Variable period change of femtosecond written fiber Bragg gratings with a deformed wavefrontChristian Voigtländer, Ria G. Krämer, Jens U. Thomas, Daniel Richter, Andreas Tännermann and Stefan NolteMATEC Web of Conferences, 8 (2013) 06013DOI: https://doi.org/10.1051/matecconf/20130806013