Abstract
The Lau effect consists of generating spatial coherence by using an extended light source that illuminates a double diffraction grating system. The price of this coherence generation is a huge energy loss caused by the successive amplitude gratings, which are blocking elements. To significantly reduce the energy loss, our approach consists in using a longitudinal mirror system to collect the light rays initially blocked by the gratings of the Lau set-up. This technique offers high power efficiency and can be straightforwardly extended to provide Talbot array illuminators. The impact of periodicity error is studied and illustrations are given at the end.