Ellipsometric investigation of porous silicon layers for the design of a DBR A. Bardaoui, L. Boudaya, T. Abdellaoui, N. Ben Sédrine, M. Lajnef and R. Chtourou Eur. Phys. J. Appl. Phys., 43 1 (2008) 87-91 Published online: 19 June 2008 DOI: 10.1051/epjap:2008126