Femtosecond index grating in barium flouride: efficient self-diffraction and enhancement of surface SHG

A transient refractive index grating is formed in barium fluoride crystals under irradiation with femtosecond laser pulses from two non-collinear beam s. At low intensities energy coupling takes place. At high intensities, a t ypical self-diffraction pattern is obtained with a diffraction efficiency b etter than 10%. Simultaneously, an enhancement of the SHG signal from the s urface, as well as the generation and diffraction of the third harmonic is observable. For all effects the nonlinear Kerr-effect is responsible, with the response time being limited only by the temporal pulse shape. (C) 2000 Elsevier Science B.V. All rights reserved.