A highly versatile experiment from the fascinating world of atomic and quantum physics covering the following topics:
 

1. Normal Zeeman Effect
2. Anomalous Zeeman Effect
3. Hyperfine Structure Splitting
4. Fabry-Pérot Interferometer
5. Determination of the Bohr Magneton

 
This experiment investigates the normal and anomalous Zeeman effects using the red (λ = 643.8 nm) and turquoise (λ = 480 nm) cadmium lines. The high-resolution etalon is designed to resolve line shifts of less than 2 pm. Additionally, the hyperfine structure splitting of the turquoise Cd line is clearly visible. The Zeeman effect is studied in both transverse (perpendicular) and longitudinal (parallel) configurations relative to an external, variable magnetic field.
 
Through the theoretical introduction to the Fabry-Pérot etalon, the Bohr magneton can also be experimentally determined in this experiment.
 
Normal Zeeman Effect
The normal Zeeman effect is investigated using the red cadmium line (λ = 643.8 nm). The longitudinal configuration is facilitated by a stepped bore in the pole shoe of the electromagnet. As the light from the Cd lamp passes through the Fabry-Pérot etalon, interference rings are formed, which split into doublets or triplets depending on the direction of the external magnetic field. The linear or circular polarization of the lines is analyzed using a polarization filter and a quarter-wave plate.
The splitting of the interference rings is recorded with a microscope camera. A red filter on the focusing lens enhances the contrast and depth of field for analyzing the Cd lines. The accompanying camera software (for Windows) allows both qualitative observation of the live image and quantitative analysis using screenshots. The experiment is set up on a stable optical precision bench.
 
Anomalous Zeeman Effect
To investigate the anomalous Zeeman effect, the setup for the normal Zeeman effect needs to be modified slightly. The etalon is replaced by a second etalon, and the red filter is substituted with a narrowband bandpass interference filter (FWHM = 10 nm). With this setup, the turquoise cadmium line (λ = 480.0 nm) can be examined. The splitting of the turquoise Cd line in the magnetic field into four (longitudinal) or six (transverse) lines is highly resolved using the Fabry-Pérot etalon. The linear or circular polarization of the lines is analyzed using a polarization filter and a quarter-wave plate.
 
Hyperfine Structure Splitting
In the setup for the anomalous Zeeman effect, the hyperfine structure splitting of the 480 nm cadmium line also becomes visible. In addition to ¹¹⁴Cd (nuclear spin = 0), the Cd lamp contains the isotopes ¹¹¹Cd and ¹¹³Cd, both with a nuclear spin of 1/2. The interaction between nuclear spin and electron leads to hyperfine structure splitting, which in the experiment is visible as up to three additional lines next to the 480 nm line.
 
Fabry-Pérot Interferometer and Determination of the Bohr Magneton
A Fabry-Pérot interferometer is an optical cavity consisting of two plane-parallel mirrors that are partially transparent and have a high reflectivity. The mirrors enclose an optical medium. When the mirrors are at a fixed distance, the setup is also referred to as a Fabry-Pérot etalon. Due to the multiple beam interference, etalons have a very high resolving power.
This part of the experiment is identical to the setup for the normal Zeeman effect. Through the theoretical introduction to the Fabry-Pérot etalon and the investigation of the interference rings, the value of the Bohr magneton can be experimentally determined.