Ceramic welding methods and welded articles are disclosed. The present disclosure shows that transparent and diffuse ceramics can be successfully joined using lasers. The diffuse ceramic welding can be aided by introducing a small gap for optical penetration while no gap is necessary in the transparent ceramics case. Laser welding is more versatile on transparent ceramics since one can focus through the material allowing the joining of more complex geometries and over multiple interaction zones, increasing the ultimate weld volumes.

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Ultrafast laser welding of ceramics

Traditionally accepted design paradigms dictate that only optically isotropic (cubic) crystal structures with high equilibrium solubilities of optically active ions are suitable for polycrystalline laser gain media. The restriction of symmetry is due to light scattering caused by randomly oriented anisotropic crystals, whereas the solubility problem arises from the need for sufficient active dopants in the media. These criteria limit material choices and exclude materials that have superior thermo-mechanical properties than state-of-the-art laser materials. Alumina (Al2O3) is an ideal example; it has a higher fracture strength and thermal conductivity than today’s gain materials, which could lead to revolutionary laser performance. However, alumina has uniaxial optical proprieties, and the solubility of rare earths (REs) is two-to-three orders of magnitude lower than the dopant concentrations in typical RE-based gain media. We present new strategies to overcome these obstacles and demonstrate gain in a RE-doped alumina (Nd:Al2O3) for the first time. The key insight relies on tailoring the crystallite size to other important length scales—the wavelength of light and interatomic dopant distances, which minimize optical losses and allow successful Nd doping. The result is a laser gain medium with a thermo-mechanical figure of merit of Rs~19,500 Wm−1 a 24-fold and 19,500-fold improvements over the high-energy-laser leaders Nd:YAG (Rs~800 Wm−1) and Nd:Glass (Rs~1 Wm−1), respectively. Moreover, the emission bandwidth of Nd:Al2O3 is broad: ~13 THz. The successful demonstration of gain and high bandwidth in a medium with superior Rs can lead to the development of lasers with previously unobtainable high-peak powers, short pulses, tunability, and high-duty cycles. Transparent ceramics doped with rare-earth atoms have mechanical properties that may help surpass outputs of conventional solid-state lasers. Because laser power is a function of a materials’ thermal conductivity and shock resistance, researchers have investigated robust sapphire crystals as potential platforms for high-energy lasers. Javier Garay and co-workers at the University of California San Diego now report a process that uses elevated heating and cooling rates to incorporate neodymium dopants into sapphire to achieve, optical gain which is necessary for laser amplification. The technique relies on fabricating ceramics composed of nanoscale crystallites, smaller than the laser light wavelength. These nanostructures reduce unwanted light scattering from sapphire’s naturally asymmetric atomic structure, and ensure even dopant distribution. The large, tunable bandwidth of the new sapphire laser could aid applications needing ultra-short, high-power pulses.

/pdf/gain-in-polycrystalline-nd-doped-alumina-leveraging-length-1xlhj6ccgc.pdf

Gain in polycrystalline Nd-doped alumina: leveraging length scales to create a new class of high-energy, short pulse, tunable laser materials

Improved transmittance and ferroelectric properties realized in KNN ceramics via SAN modification

Transparent ultrafine Yb3+:Y2O3 laser ceramics fabricated by spark plasma sintering

The aim was to evaluate the translucency, opalescence, and fluorescence of highly translucent zirconia, lithium disilicate, and bovine teeth. One mm-thick specimens of five monolithic zirconia systems, two glass-ceramics, and bovine enamel/dentin were investigated. A spectrophotometer (Ci7600) was used to measure the CIELab color coordinates, and the translucency and opalescence values were obtained. For evaluating the fluorescence emission, the differences in spectral reflectance by the UV component of illumination were calculated. The microstructures of ceramic specimens were examined with a scanning electron microscope and the chemical compositions were determined with an X-ray fluorescence spectrometer. Mechanical properties were appraised with three-point bending strength, indentation fracture toughness, and Vickers hardness. Data were analyzed using a one-way ANOVA, followed by Tukey's multiple comparison test (α = 0.05). A higher yttria content (5 mol%) significantly improved the translucency of zirconia ceramics, while they were less translucent than lithium disilicate (p < 0.05). Lowering the alumina content below 0.05 wt.% enhanced the translucency (p < 0.05), but a small amount of alumina was still required to obtain full densification. 0.05 wt.% Fe was used to increase the chroma of zirconia specimens without compromising their mechanical properties. The Er-containing zirconia specimen showed a maximal fluorescence emission at 430 nm. The degree of opalescence was affected by the microstructures of ceramic materials. The microstructure, incorporation of a secondary phase, and sintering behavior can have a strong impact on the final mechanical and optical properties of dental ceramics. Addition of small amounts of metal oxides can affect the translucency, opalescence or fluorescence qualities of zirconia.

