Pump-probe study of E(TO) polaritons in Zn-doped LiNbO3

Results of femtosecond pump-probe measurement of E(TO)-like polaritons in Zn-doped lithium niobate crystals are presented. The impulsive-stimulated-Raman-induced three delay-time oscillations, omega(1), omega(2) and omega(3), are found and assigned to the linear combinations of three lowest E(TO)-like polaritons, nu(1), nu(2), and nu(3), which are omega(1) = nu(2) - nu(1), omega(2) = nu(3) - nu(1) and omega(3) = 2nu(1). The obtained frequencies of omega(1), omega(2) and omega(3) are well explained by dielectric dispersion calculation. The lifetimes of these oscillations induced by the electro optical effect are also deduced, and they are strongly correlated with the Raman lineshape of E(TO) phonons. Our results also imply that the vibrations of E(TO1) and E(TO2) are mainly attributed to the Nb and O atomic motions, while the vibration of E(TO3) is dominated by the defect structure.