Photodarkening of Yb-doped aluminosilicate fibers by continuous wave 488 nm irradiation was investigated. The irradiation induced significant excess loss in the UV-visible spectroscopy (VIS) region in Yb-doped aluminosilicate fibers while pure aluminosilicate fibers showed negligible induced loss. Ultraviolet-VIS-near-infrared spectroscopy revealed an absorption peak at 220 nm in unexposed Yb-doped aluminosilicate fiber preforms. The observed peak was attributed to Yb-associated oxygen deficiency centers (ODCs) and proposed as a precursor of the photodarkening. The proposed model was supported by measurements on oxygen-loaded Yb-doped aluminosilicate fibers. In these, the photodarkening could be significantly reduced, which we attribute to a smaller number of ODCs following oxygen loading.

͑͒We describe a technique for surface domain engineering in congruent lithium niobate single crystals. The method is based on conventional electric-field poling, but involves an intentional overpoling step that inverts all the material apart from a thin surface region directly below the patterned photoresist. The surface poled structures show good domain uniformity, and the technique has so far been applied to produce domain periods as small as ϳ1 m. The technique is fully compatible with nonlinear optical integrated devices based on waveguide structures. ͓͔

We report the experimental measurements for etch rates of the zz and 2z faces of single crystal lithium niobate immersed in HF and HNO 3 acid mixtures of varying ratios. We find that pure HF produces an etch rate that is a factor of 2 higher than the rate obtained for the more frequently used mixture of HF/HNO 3 in a 1 : 2 ratio. We further observe that the quality of etching is improved for either pure HF or HF/HNO 3 in a 1 : 4 ratio, again by comparison with use of a 1 : 2 ratio. These results lead to a discussion of the etch chemistry involved, and an explanation for the observed high degree of differential etching between the zz and 2z crystal faces.

Continuous wave ultraviolet laser irradiation at = 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 microstructuring approach when followed by chemical etching. © 2008 American Institute of Physics. ͓DOI: 10.1063/1.2884185͔ Domain engineering 1,2 of lithium niobate ͑LN͒ is a subject of extensive research and a simple, cheap, and robust method of fabrication of well-defined periodic domaininverted structures on submicron scales is highly desirable. Spatial domain engineering is used for many optical processes in bulk crystals and waveguides and can also allow for the creation of both freestanding 3 and surface relief structures 4 through the differential etching characteristics of the polar z faces of the crystal. If achievable on the submicron scale, surface structuring through differential etching will allow the implementation of a range of interesting applications such as tunable photonic crystals, ridge waveguide lasers, and multifunctional micromachines.Previous work has shown that ultraviolet ͑UV͒ and visible laser light can either directly invert 5 or assist the domain inversion process in LN. [6][7][8][9] In this paper, however, a different effect is presented whereby illumination of the +z face with UV light at = 244 nm ͑with photon energy greater than the LN band gap͒ inhibits domain inversion in illuminated areas during subsequent electric field poling ͑EFP͒. Of major importance, the inhibited domains are not restricted in their shape or alignment with the crystal x or y axes, hence, arbitrarily shaped domains can be formed. Some initial results of this effect and its applicability in the creation of micro/nano structures in LN are presented.A beam from a frequency-doubled Ar-ion laser was focused to a spot size of ϳ2.5 m on the +z or −z face of either an undoped congruent or 5 mol % MgO-doped LN crystal. Positioning and exposure control of the crystal was achieved by a computer-controlled, three-axis stage system coupled with a mechanical shutter.For dynamic exposures, sets of parallel lines were drawn on the z faces of the crystals along the crystallographic x or y directions by moving the stages at speeds ranging from 0.05 to 0.3 mm s −1 . For static exposures, arrays of illuminated spots with identical exposure times, ranging from a few milliseconds to a few tens of seconds, were formed. The separation between the edges of adjacent illuminated spots in the arrays varied from 0 to 6 m which permitted us to verify if any proximity effect existed such as that observed in pulsed laser direct poling 5 where the closest approa...

Paper-based microfluidics is a rapidly progressing inter-disciplinary technology driven by the need for low-cost alternatives to conventional point-of-care diagnostic tools. For transport of reagents/analytes, such devices often consist of interconnected hydrophilic fluid-flow channels that are demarcated by hydrophobic barrier walls that extend through the thickness of the paper. Here, we present a laser-based fabrication procedure that uses polymerisation of a photopolymer to produce the required fluidic channels in paper. Experimental results showed that the structures successfully guide the flow of fluids and allow containment of fluids in wells, and hence the technique is suitable for fabrication of paper-based microfluidic devices. The minimum width for the hydrophobic barriers that successfully prevented fluid leakage was ~120 μm and the minimum width for the fluidic channels that can be formed was ~80 μm, the smallest reported so far for paper-based fluidic patterns.