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3
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1answer
48 views

How many photons are there in free space on average

Estimates of the amount of for example "dark matter" are of interest to the cosmologists. However, I have never seen an estimate of how many "free" photons could be speeding about in the known ...
2
votes
1answer
52 views

Can an absorbed photon be emitted as two photons?

I am taking an intro to astronomy class, and have touched upon absorption and emission lines and etc, the prof asked this question in class and got me thinking. I would want to say no, because one ...
2
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0answers
54 views

Estimating temperature with Boltzmann relation with split emission lines

I'm trying to estimate the temperature of a plasma through the use of hydrogen lines, $H_{\alpha}$ and $H_{\beta}$ using the Boltzmann relation: $$ \frac{ n_{2} }{ n_{1} } = \frac{ g_{2} }{ g_{1} ...
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0answers
32 views

Emission of photon in space [duplicate]

A source is emitting photons towards all directions. An observer sitting at millions of light years away can receive the photon from all the places. There will be infinite directions from where the ...
0
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0answers
37 views

What are the properties of the electromagnetic radiation from a magnetron?

There are different modes of EM radiation. A bulb emits photons in a wide range of wavelengths and without polarisation. Radio waves are polarized modulated radiation. What is about the radiation ...
1
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2answers
32 views

How does different particle size account for different colors?

I understand how objects have color in terms of absorption and reflection; however, in stained glass, various nano-particles can have different colors depending on the particle size. As described in ...
1
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1answer
21 views

Mossbauer effect - Deriving the recoil energy formula

I am working on a problem that deals with the Mossbauer effect and calculating the recoil energy on a iron-57 atom, initially at rest and excited to 14.4 keV, after it emits a photon. In the Wikipedia ...
1
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1answer
40 views

Bandgaps of Silicon and their application in active optical elements

I know that silion has an indirect bandgap at $E = 1.12 \, eV $ or $ \lambda = 1.107 \, \mu m$ and I have read that active optical processes like absorption and emission have a decreased likelihood to ...
0
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0answers
20 views

What does “at%” refer to in sol-gel method?

I'm reading on the preparation of ZnO thin films for UV stimulated emission and I found a method called Sol-Gel. During this I found a paragraph saying, " the ratio Ag/Zn in the sol is 3 at%......". ...
0
votes
1answer
29 views

When light is reflected, if some of the light is absorbed in the particle, does it change the particle?

Which color/frequency of the light is absorbed and which part is reflected? How is it determined which part will be absorbed? Does that depend on the particle? N.B: When I say particle, please keep ...
1
vote
2answers
195 views

Atomic natural line width

In laser cooling, with a model of a 2-level atomic system, spontaneous emission is stated to be dependent on the "natural line width" of the excited state of the atom. This width is defined as the ...
2
votes
2answers
69 views

During the “Dark Ages” of the Universe's evolution, how lumpy (anisotropic) and dynamic was the mass distribution?

In the dark ages between recombination (~0.4 Myr post-BB) and reionization (~300 Myr post-BB) of atoms, there was not any condensed-phase matter (except maybe some form of dark matter), nor radiation ...
2
votes
1answer
55 views

Why is stimulated emission necessary for detailed balance?

Detailed balance says that in equilibrium, the total number of particles leaving a certain quantum state per unit time equals the particles arriving in that state per unit time. Now, without the ...
1
vote
1answer
117 views

How did Einstein know that it was necessary to include “stimulated emission”?

How did Einstein know that it was necessary to include "stimulated emission" which was in the same direction as the incident photon and in phase with it?
0
votes
1answer
47 views

What is supposed to be used as $m$ in $m\lambda = d\sin \theta $

I know that $m$ is the "order number", but I don't understand how this applies to the lab we did. We looked at Hydrogen gas through a diffraction grating (500 lines/cm or something like that) and saw ...
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0answers
103 views

Why wouldn't any Emission Theory work?

http://www.pitt.edu/~jdnorton/teaching/HPS_0410/chapters/origins_pathway/#Emission Here, at the Emission theories of light, I loved the discussed theory. There seems to be a contradiction right ...
0
votes
1answer
38 views

Semiconductors light emission

Suppose a pure semiconductor, with a direct gap. If I apply a constant voltage to it the electrons will jump to the conduction band. So when I turn it off will it emite light?, because the electrons ...
0
votes
4answers
807 views

Spectral line formula

Two years back my friend told me a simple formula for calculating the number of spectral lines. But, now I'm a bit confused about it number of lines is =$ \frac{2(n-1)}{2}$ is this right or is there ...
2
votes
1answer
94 views

Probability of photon emission

If a photon of a given wavelength is absorbed by an electron (for simplicity, let's assume the electron has only one excited state), does the probability that the electron jumps to its excited state ...
0
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2answers
68 views

Is shape of a black body much of a concern in physics?

When I read a book on computer vision, I stumble upon the ideal black body model. Using Lambert's cosine law (wiki), one is able to compute the intensity of an area element dA w.r.t. some observer. ...
1
vote
1answer
68 views

Spectral lines and QM

In the various presentations I've seen so far in atomic physics of series such as the Balmer series, the wavelength of each spectral line is definite - but in QM, free particles have no definite ...
2
votes
2answers
45 views

Can a fluorophore emit a higher energy photon than it absorbed

It is unclear for me what processes are exactly in place during the absorption-reemission process of a fluorescing photon. I am thinking about the case when the absorption and emission spectrum ...
1
vote
1answer
340 views

Work function definition

As in this post How would I calculate the work function of a metal, the definition is given by "the minimum thermodynamic work (i.e. energy) needed to remove an electron from a solid to a point in the ...
0
votes
1answer
170 views

One photon and two electrons

Since an absorption of one photon by two electrons was experimentally noticed when one photon excites two atoms in touch, should we accept even an emission in common of one photon by two electrons?
3
votes
1answer
450 views

In how many possible ways can a photon be emitted?

