## Transition strengths

In zero magnetic field the transition strength may be easily calculated with angular momentum theory and the help of the Wigner–Eckart theorem.

If there is an applied field the transition strengths differ and must be calculated taking the mixing of states into account:

For intermediate fields in the range of a few hundred Milliteslas neither the weak field approximation of the Zeeman regime nor the fully decoupled Paschen-Back regime is a good basis. The full Hamiltonian has to be diagonalized in the eigenbasis.

## Pump Model

The ESR-peak intensities were simulated with a simple pump model of a free Rb atom.

The model predicts the amplitudes of the four ESR lines under different pump laser polarization very well. It also accounts for the pump/probe laser power ratio.

For further spin labeling experiments the ESR peak @ 113.595 mT is the most promising candidate in respect of sensitivity and SNR.

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