Generation of the second optical harmonic under the action of narrowband terahertz pulses in the antiferromagnet $\rm NiO$

The study examines aspects of the generation of the second optical harmonic in the centrosymmetric antiferromagnet $\rm NiO$ when exposed to narrowband terahertz pulses with an electric field strength on the order of $1$ MV/cm. It was found that when exposed to terahertz pulses with a frequency of $1$ THz, which corresponds to the antiferromagnetic resonance frequency of $\rm NiO$, a significant decrease in the intensity of the second harmonic is observed versus exposure to pulses with a frequency of $1.5$ THz. It is shown that the observed decrease in the intensity of second harmonic generation can be explained by multipath interference during the propagation of a narrowband terahertz pulse in a thin sample.