Short midinfrared laser pulses efficiently facilitate ultrafast manipulation of ferroic order parameters, including the full reversal of magnetization or ferroelectric polarization, with the invoked mechanisms relating to the properties of polar phonons in ionic crystals. Much less is known, however, about the behavior of such order parameters in response to an excitation in the far-infrared range, where phonons have larger oscillator strengths and are more damped. Here we investigate transient crystallographic strains and polarization switching in ferroelectric barium titanate ($\mathrm{BaTi}{\mathrm{O}}_3$) driven by an excitation in the frequency range of 5–8 THz, or wavelengths of 35–60 µm. We find that switching persists in a large part of this range, but is governed primarily by optical absorption rather than by the longitudinal optical phonons or epsilon-near-zero conditions that dominate in the mid-infrared regime.

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• Ferroelectricity
• Ferroelectrics
• Infrared spectroscopy
• Nonlinear optical techniques
• Optical microscopy
• Optical pumping
• Polarized optical microscopy
• Terahertz sources