A Wave Theory for Non-Imaging Concentrators

An expression is derived for propagation of the radiance function for light in any state of coherence through a concentrator that can be represented by a linear, stationary optical system. For light from a quasi-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. It is also shown that fundamental limitations for the concentration of light follow from the uncertainty principle and the second law of thermodynamics, which apply quite generally. These relations show why quasi-homogeneous light such as light from thermal sources can not be concentrated as well as light from some other sources such as light from a laser.