We report the first experimental observation of 3D-LBs, excited by
femtosecond pulses in a system featuring quasi-instantaneous cubic nonlinearity
and a periodic, transversally-modulated refractive index. Stringent evidence of
the excitation of LBs is based on time-gated images and spectra which perfectly
match our numerical simulations. Furthermore, we reveal a novel evolution
mechanism forcing the LBs to follow varying dispersion/diffraction conditions,
until they leave their existence range and decay.Comment: 4 pages, 5 figures - Published by the American Physical Societ