Photo-induced ferroelectric order evidenced by picosecond X-ray difraction M.H. Lemée-Cailleau, E. Collet, M. Buron, H. Cailleau, M. Wulff et S. Techert J. Phys. IV France, 12 9 (2002) 183 DOI: 10.1051/jp4:20020391