A distributional version of Kirchhoff¿s formula

Kirchhoff?s formula is the equivalent to Green?s Third Theorem for transient waves, representing the solution of the three dimensional wave equation in terms of its boundary data. In this classical result two retarded layer potentials appear. We show in this paper a precise description of these potentials as time convolution with adequate tempered distributions with values on operator spaces. With these potentials in hands we give a self?contained proof of the formula with minimal smoothness requirements.