Rotational Echo DOuble Resonance (REDOR) experiment,  are a type of heteronuclear dipolar recoupling experiment which enable one to re-introduce heteronuclear dipolar couplings averaged by MAS.  The reintroduction of such dipolar coupling reduce the intensity of the NMR signal intensity compared to a reference spectrum where no dephasing pulse is used.  REDOR can be used to measure heteronuclear distances, and are the basis of NMR crystallographic studies.