Coherent acoustic perturbation of second-harmonic generation in NiO

Abstract

We investigate the structural and magnetic origins of the unusual ultrafast second-harmonic-generation (SHG) response of femtosecond-laser-excited nickel oxide (NiO) previously attributed to oscillatory reorientation dynamics of the magnetic structure induced by d-d excitations. Using time resolved x-ray diffraction from the ( ) magnetic planes, we show that changes in the magnitude of the magnetic structure factor following ultrafast optical excitation are limited to F m / F m = 1.5% in the first 30 ps. An extended investigation of the ultrafast SHG response reveals a strong dependence on wavelength as well as characteristic echoes, both of which give evidence for an acoustic origin of the dynamics. We therefore propose an alternative mechanism for the SHG response based on perturbations of the nonlinear susceptibility via optically induced strain in a spatially confined medium. In this model, the two observed oscillation periods can be understood as the times required for an acoustic strain wave to traverse one coherence length of the SHG process in either the collinear or anticollinear geometries.

Exchange-Striction Driven Ultrafast Nonthermal Lattice Dynamics in NiO

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Resonant optical control of the structural distortions that drive ultrafast demagnetization inCr2O3

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Ultrafast manipulation of the NiO antiferromagnetic order via sub-gap optical excitation

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