Magnetization precession after non-collinear dual optical excitation

We investigate the impact of non-collinear dual optical excitation on the magnetization precession in a permalloy thin film using two ultrashort laser pulses. By analyzing the magnetization dynamics using time-resolved magneto-optical methods, we find that the excitation with two ultrashort optical pulses introduces a long-lasting modification of the electron system seen as a sizable decrease of the precession frequency and significant increase (about 25%) of the decay time. Our results reveal that the observed effect strongly depends on the respective polarization of the two excitation pulses and the time delay between two optical pulses. Our findings indicate the occurrence of a new nonlinear opto-spin effect during photoexcitation with two interfering optical pulses which can potentially be observed in various materials and at different photon wavelengths.