Radiation Efficiency of Partially Coherent Planar Sources with Various Intensity Distributions

Abstract

A general expression is derived for radiation efficiency, which is defined as a ratio of the radiated energy flux to the source-integrated intensity, of partially coherent planar sources with arbitrary intensity distributions. On the basis of the expression, radiation efficiencies of the sources with various intensity distributions are quantitatively investigated as a function of both the coherence condition and the intensity distribution across the source. By stemming from the present source model whose spatial coherence is characterized by Bessel functions, a physical origin of the variation in radiation efficiency is satisfactorily presented in connection with the spatial frequency spectrum of the source associated with evanescent waves. As a result, it is found that the broad spread in spatial frequency spectrum of the source results in the reduction of radiation efficiency for the sources with arbitrary intensity distributions including the quasi-homogeneous ones and that the behaviour of this kind is independent of the presence of evanescent waves, at least, for the quasi-homogeneous sources.