Probe absorption and dressed states

In summary: So the probe absorption is still slightly nonzero, even with a strong pump. That's because the pump is not 100% absorbed. Some of the pump will be transmitted, and some of the probe will be absorbed.I see! So, the probe absorption is not zero for ##\Omega = 10 \Gamma## because the pump is not 100% absorbed, and this means that the atoms will absorb some of the probe, too. But for ##\Omega = 0.3 \Gamma##, the pump is 100% absorbed (because it has small power), and this means that the atoms won't absorb any of the probe, because there are no atoms left in the ground state (since they are all excited by the pump
  • #1
BillKet
312
29
Hello! I am reading about dressed states, and I am presented a situation in which we have a laser (the pump laser) on resonance with a 2 level (atomic) transition, and a second, weak laser (probe laser) that is scanned over a frequency range. The absorption spectrum of the probe laser, for different Rabi frequencies, ##\Omega## of the pump laser is shown in the attached figure. My question here is only for the case of ##\Omega = 0.3 \Gamma##. Given that we have atom laser interaction, the ground and excited state of the atom ##|g>## and ##|e>## are not eigenstates anymore. The eigenstates are, for zero detuning (##\Delta = 0##) ##|+> = \frac{|g>-|e>}{\sqrt{2}}## and ##|-> = \frac{|g>+|e>}{\sqrt{2}}##. So, the actual levels that the probe laser sees are ##|+>## and ##|->##. Given that the pump laser has a small power, the ground atomic state, ##|g>## will be more populated than the excited one ##|e>## (i.e. the population won't be split 50/50 as it would be for high laser power) in the steady state. However, the ##|+>## and ##|->## and equal linear combinations of ##|g>## and ##|e>##, so they should have equal populations. I also attached a little drawing with the levels and populations (populations are draw as circles, with bigger circles meaning bigger population). The 2 levels connected by the wiggly line represent 2 levels that can be connected by the probe laser, assuming the probe laser is on resonance. What confuses me is: why do we get an absorption at all (according to the first figure) when the probe laser is on resonance. According to the second figure, the 2 levels connected by the probe laser (wiggly line) have equal populations (even if ##|g>## and ##|e>## have different populations)? Shouldn't the absorption be zero, given that the amount of absorption and stimulated emission would cancel each other? Can someone help me understand what am I missing here? Thank you!
Screen Shot 2021-04-04 at 1.22.59 AM.png


Screen Shot 2021-04-04 at 1.31.59 AM.png
 

Attachments

  • Screen Shot 2021-04-04 at 1.31.59 AM.png
    Screen Shot 2021-04-04 at 1.31.59 AM.png
    16.3 KB · Views: 135
Physics news on Phys.org
  • #2
Sorry for an overly brief reply. Crazy week!
BillKet said:
Shouldn't the absorption be zero, given that the amount of absorption and stimulated emission would cancel each other?
You have the right idea, but remember that the atom doesn't differentiate between pump laser power and probe laser power. It won't totally ignore the probe in favor of the pump. There will be competition between the two. Some of the probe will be absorbed and re-emitted, and a little bit less of the pump will be absorbed and re-emitted.
 
  • #3
Twigg said:
Sorry for an overly brief reply. Crazy week!

You have the right idea, but remember that the atom doesn't differentiate between pump laser power and probe laser power. It won't totally ignore the probe in favor of the pump. There will be competition between the two. Some of the probe will be absorbed and re-emitted, and a little bit less of the pump will be absorbed and re-emitted.
Thank a lot! So basically, when the pump has low power, we need to account for the probe laser, too (i.e. we would need to solve the optical Bloch equations with 2 lasers present). If the pump has a big power (as in the case for ##10 \Gamma##), the effect of the probe will be so small that we can use the dresses state picture intuition, as if the probe was not present, and this is why we actually have zero absorption on resonance for ##\Omega = 10 \Gamma##.
 
  • #4
Yep! The effect of the probe laser on the atom population is small, but the effect of the pump on the probe spectrum is ginormous, as shown in the graph.
 
  • Like
Likes BillKet

Related to Probe absorption and dressed states

1. What is probe absorption?

Probe absorption is a phenomenon in which a probe beam of light is absorbed by a material, causing a change in the material's energy state. This absorption can be used to study the properties of the material, such as its chemical composition or electronic structure.

2. How does dressed states affect probe absorption?

Dressed states refer to a phenomenon in which an atom or molecule is coupled to a strong electromagnetic field, causing a splitting of its energy levels. This can affect probe absorption by changing the energy levels available for the probe beam to interact with, resulting in changes in the absorption spectrum.

3. What is the significance of studying probe absorption and dressed states?

Studying probe absorption and dressed states can provide valuable insights into the behavior of atoms and molecules in different environments. It can also help in understanding the interactions between light and matter, and has applications in fields such as spectroscopy, quantum optics, and quantum information processing.

4. How is probe absorption and dressed states measured?

Probe absorption and dressed states can be measured using various techniques, such as absorption spectroscopy, Raman spectroscopy, and fluorescence spectroscopy. These techniques involve shining a beam of light onto the material and measuring the changes in the transmitted or emitted light, which can provide information about the material's energy levels.

5. What are some real-world applications of probe absorption and dressed states?

Probe absorption and dressed states have numerous real-world applications, including in the development of new materials, understanding chemical reactions, and studying the properties of biological molecules. They are also used in technologies such as lasers, solar cells, and medical imaging devices.

Similar threads

  • Atomic and Condensed Matter
Replies
6
Views
2K
  • Atomic and Condensed Matter
Replies
1
Views
1K
  • Atomic and Condensed Matter
Replies
3
Views
1K
  • Atomic and Condensed Matter
Replies
13
Views
3K
  • Atomic and Condensed Matter
Replies
8
Views
2K
  • Atomic and Condensed Matter
Replies
1
Views
980
  • Atomic and Condensed Matter
Replies
10
Views
2K
  • Atomic and Condensed Matter
Replies
18
Views
2K
  • Atomic and Condensed Matter
Replies
1
Views
1K
  • Atomic and Condensed Matter
Replies
9
Views
2K
Back
Top