Radiation efficiency of partially coherent electromagnetic beams

Abstract

We present a general definition of the radiation efficiency of stationary electromagnetic fields and prove that it is bounded between zero and unity for beams of any state of coherence and polarization. The radiation efficiency may be interpreted as a measure of how directed the radiated fields are, and therefore it can be used to assess the allowed spatial coherence and intensity variations across a beam. We consider a class of partially coherent electromagnetic fields that were recently introduced in the literature and evaluate the radiation efficiencies for two particular examples, namely, the azimuthally polarized symmetric beams and the dipolar beams that are nearly linearly polarized in the central region. The results show that the radiation efficiency is fairly insensitive to the state of polarization and that it differs appreciably from unity for only small values of source and correlation widths.

Degree of paraxiality for monocromatic beams

“…The importance of the parameter that characterizes paraxiality is obvious because the calculation error itself may be negligible but to estimate reliability of results the level of approximation error must be known and acceptable. Note, then the ratio C is also known as radiation efficiency and has been used to characterize the difference between partially and fully coherent beams [6]. …”