Effects of finite pulse width on free induction decay

The shape of the free induction decay for the case in which the amplitude B1 (B1 = omega 1/gamma) of the RF pulse is comparable with local magnetic fields at sites of the nuclei is considered. It is shown that the shape of the FID G(t + tau) (where tau is the width of a RF pulse, t is the time after a RF pulse) depends on the shape of the FID G0(t) following a hard, delta function RF pulse and on the shape of the function F0(tau), which describes the evolution of the longitudinal nuclear magnetization Mz under the effect of the hamiltonian (H0-omega 1 I gamma), where H0 is the interaction hamiltonian of the nuclear spin system. Calculations of F0(tau) and G(t + tau) for different interaction hamiltonians H0 are presented.