Influence of laser pulse shaping on the ultrafast dynamics in antiferromagnetic NiO

Femtosecond laser excitation of antiferromagnetic NiO leads to an oscillatory temporal behavior of optical second-harmonic generation in this material. Depending on laser pulse length, these oscillations have frequencies of either 55 or 1 GHz, which correspond to the magnetic anisotropy energy separating the ground state with spins along the < 11 (2) over bar > axis from the excited states with spins along the < 111 > or < 1 (1) over bar0 > axis, respectively. The oscillations can be explained as beatings between the ground and the respective excited state triggered by an instantaneous laser-induced flip of the Ni2+ spins which can thus be controlled three dimensionally by pulse shaping.