian of this system ? I don'...
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How to mathematically express and then optimize my photon emitter? [closed]

A laser shoots photons directly at a flat disk with a fixed linear rate f(t) on the interval [t0=a,tn=b] with a horizontal path. E.x. f(t)=100 photons per second The laser is controlled by robotic ...
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Probability of vertically polarized photon passing through a polarizing lens at an angle of 60∘ degrees from horizontal

Textbook says if a photon has vertical polarization. When it hits the polarizing lens making an angle of 60∘ with the horizontal, the likelihood that the photon passes through is 75%. How is 75% ...
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Band theory of Photonic crystals

I have a basic question about the band structure of photonic crystals. If I have a periodic potential, then Bloch-theory tells me that the bands yield the energy spectrum of the Hamilonian which is ...
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How to disentangle two entagled particles (photons) without distroying anyone?

Can a twin photon pair entagled in polarization get disentangled after one of the photons meets a PBS (polarization beam splitter). I suppose after the PBS the photon will go one way or another ...
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Why do we use tin in extreme ultraviolet (EUV) lithography?

I am in awe of what we have achieved with EUV light, and like to think about it in my free time. One question that I have is: What are the calculations that point us toward tin as the best EUV light ...
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Are photons the sources for the electron field?

I'm self-learning QFT, so please excuse my inaccuracies. Consider the complete quantum electrodynamic action: $$\int d^4x \bar{\psi}(i\gamma^\mu \partial _ \mu - m)\psi + A_\nu J^\nu - \frac{1}{4}F^{\...
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Why using incorrect formula results in a correct formula? [duplicate]

I know that the mass of a photon is zero. However, others say no it is just the rest mass which is zero, the relativistic mass isn't, but I say that no it is also zero because the rest mass $m$ is ...
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Photons in communications theory

In engineering communications theory we switch between time and frequency domain interpretations. If a pulse centered at frequency F is shot out of a transmitter, it's limited time duration implies ...
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Why does the Planck curve drop below the Rayleigh-Jeans curve for blackbody radiation when Planck quantized the energy?

This has been a research topic of mine for days now. I understand the Rayleigh-Jeans law and how it leads to the ultraviolet catastrophe. I have been searching for a clear, conceptual explanation of ...
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Do EM waves cancel out permanently in this example?

If we emit two photon rays one from each source 1 and 2 and after they reflect on mirrors to reach the same trajectory they should cancel out in the case their phases are opposite 100% but will any EM ...
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What is virtual photon concept in classical electrodynamics?

If we observe a charged particle like an electron passing us at some high speed $u$, then as $u \to c$ the field we observe looks like a superposition of plane waves normal to the trajectory of the ...
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Speed of light exiting a prism [duplicate]

When light travels through a medium, even a sparse medium, it slows down from the speed of light in vacuum to the speed of light in that medium. When that light re-enters a true vacuum, it will resume ...

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