Characterization and dynamics of gratings induced in glasses by femtosecond pulses

We characterize the gratings induced in commercial SF57 glass by femtosecond pulses. A simple technique enables us to measure both the real and the imaginary parts of the refractive index and shows that the induced grating is mainly a phase grating. An index variation of as much as 6 x 10(-3) is reported. Then we study the diffraction efficiency of the grating with respect to the intensity of the femtosecond pulse. Permanent structures are induced above the damage threshold. Below this threshold, the grating relaxes. The long-time dynamics of the decay is studied and described by two models. The formation of transient and permanent gratings in various other glasses is observed. (C) 2002 Optical Society of America.