Schematic presentation of the effect of phase cycling
By a systematic variation of either the pulse phase (left) or the receiver/observe phase we can supress undesired magnetization.
Left: The phase of a p/2- pulse is shifted in increments of 90 º while keeping the receiver phase constant. The phase of the resulting signal in a one-pulse experiment changes in conjunction with the phase change of the pulse. Coaddition of the four resonance signals leads to complete signal cancellation .
Right:The same effect can be observed by a systematic Receiver phase change. Again, a systematic 90 phase shift , this time of the receiver while leaving the pulse phase constant, results in cancellation.
As coherence responds differently to phase changes (depending on coherence order, and position) this can be used to select/supress specific coherences.