Questions tagged [photon-emission]

This tag is for questions regarding to Photon Emission. Photons are emitted by the action of charged particles, mainly due to making a transition from a high energy state to a lower energy state. Although they can be emitted by other methods including radioactive decay.

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Is it possible to calculate ion species fractions from relative intensity optical spectra?

I'm trying to find references or instruction on how to calculate or at least estimate the ion population or population fraction from the optical spectra of a plasma. I have found tables that provide ...
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Why do electrons come to ground state even after giving absorbing energy?

Imagine you have a hydrogen placed under sunlight, now if we look at 1st shell of hydrogen, it has energy of $-13.6$ev now for 2nd shell we have energy of $-3.4$ev. 1st shell -> $-13.6$ev 2st ...
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Can Two Electromagnetic waves cancel each other if it 180 degree phase moving in same direction?

If we can send two electromagnetic waves -180 degree out of phase- in same direction, then the interaction of this wave with air molecules will be less due to the low intensity of the combination. So,...
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How exactly does one reaction of nuclear fussion exactly produce EMR of different types? [closed]

Electromagnetic radiation from sun is more likely produced by the nuclear fusion, and at a go radiation is released but how is it possible for different types of radiation to be produced such as, ...
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Helicity conservation during nuclear resonance in Goldhaber Experiment

Within the context of the Goldhaber Experiment. If a polarised photon of helicity $\pm 1$, is used to excite a $^{152}Sm$ Samarium nucleus to an excited state $^{152}Sm^*$, that then, by spontaneous ...
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Does each spectral line of an atom/molecule have a unique lineshape?

A spectral line is determined by a particular transition in an atom or molecule. In reality, this line isn't infinitely sharp, but has a small distribution about the resonance frequency as a result of ...
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Is refraction unpredictable?

Let us take a simplified version of refraction, where light slows down because of atom absorption and re-emission. Let us denote this time as $\tau_{emission}$, do we have a function $\tau_{emission}(\...
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Responsivity of a photo detector

I have a pn junction diode of which responsivity (R = Photocurrent / optical power) is to be calculated. For this purpose i have 5 LEDs of various wavelengths (UV, RED, BLUE etc). In this case, i ...
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Electrons in Atom in different energy states

I have a very basic doubt in Bohr's Atomic Model. I just studied that an electron can go to any Energy State with in the atom, by getting relevant energy from photons. If an electron goes to 2nd ...
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Will annihilation occur when two electrons and a positron are released at once to collide against each other?

suppose free Two electrons and a positron are released at once in space to collide against each other,will there be annihilation ?or there will be no annihilation due to imbalance of matter and ...
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Photoelectric emission at frequency less then threshold frequency

If I shine an EM radiation of frequency $\nu$ on a metal surface which has threshold frequency of $\nu_o$, where $\nu < \nu_o$ then, will the emission occur by multi photon absorption? My reasoning ...
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Thermally activated delayed fluorescence

In thermally activated delayed fluorescent (TADF) molecules, we consider 25% molecules in singlet first excited state and 75% in triplet, statistically, on electrical excitation after carrier ...
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Purcell effect for large cavities

The model of interest is a 2-level system (e.g. an atomic transition) inside a damped single-mode cavity. The purcell effect states that the atomic decay rate inside the cavity $\Gamma_{cav}$, on ...
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Terahertz generation in semiconductors after ultrafast laser excitation

Terahertz can be generated by means of the photo-Dember effect, where a short laser pulse generates electrons and holes. These charge carriers have a different mobility which gives rise to a dipole ...
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Selection rules for electronic transitions when noble gas atoms collide

The selection rules of atoms that are alone are useful for determining whether there can be certain radiative transitions, or which transitions are more likely than others. For example, for small ...
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Is the $(1s)(2s)$, $S=1$ excited Helium state metastable?

I am reviewing properties of atoms, and I am trying to understand the concept of forbidden transitions better. My understanding is mostly at the level of Griffiths quantum mechanics. My motivation is ...
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Where can I find data of a UV blocking glass absorption filter absorbing the visible light and re-emitting the energy as a photon of NIR?

