The observation of diffraction spots from strong higher-order combinational gratings during sequential recording of two photorefractive holograms in a LiNbO3 crystal is reported. To the best of our knowledge, this is the first time that combinational photorefractive gratings of third and fourth order have been detected. The influence of the parameters of both intentionally recorded gratings on the amplitude of second-order combinational components (K1+K2 and K1−K2) has been investigated. We have found that the strength of these gratings essentially increases with the amplitude of the first grating recorded and with the modulation of the second grating recorded. However, the combinational gratings behave differently from the second-harmonic gratings in some respects. The results can be qualitatively explained in terms of the nonlinearities of band transport equations.
© 1999 Optical Society of America
E. M. de Miguel-Sanz, J. Limeres, L. Arizmendi, and M. Carrascosa, "Nonlinear generation of higher-order combinational gratings during sequential recording in LiNbO3," J. Opt. Soc. Am. B 16, 1658-1663 (1999)