Electric field sensing (electrometry) using the AC Stark effect or Autler–Townes effect


Splitting/spacing of spectral lines proportional to electric field amplitude
Atomic spectroscopy and Electromagnetically Induced Transparency (EIT)
Electric field sensing - Applications in areas of "weather, electronic devices, environmental and astronomical science."
How do you detect electromagnetic waves e.g. those emanated from a device? Specifically how do you detect the electric component (field) of an electromagnetic wave or the electric field distribution of a device?
Using an antenna e.g. dipoles and loop antennas.
It is believed that using an antenna "limits the precision at which the electric field distribution can be determined."
Haoquan F. et al 2015 J. Phys. B: At. Mol. Opt. Phys. 48 202001
The alternative is atomic spectroscopy electrometry, an "atomic antenna".
The example of radiofrequency electrometry using laser (infrared) spectroscopy and atomic transitions of Rydberg atoms
AC Stark effect or Autler–Townes effect
Based on the principle of Electromagnetic Induced Transparency (EIT)
Splitting/spacing of spectral lines proportional to electric field amplitude
[Figure 3 - lowest panel] If we consider a glass cell with Cesium atoms upon which we shine a laser tuned at the D2 transition of Cesium i.e. 852 nm, then the electrons found on the ground state (6S) will absorb the light (electromagnetic) energy and will transition to a higher energetic state (6P).
As the atoms will absorb all the light that is shined upon them, there will no light coming out of the cell. The cell will appear opaque to light as there will be full absorbance. (This would be the opposite of transparency).
The absorbance curve is demonstrated in the lowest right-hand panel of Figure 3 (the transmission represented on the y axis tends to become zero).
Electrons may decay to the ground state. As long as the ground state is populated by electrons, which can absorb light and transition to a higher energetic state, the absorbance will be sustained.
[Figure 3 - middle panel] If we simultaneously shine on the glass cell another laser tuned at 509 nm, this will mediate a transition of electrons from the previous excited state (6P) to the nD state. (We have coupled a new transition to the previous one. Also this laser light is termed "coupled laser" or "control laser").
If all electrons move to the new excited state, it is possible that there will be no electrons decaying to the 6S ground state.
In the absence of electrons on the ground state, it will no longer be possible to absorb laser light of 852 nm as there are no electrons to absorb it.
Due to this, 852 nm light will be transmitted in the cell (light will go through the cell) and will not be absorbed. In other words, the cell will become transparent to 852 nm light. Electromagnetically Induced Transparency will take place.
This is demonstrated in the middle right-hand side panel where a peak of transmission appears.
[Figure 3 - highest panel] If an electric field is resonant with another transition as shown at the highest panel, it can induce a narrow absorption feature or in other words it can split the transmission lineshape in two peaks.
The splitting between the transmission peaks is proportional to the electric field amplitude as shown in Figure 2.














Laser 1 induces absorbance by an atom population due to a certain transition.
Laser 2 mediates another transition that couples to the previous one and cancels it (interferes with it) thereby inducing a window of transparency (non-absorbance).
Radiofrequency field couples to laser 2 transition illustrating the notion of the atomic antenna: an atomic population illuminated by laser light which "flickers in time to any ambient radio waves. They call it atomic radio."
“The atomic radio wave receiver operates by direct real-time optical detection of the atomic response to AM and FM baseband signals, precluding the need for traditional de-modulation and signal-conditioning electronics,”
“We demonstrate an atom-based receiver for AM and FM microwave communication”
Paper: "An atomic receiver for AM and FM radio communication"