Utilizing phases of radio frequency (RF) pulses to manipulate spin dynamics is routine in NMR and MRI, leading to spectacular techniques like phase cycling. In a very different area, cross polarization (CP) also has a long history as part of a vast number of solid-state NMR pulse sequences. However, a detailed study devoted to the effect of CP RF phases on NMR signal, seems not to be readily available. From first principles, we arrive at a simple dependence of NMR signal on arbitrary CP RF phases, for static and MAS conditions, accompanied by experimental verification. In the process, the CP propagator emerges as a product of RF “pulses” and a period of “free precession”, conforming to coherence transfer pathway theory. The theoretical expressions may lend confidence for dealing with CP blocks with tunable phases in pulse sequences.

利用射频 (RF) 脉冲的相位来操纵自旋动力学是 NMR 和 MRI 中的常规操作，这导致了相位循环等壮观的技术。在一个非常不同的领域，交叉极化 (CP) 作为大量固态 NMR 脉冲序列的一部分也有着悠久的历史。然而，关于 CP RF 相位对 NMR 信号影响的详细研究似乎并不容易获得。根据第一原理，我们得出了 NMR 信号对任意 CP RF 相位、静态和 MAS 条件的简单依赖性，并附有实验验证。在此过程中，CP传播子作为RF“脉冲”和“自由进动”周期的产物出现，符合相干传递路径理论。理论表达式可以为处理脉冲序列中具有可调相位的 CP 块提供信心。