# NMR rotating frame

I'm reading about a linearly polarized field (in the context of NMR). The field is given by

$${\bf H_{lin}}=2H_1({\bf i}cos(\omega_zt)).$$

This can be created by having a pulse field plus its mirror image; i.e.

$${\bf H_1}=H_1({\bf i}cos(\omega_zt)+{\bf j}sin(\omega_zt)).$$

The mirror image field in the lab frame is obviously the same as ${\bf H_1}$ expect $\omega_z \rightarrow -\omega_z.$

Now, my question is what is the expression for the counter-rotating "mirror image" field in the ROTATING frame? I've having some trouble working through this...

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