C.E. Valdivia

Nanoscale surface domain formation on the +z face of lithium niobate by pulsed ultraviolet laser illumination

Single-crystal congruent lithium niobate samples have been illuminated on the +z crystal face by pulsed ultraviolet laser wavelengths below (248 nm) and around (298-329 nm) the absorption edge. Following exposure, etching with hydrofluoric acid reveals highly regular precise domain-like features of widths ~150-300 nm, exhibiting distinct three-fold symmetry. Examination of illuminated unetched areas by scanning force microscopy shows a corresponding contrast in piezoelectric response. These observations indicate the formation of nanoscale ferroelectric surface domains, whose depth has been measured via focused ion beam milling to be ~2 micron. We envisage this direct optical poling technique as a viable route to precision domain-engineered structures for waveguide and other surface applications.

Light-induced order-of-magnitude decrease in the electric field for domain nucleation in MgO-doped lithium niobate crystals

We report an order-of-magnitude reduction in the electric field required for domain nucleation in 1 mol % MgO-doped near-stoichiometric and 5 mol % MgO-doped congruently grown lithium niobate crystals induced by illumination from a focused continuous wave laser beam at wavelengths of 514, 488, and 457 nm. A smaller decrease of 31% is also observed for undoped congruently grown crystals. The effect is independent of the visible wavelengths explored. Light-controlled domain patterning is also demonstrated.

Colloidal photonic crystal cladded optical fibers: Towards a new type of photonic band gap fiber

A facile approach of fabricating a new type of hollow photonic band gap fibers is proposed. Templates for generating such fibers are demonstrated by a complete and uniform coating of a standard silica optical fiber (125 mum diameter) with a three-dimensional colloidal photonic crystal through isothermal heating evaporation induced self-assembly. The photonic crystal cylindrical annulus is characterized by optical and scanning electron microscopy, and is found to yield a 1.4-mum stop band by optical reflection and transmission spectroscopy. The results also demonstrate a practical means of enveloping macro- or micro-curved surfaces with three-dimensional photonic crystals, a task that is geometrically challenging by other photonic crystal fabrication methods.

Ultrashort-pulse optically-assisted domain engineering in lithium niobate

Ultrashort laser pulses (∼120–150 fs) of near-ultraviolet (305 nm) to near-infrared (800 nm) wavelengths have been used to optically-assist domain nucleation and growth in lithium niobate. Within illuminated areas, the electric field required for domain nucleation is reduced by up to 41% in undoped and up to 98% in 5-mol% Mg-doped congruently melting materials, allowing direct-writing of inverted domains with electric fields as small as 100 V mm− 1. A first step towards the formation of optically-defined periodically poled lithium niobate was achieved by illumination via a phase mask, demonstrated over small areas with a period of 5.25 microns.

Latent light-assisted poling of LiNbO3

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.

Ultrashort-pulse light-assisted periodic poling of lithium niobate and lithium tantalate

We report the light-assisted poling of controllable periodic and arbitrarily-shaped domain patterns in lithium niobate and lithium tantalate via the simultaneous application of a low uniform DC electric-field and sequence of ultrashort pulses (150-200 fs).

Visible-light-induced tenfold reduction of the electric field required for ferroelectric domain nucleation in MgO-doped lithium niobate

An order of magnitude reduction in the electric field required for ferroelectric domain nucleation is observed in MgO-doped lithium niobate crystals using focused visible light from an Ar-ion laser

UV laser-induced ferroelectric domain structures investigated by piezoresponse force microscopy

Ferroelectric domains have been generated on the +z and the -z faces of congruent undoped lithium niobate (LiNbO3) single crystals by direct UV writing using a continuous wave (c.w.) frequency doubled argon ion laser (lambda=244 nm). The width of the domains was observed to depend on the intensity of the laser beam. Interestingly, also the contrast of the domains seen by piezoresponse force microscopy (PFM) was observed to increase with higher laser intensity. The contrast difference could be attributed to a difference of the depth of these surface domains as the depth sensitivity of the PFM is ~1 mum for LiNbO3.

Latent ultrafast laser-assisted domain inversion in congruent lithium niobate

A full study of the latent coercive field modification and domain expansion dynamics is reported in the paper. In this investigation a transparent cell was used for the illumination and poling of the crystals which allowed in situ observation of the domain formation (via stress-induced birefringence and electro-optic refractive index contrast at the inverted domain boundaries).

UV radiation-induced surface wetting changes in lithium niobate single crystals

Irradiation of lithium niobate crystal surfaces with UV radiation modifies the wetting properties of the surface which becomes super-hydrophilic. This effect is used for spatially selective attachment of chemical species on the laser exposed areas.