Questions tagged [photon-emission]

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Can inner electrons get excited? Can an already excited electron get excited again without first dropping to a lower energy level?

Is it only the valence electrons that can get excited or can the inner electrons get excited too? Plus, say for example can a electron of a hydrogen atom go from n=2 to n=3 without first returning to ...
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Relationship between the magnetic dipole of the electron and the polarisation of its radiation

When passing through a magnetic field, electrons are deflected sideways. This is the basis of the Lorentz force and all Hall effects. If this is done on a larger scale in particle accelerators or, in ...
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Is IR light emitted, rather than reflected?

When I look at an object in the sunlight, I'm looking at photons reflected back from the object. But if I wear infrared goggles and look at an object in the dark, am I looking at photons that are ...
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Why does spontaneous emission have larger spectral width than stimulated emission in a lasing medium?

What makes the stimulated emission's spectrum narrower than spontaneous emission's?
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If not fluorescence, what is the process of emission and absorption of white light by everyday objects?

An electron in an atom is excited by a photon and moves to a higher energy state. The electron then relaxes and transitions to a lower energy state emitting a photon of longer wavelength than that of ...
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Is it possible for a wavefunction to partially collpase?

What would happen in this situation: You have an ideal empty space with only two objects: a photon emitter, and a small observer. The emitter emits a photon in a random direction, with every direction ...
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Why do electrons in a cool gas not release photons as they are excited?

When white light is shone on a cool gas the electrons absorb photons of a certain wave lengths and become excited. Shouldn’t the electrons then return to ground and release photons with the same ...
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Random Direction of Spontaneous Emission, and Conservation Laws

I'm trying to imagine how/why the direction of a spontaneously emitted photon is random, and how that works and reconciles with the conservation of momentum and kinetic energy. For intuition, I was ...
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When can two electrons be excited in an atom?

In the National Institute of Standards and Technology's database, there is a table of the spectral lines produced by each atom in the periodic table https://physics.nist.gov/PhysRefData/Handbook/...
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Where do Photons in Hot “Box” Come From?

I've read through some related questions, like here, but these don't quite answer my question. Say I have an oven at room temperature, and I raise the temperature to 400 K. During this process, the ...
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Electron spin change and photon absorption/emission

I came across this document and would like to verify that I understand it correctly: My understanding is that only an electron with a negative electron spin can absorb a photon and thereby acquire a ...
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Why do we see a light “circle” in the Thomson Tube?

In the Thomson tube experiment, after the electrons have been accelerated, they enter a glass tube filled with a gas at low pressure. The tube is put between two coils that form a Helmholtz-coil. The ...
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Blackbody radiation vs spectroscopy

If a body (eg a metal) is glowing red hot then its temperature can be approximated solely based on the colour. But what if that colour is not due to blackbody radiation but due to excitation of ...
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Directionality of dipole radiation and spontaneous emission

I have a question on the directionality of the field radiated by an oscillating charge and the directionality of the spontaneous emission of say a two level atom. When I first started studying physics,...
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Why does the Sun's emission spectrum have missing lines?

I know it is because the electrons in hydrogen and helium absorb them however, they also drop back to ground state immediately and emit the previously absorbed photon. So there should be no net ...
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Why do photomultiplier tubes (PMT) require high voltage but silicon photomultipliers (SiPMs)/semiconductor photodiodes use low voltage for operation?

I have a PMT that requires 1000V for operation, but SiPMs, semiconductor photodiodes require only about 30V -- what fundamental feature causes this vast difference in operation bias?
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Is there an analogue to H-alpha emission in molecular hydrogen?

Balmer-alpha line emission in atomic hydrogen (i.e. H-alpha) corresponds to a wavelength of approximately 656 nm. As far as I can tell, in atomic deuterium, D-alpha emission is approximately the same ...
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How can energy conservation not be violated in stimulated emission processes?

Fermis golden rule, derived from time-dependent perturbation theory, give the rate for a quantum system, disturbed by a weak harmonic pertubation with frequency $\omega$, to transition from a state $|...
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Questions about sources of Infrared Radiation

Very simple question but I came across a website discussing sources of infrared radiation and it used an example to illustrate which objects emit more infrared than others. It said 'a candle flame ...
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In Franck-Hertz experiment, why mercury emits UV light while neon emits visible light despite neon having greater excitation energy?

The reference that I checked shows that Neon has an excitation energy of 18.2 eV, while mercury has 4.9 eV. However, the reference also shows that the wavelength emitted by the mercury is at the ...
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Balmer series for ionized lithium

I am trying to calculate the wavelength for the first spectral line in a Balmer-series for a two times ionized lithium, $\text{Li}^{2+}$. I know that the atomic number $z$ is 3 for lithium and it is ...
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What is the difference between Luminous intensity and intensity of illumination?

What is the difference between the Luminous intensity and intensity of illumination? Please explain with units and dimensions as well! I googled but I partially understood it!
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Understanding the derivation of photon noise from Bose-Einstein statistics

I will premise this question with the fact that I am trained in mathematics and not physics. Right now I am reading Chapter 1 of the book Optical Radiation Detectors about radiation noise in blackbody ...
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Can a photon's angular momentum couple to an electron spin, to cause a spin-flip (thus allowing intersystem crossings)?

Been reading up on intersystem crossing and have gotten rather confused by: a photon possesses an angular momentum of $h/2\pi$ so it can couple to an electron spin and in principle induce any ...
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Can X-ray diffraction be applied to liquids, gasses or non-crystalline materials?

I learned that X-ray diffraction happens due to the periodic arrangement of atoms in a crystalline material, so can X-ray diffraction studies be done on liquids and non-crystalline materials ?
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Where could I find the database of natural line widths for emission lines of elements?

