Echo Sequences

From NMR Wiki

Since the signals in solid state NMR are often very broad, the spins dephase quickly, allowing only a short time for observation. The spectrometers dead time can therefore become a significant problem. To overcome this, a second pulse phased 90° relative to the original excitation, can be used to trigger rephasing of the spins. The time between these two pulses should be equal to the dead time, so that the spins are rephased one aquesition begins.