Far-infrared dispersion of complex dielectric constant in the ferroelectric near-stoichiometric LiNbO3:Fe

The dielectric properties of near-stoichiometric LiNbO3:Fe single crystal have been investigated by using a terahertz time domain spectroscopy (THz–TDS) in a frequency range of 0.7–1.6 THz at room temperature. When coupled with an applied external optical field, an obvious photorefractive effect was observed, resulting in the modulation of the complex dielectric constant for near-SLN:Fe. The variation of refractive index |Δn| has a linear relationship on scale with the applied light intensity accompanied with a steplike decrease. These findings were attributed to the internal space charge field of photorefraction and the light-induced domain reversal in the crystal.

► We report the THz spectroscopy of near-stoichiometric LN:Fe single crystal.
► An obvious photorefractive effect was observed accompanied with a steplike decrease of photorefraction in the crystal.
► The photorefraction of near-SLN:Fe was supposed to originate from the internal space charge field caused by free carriers.
► The light-induced domain reversal in the crystal leads to a steplike decrease of photorefraction.