Abstract
The observation of latent light-assisted poling (LAP) in lithium niobate single crystals is reported. More specifically, the nucleation field is reduced and remains reduced for an extended time period (up to several hours) after irradiation with ultrafast (approximately 150 fs) laser light at a wavelength of 400 nm. The maximum nucleation field reduction measured using latent-LAP (62%) was significantly higher in comparison with regular non-time-delayed LAP (41%) under identical irradiation conditions in undoped congruent lithium niobate crystals. No latent-LAP effect was observed in MgO-doped crystals for the experimental conditions used, despite the strong effect observed using regular LAP. The latent-LAP effect is attributed to the formation of a slowly decaying photo-induced space-charge distribution which assists local ferroelectric domain nucleation. The dynamics of latent-LAP are compared with the dynamics of photorefractive grating decay, recorded in lithium niobate crystals of different doping, confirming the space charge hypothesis.
Highlights
Single crystal lithium niobate (LN) is a ferroelectric crystal, which exhibits a spontaneous electric polarization along its z-axis, the direction of which can be inverted by the application of an external electric field (E-field)
Recent research investigating the influence of light on electric field poling (EFP) revealed that illuminated regions require a lower nucleation field, En in both undoped congruent LN (CLN) and MgO-doped CLN (MgO)-doped LN using c.w. [7,8,9,10,11,12] and pulsed laser light [13] in a process referred to as light-assisted poling (LAP)
latent light-assisted poling (LLAP) enables the de-coupling of the light illumination and application of the externally Efield, and has been demonstrated in undoped CLN
Summary
Single crystal lithium niobate (LN) is a ferroelectric crystal, which exhibits a spontaneous electric polarization along its z-axis, the direction of which can be inverted by the application of an external electric field (E-field). In this paper we show that in undoped CLN, the En reduction can be observed even several hours after light illumination Using this technique, called latent light-assisted poling (LLAP), the two processes of light illumination and application of an external E-field can be de-coupled. The presence of a photo-induced space-charge distribution and the corresponding space-charge field induces a refractive index change in LN via the electro-optic effect Probing of this photorefractive index change provides an excellent tool for the investigation of the LLAP dynamics. The domain nucleation for varying time-delays between light illumination and application of the external E-field in undoped CLN is investigated, while in Section 3 the LLAP dynamics are compared to the decay of a photorefractive grating formed by the space-charge field The domain nucleation for varying time-delays between light illumination and application of the external E-field in undoped CLN is investigated in Section 2, while in Section 3 the LLAP dynamics are compared to the decay of a photorefractive grating formed by the space-charge field
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