https://www.mdpi.com/1996-1944/13/15/3395/pdf

Optical and Mechanical Properties of Highly Translucent Dental Zirconia

Light scattering due to birefringence has prevented the use of polycrystalline ceramics with anisotropic optical properties in applications such as laser gain media. However, continued development of processing technology has allowed for very low porosity and fine grains, significantly improving transparency and is paving the way for polycrystalline ceramics to be used in demanding optical applications. We present a method for producing highly transparent Cr3+ doped Al2O3 (ruby) using current activated pressure assisted densification. The one-step doping/densification process produces fine grained ceramics with well integrated (doped) Cr, resulting in good absorption and emission. In order to explain the light transmission properties, we extend the analytical model based on the Rayleigh-Gans-Debye approximation that has been previously used for undoped alumina to include absorption. The model presented captures reflection, scattering, and absorption phenomena in the ceramics. Comparison with measured tran...

The role of scattering and absorption on the optical properties of birefringent polycrystalline ceramics: Modeling and experiments on ruby (Cr:Al2O3)

We present a method for the preparation of transparent Tb doped zirconia (Tb:ZrO2) ceramics that luminesce in the visible. The visible luminescence is temperature dependent, yielding samples that have integrated temperatures sensing capabilities. Our approach is to simultaneously react and densify ZrO2 and Tb4O7 using current activated pressure assisted densification (CAPAD). The Tb dopant serves to both stabilize the tetragonal phase of zirconia and for emitting light. The Tb:ZrO2 ceramics have an excellent combination of structural and optical properties; the toughness is comparable to yttria stabilized zirconia and the transparency in the visible is high. Moreover, the luminescent lifetimes are long and amenable to luminescent thermometry. The ceramics have promise as thermal barrier materials and high-strength windows with “built-in” temperature measurement capabilities.

Transparent, luminescent terbium doped zirconia: development of optical-structural ceramics with integrated temperature measurement functionalities

Light induced absorption and optical sensitizing of Sn2P2S6:Sb

The photorefractive effect in Sn2P2S6 (SPS) is caused by a spatial redistribution of both positively charged and negatively charged carriers, which leads to the formation of two out-of-phase space charge gratings that partially compensate each other in the steady state. The unusual intensity dependence of the compensation grating buildup time is reported in this article for antimony doped SPS; it is explained by the thermal excitation of electrons into conduction band from the optically recharged Sb3+ → Sb2+ impurity ions.

Temporal dynamics of two-beam coupling and the origin of compensation photorefractive gratings in Sn_2P_2S_6:Sb

Methods are disclosed for separating and harvesting very small single domain ferroelectric nanoparticles by application of a non-uniform electric or magnetic field gradient. The disclosed methods enable collection of nanoparticles with permanent strong dipole moments for use in a wide variety of applications with greatly improved results.

Sergey Basun

Papers

The role of scattering and absorption on the optical properties of birefringent polycrystalline ceramics: Modeling and experiments on ruby (Cr:Al2O3)

Transparent, luminescent terbium doped zirconia: development of optical-structural ceramics with integrated temperature measurement functionalities

Light induced absorption and optical sensitizing of Sn2P2S6:Sb

Temporal dynamics of two-beam coupling and the origin of compensation photorefractive gratings in Sn_2P_2S_6:Sb

Harvesting single domain nanoparticles and their applications