Photonics Society at UC San Diego
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Zeeman Splitting

Use magnetic fields to change the wavelength of light

The Zeeman effect is quantum mechanical effect where electronic energy levels split slightly in the presence of a magnetic field. The slightness of this effect makes it usually very difficult to observe, but this demo/experiment uses the amazing properties of frequency beating (heterodyne detection) to make this effect visible with relatively modest equipment.

Setup: an unpolarized HeNe tube between permanent magnets, followed by a polarizer and a photodiode with a terminating resistor, connected to an oscilloscope or spectrum analyzer. Below, the optical spectrum shows left- and right-circularly polarized modes separated by a splitting proportional to the magnetic field (typically ~1 MHz); after the polarizer and photodetection, the electrical spectrum shows a single line at that splitting frequency.
Budget
$300–$1000
Required tools
2–3
Manufacturing difficulty
4–5
Alignment difficulty
1–3
Portability
3
Setup time
3–5
Presentation complexity
7–9
Concept complexity
8–9
WOW factor
1–2
What do these scores mean? →
The demo roughly put together on a big optical table in the lab.
A close-up of the beatnote signal measured by the oscilloscope.
Contents01Opportunities for improvement
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Opportunities for improvement

  • Use an electromagnet instead of permanent magnets, so the amount of Zeeman splitting can be varied! This makes the demo substantially more compelling.