The knowledge of terahertz light-matter interaction is rare in the microscopic picture, even though the terahertz light is on the roadmap of various cutting-edge technologies such as 6G communication. We show that terahertz light could strongly interact with the phonon vibration branches via an off-resonant scattering approach, according to thermodynamic theory. Illustrated in group IV monochalcogenide compounds, we present a terahertz-optostrictive deformation process which could effectively tune their geometric structures. Sensitive layer-resolved shift current voltage can be used for detection. Our work has just appeared in PRB as a regular article at https://journals.aps.org/prb/abstract/10.1103/PhysRevB.105.195406.

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