Is electromagnetic wave intensity always the norm of the Poynting vector?

[kent davidge]

Is the intensity of a general electromagnetic wave always the norm of its Poyinting vector?
Or are there other notions of intensity?

 

[vanhees71]

Since by definition "intensity" is the energy flux per unit time that's right, but usually you have to take also the temporal average. Also see

https://de.wikipedia.org/wiki/Intensität_(Physik)

Note that the energy flux for an em. field (in vacuo) is given by the Poynting vector
$$\vec{I}=\vec{S}=\frac{1}{\mu_0} \vec{E} \times \vec{B}.$$