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209 views

Times associated with Absorption and Emission Processes

I am currently reading the book "Advances in Atomic Physics: An Overview" by Cohen-Tannoudji and Guéry-Odelin. In pages 29-31 the authors discuss a two-level atom subject to a broadband radiation ...
1
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3answers
118 views

Radiation pressure and conservation of energy

TL;DR: How can radiation pressure conserve energy, if we consider the case where the atom absorbs all the Energy of the incident photon via its newly excited electron, and stills gains additional ...
0
votes
1answer
43 views

Raman effect and IR absorption

Let's consider a molecule with N atoms, on which is shot a polychromatic IR beam. From the quantum selection rules, we know that in a single event of absorption only one of the 3N-6 oscillators can be ...
1
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0answers
44 views

What is the difference between upconversion and two photon absorption?

I have read this: https://en.wikipedia.org/wiki/Photon_upconversion And it says that upconversion is a process where subsequential absorption of two or more photons leads to emission of light with ...
1
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2answers
98 views

What happens if we re-excite an excited electron to a higher energy level?

What happens if we re-excite an excited electron to a higher energy level? e.g. we excite hydrogen's electron from n=1 to n=3, then before it gets to return to the ground state, we hit it with ...
1
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1answer
113 views

What is the meaning of a Fourier Transform in an electric field $E(\omega,t)$?

There is this electric field in one dimension: $$ E(\omega,t) = E_0 \cos(\omega t) $$ It is reaching the surface of a semiconductor. The number of photons reaching the surface per unit of area is ...
2
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0answers
49 views

given an AC field, how many photons are there?

Say you are applying a time varying potential across double quantum dots in the form of $V_{ac}$cos($2\pi f t$). We know that each photon has an energy $E_{photon}= hf$. Is it correct to say that ...
1
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2answers
68 views

Does photon absorption annihilate the associated EM wave instantly?

My Understanding A single photon has an associated electromagnetic wave. The wave is spread out in space, but the photon is considered a point particle. If the photon is absorbed, the entire wave ...
2
votes
2answers
130 views

Absorbtion of photon

Electrons in an atom absorbs an incoming Photon to gain energy and jump to a higher energy level (shell or different orbital) considering the fact that the photon doesn't have enough energy to make ...
1
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1answer
120 views

Is there a connection between the frequency of a photon and the oscillation frequency of the atom which absorbs it?

If a photon has energy $E$, we know it has angular frequency $\frac{E}{\hbar}$. If an atom has an energy gap $E$ between its ground and first excited state, we know that if the atom is in a ...
7
votes
3answers
505 views

How precise must the energies match for absorption of photons?

According to Quantum Mechanics, in order for an atom to absorb a photon the energy of the photon must be precisely that of a "jump" between energy states of the atom. How precise must it be? If I ...
12
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1answer
1k views

How does one account for the momentum of an absorbed photon?

Suppose I have an atom in its ground state $|g⟩$, and it has an excited state $|e⟩$ sitting at an energy $E_a=\hbar\omega_0$ above it. To excite the atom, one generally uses a photon of frequency $\...
2
votes
1answer
1k views

Is the Energy of an absorbed photon exactly the energy of the band gap?

I was wondering, if the Energy of a Photon which is absorbed by an Electron, hast to be exactly the Energy of the bound gap. So if i have two energy levels in an atom $E_2$ and $E_1$, does my ...
19
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3answers
3k views

Why do lines in atomic spectra have thickness? (Bohr's Model)

Consider the atomic spectrum (absorption) of hydrogen. The Bohr's model postulates that there are only certain fixed orbits allowed in the atom. An atom will only be excited to a higher orbit, if it ...
1
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1answer
125 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 ...
3
votes
4answers
549 views

How can we prove that a photon is absorbed only once?

When I first heard about the photons and the double-slit experiment my immediate thought was the following: Alright, energy is not absorbed continuously but in discrete units, photons, but nature ...
2
votes
2answers
1k views

How to connect Rabi frequency with absorption intensity?

If a particle with non-degenerate spectrum starts in some eigenstate, and the frequency of the external EM field matches some transition frequency, then this would lead the particle to do periodic ...
1
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0answers
222 views

Absorption Spectrum

I just learnt what absorption and emission spectrum are. And our teacher introduced us to what Quantum Dots are. And showed us their absorption and emission spectra. And they look something like this ...
3
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2answers
674 views

Photons and Absorption

Hello and thanks for reading my question: Imagine we send one photon at an atom, and it happens to be the right frequency such that it gets absorbed fully by an electron in this atom. Obviously that ...
3
votes
1answer
115 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 ...
3
votes
1answer
851 views

When an electron absorbs a photon doesn't that change it's mass?

When an electron absorbs a photon it leaps to a higher energy level, what exactly happens when an electron absorbs a photon? By the mass-energy equivalence doesn't that changes the electron's mass and ...