If I understand correctly, a UV Transmitting, visible light absorbing colored glass absorption filter absorbs the visible light energy and re-emits it as near IR. On Oct 16, 2013 in How does Infrared ...
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Why does light behave differently when interacting with multiple particles?

When light hits an atom (I will use a carbon atom for simplicity), if it is not in the absorption and/or emission spectrum of carbon, it will simply pass through without interacting with the atom. ...
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Why does light not pass through opaque objects? [duplicate]

Since light is massless it does not interact with particles unless that specific wavelength is on the emission and absorption spectrum. The emission and absorption spectrum of an atom indicates the ...
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At what point of approach in annihilation process the charges of antiparticles disappear? How is relevant to the electron-proton interaction? [closed]

For me it is incomprehensible that from the indisputable fact that a free electron - like a proton - carries a constant charge with it, one transfers this empirical finding to bound electrons (protons)...
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What are the differences between electron-positron annihilation and proton-electron scattering?

To me, the beginning of the approaching of an electron-positron pair and an electron-proton pair look somehow the same. There is a spatial attraction and in the process there is an energy emission in ...
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How photon beam can be attained through Proton Accelerator?

I'm recently had been reading quite a lot about ADS and transmutation possiblity of Proton beam to neutralize nuclear waste. I came across with an Article from Big THINK https://bigthink.com/the-...
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Calculation of the rate of transition of the Hydrogen electron from $|2lm\rangle$ to ground state

This is how it was calculated in my book: We take the electromagnetic field to be part of the system. The initial state of the system is the direct product $|2,l,m\rangle \times |0\rangle$. $|0 \...
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How do objects emit light?

I recently bumped into a question of how things emit its color. And I've gone through some articles on the internet to be now stuck between two phenomenon: reflection (I'm not sure if its called this ...
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How can I find the light power of a polychromatic LED based on the minimum sensitivity of a photodiode array?

I'm building an optical sensor that scans a newborn baby's finger for diseases. I'll be using a polychromatic light (ie, white light) that will pass through the finger. There will be a diffraction ...
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Spectral Line Intensities of a sample

I am doing some research on the flame test and I get the main point. I was wondering, how do you calculate the rate of photons emitted vs frequency. When I look at the Sodium emission spectrum, There ...
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In a photoelectric cell, how come the electrons don't move to the higher potential through the vacuum without the need of an incident light?

I have been reading about the photoelectric effect and I have arrived at the photoelectric cell. Knowing that the air is removed from inside the cell, and assuming there's no incident light. How come ...
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Simple Quantum Electrodynamics question

First of all, what causes electrons to emit photons in QED? Why wouldn't electrons just not interact in that way Second question, how do electrons even get close enough to interact/exchange photons. ...
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Sources for emission spectra

I'm currently looking at a spectrum from a balmer lamp with clear lines for H-alpha through H-gamma. But there are additional, non-hydrogen lines at 774 nm and 842 nm. I assume that they are oxygen ...
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Collision Broadening - Spontaneous emission

I am currently reading Loudon's "The Quantum Theory of Light" and get stuck about the following sentence: Consider a particular atom radiating light of frequency $w_0$ . A train of ...
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What is the relationship between emissivity $\varepsilon$ and the imaginary part of relative permittivity constant $\epsilon^{''}_{\rm r}$ if any?

In terms of the Stefan-Boltzmann law a body that does not absorb all incident radiation emits less total energy than a black body and is characterized by an emissivity $0<\varepsilon <1$ such ...
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Is photon emission the time-reversed process of photon absorption?

