}\int {{\bf \tilde E}\left( {\bf k} \right)e^{i{\bf k} \cdot {\bf r}-i\omega({\bf k})t} } d^3 {\bf k}~,$$ where $d^3{\bf k}=dk_x dk_y dk_z = k^2\sin\theta dk d\theta d\phi$, $\omega({\bf k})=k$ is the dispersion relation, factor $g=\sqrt{2\omega/\varepsilon_0}$ ($\varepsilon_0$ is the vacuum permittivity) is introduced for proper normalization of energy below, and the real wave electric field is given by ${\bm {\mathcal E}}\left( {\bf r},t \right) = {\rm Re}\, {\bf E}\left( {\bf r},t \right)$. In the helicity basis one has $$\label{eqn:A2}
{\bf \tilde E}\left( {\bf k} \right) = \tilde E^{+} \left( {\bf k} \right){\bf e}^{+} \left( {\bf k} \right) +
\tilde E^{-} \left( {\bf k} \right){\bf e}^{-} \left( {\bf k} \right)~.$$ The energy of the wave-packet field is given by the 3D space integral of the intensity (we omit inessential constant factors) and can be written as: $$\begin{aligned}
\label{eqn:A3}
\nonumber
W = \frac{1}{2}\int {\left(\varepsilon_0{\left| \bm{\mathcal E} \right|}^2+ \mu_0{\left| \bm{\mathcal H} \right|}^2\right)} {d^3}{\mathbf{r}} \\
\nonumber
= \frac{1}{4}\int {\left(\varepsilon_0{{\left| \bf{E} \right|}^2}+ \mu_0{{\left| \bf{H} \right|}^2}\right)} {d^3}{\mathbf{r}} \\
= \int {\omega{{\tilde E}^{\sigma *}}{{\tilde E}^\sigma }{d^3}{\mathbf{k}}}  \equiv \left\langle {{{\tilde E}^\sigma }} \right|\omega \left| {{{\tilde E}^\sigma }} \right\rangle.\end{aligned}$$ Here ${\bm {\mathcal H}}\left( {\bf r},t \right) = {\rm Re}\, {\bf H}\left( {\bf r},t \right)$ is the magnetic field, $\mu_0$ is the 