All-Optical Domain Inversion in LiNbO Crystals by Visible Continuous-Wave Laser Irradiation.

LiNbO is a distinguished multifunctional material where ferroelectric domain engineering is of paramount importance. This degree of freedom of the spontaneous polarization remarkably enhances the applicability of LiNbO, for instance, in photonics. In this work, we report the first method for all-optical domain inversion of LiNbO crystals using continuous-wave visible light.

Micro-patterns of gold nanoparticles assembled by photovoltaic optoelectronic tweezers: application to plasmonic fluorescence enhancement.

Noble metal nanostructures are well-known for their ability to increase the efficiency of different optical or physical phenomena due to their plasmonic behavior. This work presents a simple strategy to obtain Au plasmonic patterns by optically induced nanoparticle assembly and its application as fluorescence enhancement platforms. This strategy is based on the so-called photovoltaic optoelectronic tweezers (PVOT) being the first time they are used for fabricating Au periodic micro-patterns.

Optoelectronic manipulation of bio-droplets containing cells or macromolecules by active ferroelectric platforms.

Photovoltaic optoelectronic tweezers are a useful platform with many applications in optical manipulation and nanotechnology. They are based on electrical forces associated with the bulk photovoltaic effect presented by certain ferroelectric crystals, such as Fe doped lithium niobate. This manipulation technique has experienced huge developments in recent years, although its use in biology and biomedicine is still scarce.

Time evolution of photovoltaic fields generated by arbitrary light patterns in z-cut LiNbO:Fe: application to optoelectronic nanoparticle manipulation.

The bulk photovoltaic effect is a phenomenon that generates high electric fields in certain ferroelectric crystals under illumination, as iron doped lithium niobate (LiNbO:Fe). A variety of innovative applications of these electric fields require using of z-cut plates, in which the polar axis is normal to the larger crystal faces. However, the kinetics and distribution of the photovoltaic fields in this configuration have not been investigated in depth.

Optoelectronic generation of bio-aqueous femto-droplets based on the bulk photovoltaic effect.

The generation and manipulation of small aqueous droplets is an important issue for nano- and biotechnology, particularly, when using microfluidic devices. The production of very small droplets has been frequently carried out by applying intense local electric fields to the fluid, which requires power supplies and metallic electrodes. This procedure complicates the device and reduces its versatility.

Massive ordering and alignment of cylindrical micro-objects by photovoltaic optoelectronic tweezers.

Optical tools for manipulation and trapping of micro- and nano-objects are a fundamental issue for many applications in nano- and biotechnology. This work reports on the use of one such method, known as photovoltaic optoelectronics tweezers, to orientate and organize cylindrical microcrystals, specifically elongated zeolite L, on the surface of Fe-doped LiNbO crystal plates. Patterns of aligned zeolites have been achieved through the forces and torques generated by the bulk photovoltaic effect.

Optoelectronic tweezers under arbitrary illumination patterns: theoretical simulations and comparison to experiment.

Photovoltaic tweezers are a promising tool to place and move particles on the surface of a photovoltaic material in a controlled way. To exploit this new technique it is necessary to accurately know the electric field created by a specific illumination on the surface of the crystal and above it. This paper describes a numerical algorithm to obtain this electric field generated by several relevant light patterns, and uses them to calculate the dielectrophoretic potential acting over neutral, polarizable particles in the proximity of the crystal.

Photovoltaic versus optical tweezers.

The operation of photovoltaic (PV) tweezers, using the evanescent light-induced PV fields to trap and pattern nano- and micro-meter particles on a LiNbO(3) crystal surface, is discussed. The case of a periodic light pattern is addressed in detail, including the role of particle shape and the modulation index of the light pattern. The use of a single Gaussian light beam is also considered.

Tumour cell death induced by the bulk photovoltaic effect of LiNbO3:Fe under visible light irradiation.

This work reports a pioneer application of the bulk photovoltaic effect in the biomedical field. Massive necrotic cell death was induced in human tumour cell cultures grown on a bulk photovoltaic material (iron-doped lithium niobate, LiNbO(3):Fe) after irradiation with visible light. Lethal doses (≈100% cell death) were obtained with low-intensity visible light sources (10-100 mW cm(-2) irradiances) and short exposure times of the order of minutes.

Fixed holograms in iron-doped lithium niobate: simultaneous self-stabilized recording and compensation.

We analyze the mechanisms leading to a highly diffractive fixed hologram in photorefractive Fe-doped lithium niobate crystals by simultaneous self-stabilized holographic recording and compensation at moderately high temperatures. We show that a partially compensated running hologram is produced during recording under this condition and discuss the performance of the process in terms of the operating temperature, the degree of oxidation ([Fe(3+)]/[Fe(2+)] ratio) of the sample, and the effect of the absorption grating arising from the spatial modulation of the Fe(2+) concentration produced during photorefractive recording. We experimentally measure the evolution of the uncompensated remaining hologram during recording and the evolution of the diffraction efficiency of the fixed hologram during white-light development and show that the maximum fixed grating modulation to be achieved is roughly limited by Fe-dopant saturation.

Holographic phase-shift measurement during development of a fixed grating in lithium niobate crystals.

We report what is believed to be the first direct measurement of the grating phase-shift evolution during white-light illumination for the development of a fixed grating in an Fe-doped lithium niobate crystal. Stabilized holographic recording is shown to be essential for such measurements. Experimental data are in good agreement with theory and allow computation of the relevant material parameters for the sample under analysis.