The problem of the Fourier transform of the response to a $\frac{\pi }{2}$ pulse of a single nucleus of spin ½ interacting with a strong rf field is examined theoretically using the density-matrix master equation. In this experiment the nuclear spins are polarized in the rotating frame along a direction different from the laboratory $z$ axis. It is shown that the resulting Fourier-transform spectrum differs in intensities from the steady-state double-resonance spectrum—in contrast with the usual single-resonance case. This phenomenon is understood physically in terms of a rotating-frame model.

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