I was doing a research to retrive Magnesium density from its emission line located at around 280nm. I was trying to fit the observed spectrum by the natural spectrum of Magnesium line (a bell curve I ...
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Rate of spontaneous emission and energy conservation

The english wikipedia article https://en.wikipedia.org/wiki/Spontaneous_emission#Rate_of_spontaneous_emission (26.08.2020, 16:45) gives the rate for spontaneous emission as $$ \Gamma_{rad}(\omega) = \...
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Is it always possible to infer photon distribution from photon statistics?

Say we are detecting light in the time interval $(t,t+T)$ that is described by the intensity $I(t)$. Let the integrated intensity in this interval be given by: $$U=\int_t^{t+T}I(t’)dt’$$ Since $I(t)$ ...
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Can you create high-energy photons using multiple low-energy photons? [duplicate]

I heard once that with a special crystal it's possible to "convert" somehow two green photons to a ultraviolet one and that some UV-lasers are based on this fact. Is this right, and even ...
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Momentum of photons

We know that photons (light) are massless but they have momentum. Now suppose I am in the space far away from planets/stars that there is no external force exerts on me, if: 1- I turn on a flashlight (...
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How can I tell if a photodetector is thermal noise limited or shot noise limited?

Most datasheets for photodetectors only specify the noise equivalent power, making no distinction between thermal noise (Johnson noise) and shot noise. For modelling purposes, how do I know whether ...
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Origin of black body spectra [duplicate]

As I understand it a blackbody spectrum is continuous – every possible frequency between the upper and lower bounds for that specific spectrum is there. When we look at the sun (mainly hydrogen) or a ...
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Colour temperature and emission spectroscopy

If blue light is emitted from excitations below 500C for example potassium in a flame emits purple photons but only has to be 500C for it to do so, then how do we know if the sun is yellow hot or if ...
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How does mirror create stimulated atoms in laser

I know excited atom can emit photon at any direction as long it stays consistent so the total angular momentum and spin states are conserved, this is spontaneous emission. What about stimulated ...
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Reconciling two descriptions of fluorescence

I am currently studying the textbook Infrared and Raman Spectroscopy: Principles and Spectral Interpretation, second edition, by Peter J. Larkin. Section 9. Selecting the Raman Excitation Wavelength, ...
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When does an electron release energy as photon and when as mechanical vibration?

Suppose we have a compound which has been given energy(either in the from of heat or light). Now, its electrons would absorb this energy and kick up to a high energy level. But, it would also re-emit ...
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$\text{He II}+\text{free electron}\to\text{He I}+\text{ photon}$ Photon emitted in this process belongs to $\mathrm{He}$ I spectrum or He II spectrum?

I know that He I means the unionized neutral Helium atom $\mathrm{He}$ and He II means the ionized Helium atom $\mathrm{He}^+$. The following table is a spectrum data from NIST (https://physics.nist....
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What rules govern the absorption of photons by electrons when the photons exceed the work function of the material?

I am currently watching a series of lectures on Nuclear Physics. One of the topics covered is the emission and absorption of X-Rays. This got me thinking about some of the physical chemistry I took as ...
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Integration over all directions in spontaneous emission, complex dipole element and polarization vectors

When calculating the rate of spontaneous emission in the Weisskopf-Wigner theory the time derivative of the excited state is related to a sum of couplings to all modes (directions and polarizations) ...
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Why is the transition $𝐽=0→𝐽′=0$ absolutely forbidden? Selection rules

I am still confused after reading this page: Selection rules in atomic physics . Why is $j' = 0$ to $j=0$ transition not allowed? What if the emitted photon has an orbital angular momentum? For ...
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Analysis of Angle resolved photoemission spectroscopy(ARPES) data

I was reading a thesis on ARPES and it's role. In one place, it was mentioned that ARPES is able to map the whole 4-dimensional momentum energy space for a given material. But to create a full 4-D ...
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Radiation Emission due to High Temperatures?

We know that an object emits radiation at all temperatures above absolute zero. But when an object is heated to high temperatures like the stars, Wouldn't it cause thermionic emission to take place? ...
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Is reflection just a re-emitted wavelength at the electronic scale? Does reflection require absorption in the first place?

I'm researching on how different wavelengths choose to either reflect, get absorbed, or transmit through a particular material. I've read that transmission is when waves do not interact with the ...
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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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Why on a $g^{(2)}$ measurement plot, we have multiple peaks for different values of $\tau$ (delay)?

Why on a $g^{(2)}$ measurement plot, we have multiple peaks for different values of $\tau$ ? I understand from "Hanbury Brown-Twiss intensity correlation experiment" that the value at $\tau =...
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Why can atoms only absorb/emit certain frequencies of light?

I'm aware that the orbitals of atoms have discrete energy spectra. The energies must obey the atom's Hamiltonian eigenvalue equation $H|\psi_n\rangle=E_n|\psi_n\rangle$ and this only holds for certain ...
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Does shaking an atom produce photons?

I have a vague recollection of a description of the relationship between matter and light. It went something along the lines of this: "Grab hold of a thing and ...
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How can the oscillating states of many atoms in a lattice combine to give even a larger number of possible states?

Basically, I was studying the band theory and there was that thing that I couldn't understand, and it appeared to be connected to another question: how is the blackbody radiation appear continuous ...
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What causes a double peak for a single wavelength when using an optical spectrometer system?

I am doing an experiment to determine the Rydberg constant for the Balmer series using an optical spectrometer system (consisting of a monochromator with a photomultiplier detector and pulse counting ...
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How do the electrons absorb energy in an discharge tube that is used for produce an emission spectrum?

When there's hydrogen in a discharged tube it produces an emission spectrum, emitting energy(photons). (Eg:-When an electron jumps from 3rd energy level to 1st energy level, the electron emits a ...

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