A.C. Muir

Precision nanoscale domain engineering of lithium niobate via UV laser induced inhibition of poling

Continuous wave ultraviolet (UV) laser irradiation at lambda=244 nm on the +z face of undoped and MgO doped congruent lithium niobate single crystals has been observed to inhibit ferroelectric domain inversion. The inhibition occurs directly beneath the illuminated regions, in a depth greater than 100 nm during subsequent electric field poling of the crystal. Domain inhibition was confirmed by both differential domain etching and piezoresponse force microscopy. This effect allows the formation of arbitrarily shaped domains in lithium niobate and forms the basis of a high spatial resolution micro-structuring approach when followed by chemical etching.

Direct-writing of inverted domains in lithium niobate using a continuous wave ultra violet laser

The inversion of ferroelectric domains in lithium niobate by a scanning focused ultra-violet laser beam (lambda = 244 nm) is demonstrated. The resulting domain patterns are interrogated using piezoresponse force microscopy and by chemical etching in hydrofluoric acid. Direct ultra-violet laser poling was observed in un-doped congruent, iron doped congruent and titanium in-diffused congruent lithium niobate single crystals. A model is proposed to explain the mechanism of domain inversion.

Design and performance of a ZnSe tetra-prism for homogeneous substrate heating using a CO2 laser for pulsed laser deposition experiments.

We report on the design and performance of a ZnSe tetra-prism for homogeneous substrate heating using a continuous wave CO(2) laser beam in pulsed laser deposition experiments. We discuss here three potential designs for homogenizing prisms and use ray-tracing modeling to compare their operation to an alternative square-tapered beam-pipe design. A square-pyramidal tetra-prism design was found to be optimal and was subjected to modeling and experimental testing to determine the influence of interference and diffraction effects on the homogeneity of the resultant intensity profile produced at the substrate surface. A heat diffusion model has been used to compare the temperature distributions produced when using various different source intensity profiles. The modeling work has revealed the importance of substrate thickness as a thermal diffuser in producing a resultant homogeneous substrate temperature distribution.

Ultraviolet laser-induced submicron spatially resolved superhydrophilicity on single crystal lithium niobate surfaces

Lithium niobate crystal surfaces become super-hydrophilic after ultraviolet laser irradiation. The crystal surface hydrophilicity, which was assessed by the contact angle of a sessile drop of de-ionised water, was found to undergo a transition from mildly hydrophobic (contact angle, theta[E] < 50°) to a super-hydrophilic state ( theta[E] < 5° ). Patterning of the hydrophilicity at the micron and sub-micron range has been achieved by spatially modulating the illuminating laser beam.

UV laser radiation inhibits domain inversion in lithium niobate

Continuous wave UV laser (lambda = 244 nm) irradiation of the +z face of lithium niobate single crystals inhibits ferroelectric domain inversion in the volume of the crystal which lies immediately below the UV exposed surface.

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).

Modelling of UV direct-write waveguides in single crystal lithium niobate

It has been shown that waveguide structures can be directly written into single crystal LiNbO/sub 3/ through the influence of a focussed c.w. laser source at a wavelength of 244 nm scanned across the surface.

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.