Microwave radiation is applied to a sample in a tunable magnetic field. This field is scanned across a certain range, yielding the resonance peaks that can be used to determine the components of the g-factor. The magnetic field is then rotated slightly and the new components of the g-factor are determined. Putting this data together allows the figures above to be produced.
“The deviation of the measured g-factor from that of the free electron arises from spin-orbit coupling between the ground state and excited states.”
How do the ground state and excited states interact through spin-orbit coupling?