Optical tuning of dielectric properties of SrTiO3:Fe in the terahertz range

Tuning of the dielectric permittivity spectra of iron-doped strontium titanate (SrTiO3:Fe) single crystals in an external optical field is investigated at room temperature by means of terahertz time-domain spectroscopy. Application of the optical field leads to an appreciable tuning of the permittivity, which reaches up to 3.8%. The observed behavior is interpreted in terms of soft-mode hardening due to the anharmonic character of its potential. We also find that the change of refractive index has a linear relationship on scale with the applied light power. These findings are attributed to the internal space charge field of photorefraction caused by the excited free carriers. (C) 2013 Optical Society of America