A WAVE THEORY FOR NONIMAGING CONCENTRATORS

An expression is found for the propagation of the radiance function fo r light in any state of coherence through a concentrator which can be represented by a linear, stationary optical system. For light from a q uasi-homogeneous source this expression can be somewhat simplified by an approximation. It is shown that the radiance function is invariant for a large class of optical systems. Finally it is shown that fundame ntal limitations for the concentration of light follow from the uncert ainty principle and the second law of thermodynamics, which apply quit e generally. These relations show why quasi-homogeneous light (i.e. li ght from thermal sources) cannot be concentrated as well as light from some other sources (such as light from a laser).