I am currently studying atomic physics, and I encountered the question above. I am posting this question because I can't afford to move on with even the tiniest bit of uncertainty in my understanding ...
16
votes
3answers
303 views

Does the diffracted electron radiate photons?

When electron is diffracted after the slit it might follow different direction, than before the slit. That means, that going through the slit it gains some acceleration. And accelerated charge emits ...
0
votes
1answer
81 views

photon absorption and emission

I was reading a book (Sears Zemansky) about this subject but I didn't understand something of an example, and this is that according to me there should be a process of emission for each of absorption ...
0
votes
1answer
58 views

What is “Lifetime Intensity” in photoluminescence?

I'm reading an article "Surface plasmon enhanced Förster resonance energy transfer between the CdTe quantum dots". Link The reasearchers are writing about increase in "lifetime intensity" and even ...
0
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0answers
48 views

When optically pumping a lasing gain medium with another laser, does Stimulated, or Spontaneous emission dominate?

Much of my reading seems to indicate that laser pumping results in a fluorescent stokes shift but somehow photon vector is maintained. I've seen the phrase "Spontaneous Fluorescence by Stimulated ...
1
vote
3answers
305 views

Do electrons in absorption spectra absorb photons with enough energy to release them from their parent atoms?

Absorption spectrum theory says that electrons in the atoms absorb only photons of certain frequencies, which causes the dark lines in an absorption spectra. However, I understand that electrons that ...
7
votes
0answers
253 views

Integration & bremsstrahlung calculation

In this paper (relevant pdf section) that I'm reading, involving the calculation of bremsstrahlung in electron proton scattering (diagram below), the author calculates the integral over outgoing ...
1
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0answers
67 views

Spontaneous parametric down conversion and relative time of emission of two entangled photons

A pump beam excites a non-linear crystal which produces two entangled photons with perpendicular polarization, namely in the state $|HV>+|VH>$. Are there examples where one of the photons was ...
2
votes
0answers
57 views

How does a photon travel through an electron cloud?

We all know that the exact position and exact velocity of an electron in an atom cannot be determined simultaneously, as per the Heisenberg uncertainty principle. We only talk about the probability of ...
6
votes
3answers
330 views

What if all the electrons leave a metal?

I was studying photoelectric effect. Then I thought that what will happen if all the electrons from a metal piece come out as photoelectrons by using a light source of particular frequency? Will the ...
3
votes
1answer
102 views

What is the frequency of a photon emitted by an accelerated charged particle?

When a charged particle is accelerated by a field, it would seem there are many possible photons that could be emitted to obey conservation of momentum. Is it random, or time-dependent, or based on ...
2
votes
3answers
124 views

Photon speed going from $0$ to $c$ initially? [duplicate]

I have read many questions which ask whether there can be photons at speed other than the speed of light and all of them are answered no! But when the photon is created for ex during electron ...
3
votes
3answers
228 views

Stimulated emission and No cloning theorem

I have a little trouble with the simulated emission. I know of the no-cloning theorem which states that it is not possible to duplicate any state. One the other hand, I know about the stimulated ...
3
votes
1answer
92 views

Using the fine structure constant to measure atomic and molecular sizes

This is kind of a coursework question but it bring up some really interesting things about the fine structure constant $\alpha$ so I wanted to post it to not only make sure I understood something but ...
7
votes
2answers
431 views

Why does Pyrex glow orange under UV?

In a Physics lesson today our teacher performed a demonstration to show how quinine in tonic water glows blue when under UV light. He showed us the same demonstration using water in a Pyrex beaker, ...
3
votes
2answers
66 views

How do molecules bubble off a photon?

After being excited by a photon, an electron of a photoactive molecule jumps to a higher electronic state. When it relaxes, the molecule emits a photon (in simple terms). How is this photon ...
5
votes
3answers
501 views

Acceleration of electric charges and radiation

According to classical electromagnetic theory, accelerated charges should emit radiation and lose energy. The reason given in my book why atoms don't emit radiation (say, when the atom moves along a ...
1
vote
1answer
44 views

Excited Energy levels of Hydrogen vs Solids

My question has to do with Excited Energy Levels. I keep reading and learning that all objects/most solids emit infrared radiation. But to emit radiation, an object's particles must first enter a ...
0
votes
1answer
72 views

Does firing electrons at an object change its colour?

If one had an electron gun capable of firing electrons with a specific energy at an object, can it change its colour? I think it is possible because the emission spectrum of the material would ...
1
vote
1answer
56 views

Visible Lines for Hydrogen

Say H atoms are excited to 4th level, n=4 that is, how many lines do we see? How to decide the number of the lines?
1
vote
1answer
591 views

Calculating laser wavelength/power to cause emission of light in a gas?

I've become interested in volumetric displays. In particular I'm looking at a pair of lasers scanning a volume of gas such that the intersection of the lasers would supply enough energy to cause the ...