Say we have an atom on which we shoot a photon. Is the process of absorption the time reversed process of emission? I can't imagine the two processes being the same, although in both cases the photon ...
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Photon Emission by Massless Fermions and Direction of Motion

In Peskin, a derivation about the radiated energy at low frequencies is given, as well as a derivation about the (mean) number of radiated photons. Both are found to depend on the differential ...
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Hamiltonian of a system of an hydrogenic atom in EM field

In an interaction between an EM wave and an hydrogenic atom (atom with single electron) we have in the semi-classical approximation (I think that's what is called, basically treating classically EM ...
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Forbidden emission lines [OI] in HerbigAe/Be

I am a beginer in astrophisics and I am studying HerbigAe/Be stars. I have read that this kind of stars have a circumstelar disc that emits in the infrared and that some of them presents emission ...
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What's the relationship between the emission spectrum and the material properties (refractive index, thickness)?

I'm currently working on the thermophotovoltaic problem. I have known that the emission spectrum of a single-layer structure is associated with the material properties, but I'm confused that the ...
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Why is spontaneous emission neglected in standard discussions of the two-level system?

When discussing two-level systems, spontaneous emission is often neglected `until later'. However, when discussed later, the two-level system is no longer discussed. For example, see Straten and ...
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In Compton effect, why is there a continuous distribution of wavelengths (including $\lambda$)instead of just $\lambda'$ for every fixed angle?

I was explained Compton effect as a collision between a photon and an electron that can be considered free. The equation is $\lambda' = \lambda + \lambda_c(1-\cos\phi)$ I've been reading more on the ...
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Comparing description of spontaneous absorption and description of stimulated emission

I am currently studying Diode Lasers and Photonic Integrated Circuits, Second Edition, by Larry A. Coldren, Scott W. Corzine, Milan L. Masanovic. Chapter 1.3 SPONTANEOUS AND STIMULATED TRANSITIONS: ...
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How does the photon detector in this experiment work?

https://www.youtube.com/watch?v=Cg7jMXQHxvM At 5:46 to 6:37 Dr. Aspect talks about photon detectors. At 6:10 he talks about firing single photons at a time, and having two detectors. From what I have ...
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Why do some electromagnetic waves have more than one photon?

I know that the energy of an EM wave is equal to nhv, where n is the number of photons, but why/how do the number of photons in a wave vary? If a single atom emits an EM wave with an energy of 100 ...
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Balmer alpha, beta line intensity

In different temperature environments, the intensity of the Balmer line is determined by the Saha equation and the Boltzmann equation. What I'm curious about is as follows. How can we measure the ...
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Why do spontaneous emission and absorption alone violate thermodynamic laws?

Einstein suggested that stimulated emissions must also occur along with spontaneous emission and absorption, because the latter two alone violate thermodynamic laws. How exactly do spontaneous ...
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How soon does an electron emit the absorbed photon back?

This question involves two cases: electrons bound to a nucleus and free electrons. Bound electrons Let's consider the hydrogen atom for simplicity. As far as I know, to be able to excite the electron, ...
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If atoms both absorb and emit photons, then why are there still gaps in an absorption line spectrum? [duplicate]

In my physics notes there is a section on line spectra, and describing how absorbance line spectra can by used by astronomers to find out what gases are present in a star, should it be emitting white ...
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Do atoms emit and absorb photons at the same wavelengths?

I know that atoms absorb photons, which promotes electrons to higher energy levels. Then upon de-excitation a photon is released. Is it true that the lines for absorption and emission spectrums are ...
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Why experimentally the Stopping Potential is affected by Intensity of light?

Experimentally we can se a little decay of stopping potential with decay of intensity. Why this happens?
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Absorption and emission spectra - regarding excited state of electrons

I had a question regarding the "excited state" of electrons. I know that electrons can jump up from their ground state to higher energy levels if given a specific amount of energy. But what ...
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Electron emission and photoelectric effect affected by intensity

It is said that when visible light is directed onto a metal surface, it doesn't emit electrons from the surface because intensity doesn't affect it. However, then it is said (relating to the equation) ...
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Electronic quantum jump time = transition time = lifetime?

Naively I assumed that an electron would sit in an excited state (in the shell of an atom) having some stochastic lifetime, so nothing changes and suddenly the electron would jump back into the ground ...

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