Saturation of the Magnetic Resonance Absorption in Dilute Inhomogeneously Broadened Systems

The existing theory due to Portis for the saturation of inhomogeneously broadened resonances is discussed and a new theoretical formulation of the problem is developmed using an expression for the transition probability first given by Rabi. For $\gamma H_1$ greater than both ${T_1}^{-1\mathrm{}}$ and ${T_2}^{-1\mathrm{}}$, the rf field interacts with spins precessing in the frequency interval $\gamma H_1$; this expression permits explicit calculation of the resulting magnetic loss. No assumption is made of the shape of the individual (homogeneously broadened) spin packets in weak exciting fields. For $F$ centers in alkali halides, the results are identical with those of Portis, but the underlying physical reasons differ.