Picosecond light-induced noncentrosymmetry in a dye solution

By means of a phase-conjugation experiment by nondegenerate six-wave mixing, we demonstrate a transient ${\mathrm{\chi }}^{\mathrm{}\left(2\right)\mathrm{}}$ grating induced by a nonzero ${\mathit{E}}^3$ time average in a solution of noncentrosymmetric dye molecules. The origin of the induced phase-matched second-harmonic generation is found in an orientational hole-burning effect. Its lifetime, limited by molecule rotation, is 210±10 psec and the ${\mathrm{\chi }}^{\mathrm{}\left(2\right)\mathrm{}}$ magnitude reaches 2.5×${10}^{\mathrm{-}3}$ pm/V for 1 GW ${\mathrm{cm}}^{\mathrm{-}2}$ pumps at 1064 nm.