Light-induced Domain Research Articles

Light-Assisted Generation of Tailored Ferroelectric Domain Structures

Two different methods for light-induced domain inversion in lithium niobate crystals are currently under investigation. Illumination with ultra-violet light with photon energies smaller than the band gap (wavelength λ = 334 nm) can reduce the coercive field by 50% in crystals doped with more than 5 mol% magnesium. In near-stoichiometric crystals doped with iron, space-charge fields can be imprinted by inhomogeneous illumination with visible light (λ = 488 nm). Biased with an external electric field this leads to tailored domain inversion. The high electric fields at the head-to-head domain boundaries are compensated by the space-charge field.

Impact of ultraviolet light on coercive field, poling dynamics and poling quality of various lithium niobate crystals from different sources

Ferroelectric domain reversal by electric field poling of lithium niobate crystals (LiNbO3) with varying stoichiometry and magnesium (MgO) doping level obtained from various commercial suppliers is investigated. Magnesium doping lowers the domain-wall velocity, increases the uniformity of the growth of the domains, and reduces the impact of crystal symmetry on the shape of the domains. Illumination with ultraviolet (UV) laser light (305nm) reduces the coercive field by up to 34% in MgO-doped crystals, but is accompanied by a degradation of poling quality. UV light of longer wavelengths (334nm) has no influence on the coercive field except for the MgO:LiNbO3 material of one supplier, where the field is reduced by 27%. In this case the poling quality is excellent. UV-induced reduction of stress-induced birefringence is observed in some samples. The results are of crucial relevance for light-induced domain engineering of LiNbO3 crystals.

The photorefractive effect for neutron and synchrotron radiation

Electro-optic and photorefractive effects for neutrons and X-rays are discussed. Unclamped neutron electro-optic constants are typically some fm/V. The clamped neutron electro-optic coefficient is about four orders of magnitude smaller and depends on the neutron spin. Other photorefractive mechanisms for particle radiation are the chemo-optic effect, light-induced ionic charge transport and light-induced domain switching.