Radiation gauge
= Radiation gauge
{title2=$A_0=0,\quad\partial_iA_i=0$}
For a free <electromagnetic field> with suitable boundary conditions, combine <Coulomb gauge> $\partial_iA_i=0$ with $A_0=0$. <Gauss's law> makes the second condition consistent in the source-free problem. The remaining field operator is spatially transverse and describes the two radiative <photon> polarizations. A constrained scalar potential must be restored when charges are present.