Optical Pumping (Zeeman Effect)

[ssj2poliwhirl]

I am a bit confused about optical pumping-style experiments, and why increasing the strength of the magnetic field increases the amount of optical pumping --> increases the transmission of light through rubidium

So basically we have Rubidium with energy levels like this:
http://t3.gstatic.com/images?q=tbn:ANd9GcRPcNj_MWyOh1pOkvsfohSY6o9HRxO25v031mNC2xG7nFfnoWtj2Q

My understanding is, an external magnetic field will cause the final splittings on the right (into m_F levels), and as we increase the magnetic field from 0 the gap between the m_F levels gets broader [until we pass the weak field limit and get the quadratic Zeeman effect instead].

Can someone help me understand why increasing this gap increases the amount of pumping/rubidium polarization we get? Based on the theory of how/why it work, it just seems like, 'as long as there is a gap, we will get optical pumping'. Why does an applied field cause so much more light transmission than just the Earth's magnetic field?

 

[eljose79]

Great question! Let me explain the concept of optical pumping and how increasing the magnetic field can enhance it.

Optical pumping is a process in which atoms are excited from a lower energy state to a higher energy state through the absorption of light. This is typically done using a laser, which emits light at a specific frequency that corresponds to the energy difference between the two states.

In the case of rubidium, the atoms have multiple energy levels, as shown in the diagram you provided. When a laser is shined on the atoms, it can excite them from the ground state (F=2) to the excited state (F=3). However, due to the presence of the external magnetic field, the energy levels split further into mF levels. This means that there are multiple paths for the atoms to be excited, depending on the orientation of the magnetic field.

Now, here's where the increasing magnetic field comes into play. When the magnetic field is weak, the energy gap between the mF levels is small, and the atoms can easily jump between the different levels. This results in a lower degree of polarization, as the atoms are not all in the same energy level.

However, when the magnetic field is increased, the energy gap between the mF levels also increases. This means that the atoms can only be excited to specific mF levels, and it becomes more difficult for them to jump to other levels. As a result, more atoms end up in the same energy level, leading to a higher degree of polarization.

So, to answer your question, increasing the magnetic field increases the energy gap between the mF levels, making it more difficult for the atoms to jump between levels. This results in a higher degree of polarization and an increase in the amount of light transmitted through the rubidium sample.

As for why the Earth's magnetic field is not sufficient for this effect, it is simply because the field is not strong enough. The Earth's magnetic field is relatively weak compared to the field used in optical pumping experiments, and therefore the energy gap between the mF levels is not significant enough to cause a noticeable increase in polarization.

I hope this helps to clarify the concept of optical pumping and the role of the magnetic field in enhancing it. Let me know if you have any further questions. Happy experimenting!