New formulation of the quantummechanical analogue of the wiener-khintchine theorem for electromagnetic fields

A new formulation of the quantum-mechanical analogue of the Wiener-Khintchine theorem is presented. It is shown that for the radiation fields with null unpaired second-order correlation tensors and with the modes arbitrarily correlated, the trace of the paired secondorder correlation tensor between two arbitrary timest1 andt2 at the space pointr and the spectral energy density at the space-time point [r, (t 1 + t 2 )/2] form a Fourier-transform pair. The condition of crossspectral purity is briefly discussed for fields obeying the new formulation of the Wiener-Khintchine theorem.