= Scalar wave intensity
{title2=$I=|E|^2$}
For a scalar complex <wave amplitude> $E$, the squared-amplitude <scalar wave intensity> convention is $I=EE^*$. It is nonnegative and unchanged by multiplying $E$ by a unit-modulus <wave phase> factor. This convention is useful in <paraxial propagation> and <phase screen> models. Conversion to physical <energy flux> also depends on the field variable and medium; an arbitrary superposition need not have its full flux determined by this scalar alone. For a random field, $\langle I\rangle$ is the <mean wave intensity>, whereas $|\langle E\rangle|^2$ is the squared <coherent field>; these generally differ.
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