Optical second harmonic generation induced by picosecond terahertz pulses in centrosymmetric antiferromagnet NiO

Optical second harmonic generation at the photon energy of $2\hbar\omega=2$ eV in the model centrosymmetric antiferromagnet NiO irradiated with picosecond terahertz pulses ($0.4$–$2.5$ THz) at room temperature is detected. The analysis of experimental results shows that induced optical second harmonic generation at the moment of the impact of a terahertz pulse arises through the electric dipole mechanism of the interaction of the electric field of a pump pulse with the electron subsystem of NiO. Temporal changes in optical second harmonic generation during $7$ ps after the action of the pulse are also of an electric dipole origin and are determined by the effects of propagation of the terahertz pulse in a NiO platelet. Coherent oscillations of spins at the antiferromagnetic resonance frequency induced by the magnetic component of the terahertz pulse induce a relatively weak modulation of magnetic dipole optical second harmonic generation.