Media 6: Focus issue introduction: nonlinear optics BoulangerBenoƮt CundiffSteven T. GauthierDaniel J. KarlssonMagnus LuYan-qing NorwoodRobert A. SkryabinDmitry TairaTakunori 2011 Originally published in Optics Express on 07 November 2011 (oe-19-23-23561)