Laser welding can make ceramics integral components in devices for harsh environments as well as in optoelectronic and/or electronic packages needing visible-radio frequency transparency.
We will discuss an ultrafast pulsed laser welding approach that relies on focusing light on interfaces to ensure an optical interaction volume in ceramics to stimulate nonlinear absorption processes, causing localized melting rather than ablation. We will begin by comparing laser joining of glasses and ceramics. We will then introduce various methods for controlling the absorption and scattering properties for ceramics because the key to the technique is the interplay between linear and nonlinear optical properties and laser energy–material coupling. Finally, we will discuss results of laser material interaction on various oxide ceramics.
Rare earth iron garnets (REIG’s) are important component materials in magnetic insulator based spintronics due to their low spin wave damping and electrically insulating properties. Yttrium iron garnet (YIG) has been the mainstay material because of its unusually low spin damping. However, YIG thin films thus far have in-plane magnetization. Recent studies on thulium iron garnet (TIG) thin films have demonstrated robust perpendicular magnetic anisotropy (PMA), however, spin damping in TIG films is significantly higher compared to YIG. It would be useful to have an insulating magnetic material that exhibits both low spin damping and robust, tunable PMA because of its potential for novel device configurations. In this study, we synthesized YIG-TIG solid solution powders across the compositional phase diagram and with different particle sizes using the polymeric steric entrapment technique in order to begin to decouple compositional effects from size and morphological effects. Powder characterization, including XRD, VSM, SEM and FMR techniques, was also performed to understand their magnetic behavior.
We present a systematic study investigating yttria dopant concentrations effects on crystal phase compositions of zirconium dioxide (ZrO2) and the respective bulk optical properties. (ZrO2), a traditional structural ceramic possesses excellent mechanical properties, while simultaneously possessing a wide band gap (5-7eV). This combination of properties opens the door for designs and fabrication of transparent structural ceramics. We use Current-Assisted Pressure Activated Densification (CAPAD), to achieve high heating rates, and comparatively short hold-times, which leads to ceramics with very fine grain sizes. This affords the opportunity to investigate, the effects of yttria dopant concentration on the resultant microstructure (grain size, phases and phase ratios).
Conventional materials engineering approaches for polycrystalline ceramic gain media rely on optically isotropic crystals with high equilibrium solubility of luminescent rare-earth (RE) ions. Crystallographic optical symmetry is traditionally relied upon to avoid scattering losses caused by refractive index mismatch at grain boundaries in randomly oriented anisotropic crystals and high-equilibrium RE-solubility is needed to produce sufficient photoluminescence (PL) for amplification and oscillation. These requirements exclude materials such as polycrystalline sapphire/alumina that have significantly superior thermo-mechanical properties (Rs~19,500Wm-1), because it possesses 1) uxiaxial optical properties that at large grain sizes, result in significant grain boundary scattering, and 2) a very low (~10-3%) RE equilibrium solubility that prohibits suitable PL. I present new materials engineering approaches operating far from thermodynamic equilibrium to produce a bulk Nd:Al2O3 medium with optical gain suitable for amplification/lasing. The key insight relies on tailoring the crystallite size to the other important length scales-wavelength of light and interatomic dopant distances and show that fine crystallite sizes result in sufficiently low optical losses and over-equilibrium levels of optically active RE-ions, the combination of which results in gain. The emission bandwidth is broad, ~13THz, a new record for Nd3+ transitions, enabling tuning from ~1050nm-1100nm and/or ultra-short pulses in a host with superior thermal-mechanical figure of merit. Laser grade Nd:Al2O3 opens a pathway for lasers with revolutionary performance.
KEYWORDS: Zirconium dioxide, Transparency, In vivo imaging, Transmittance, Ceramics, Temperature metrology, Brain, Skull, Thermography, Diagnostics and therapeutics
Laser-based diagnostics and therapeutics show promise for many neurological disorders. However, the poor transparency of cranial bone limits the spatial resolution and interaction depth that can be achieved. We addressed this limitation previously, by introducing a novel cranial prosthesis made of a transparent nanocrystalline yttria-stabilized zirconia (nc-YSZ) which aims to enhance the diagnosis and treatment of neurological diseases by providing chronic optical access to the brain. By using optical coherence tomography, we have demonstrated the initial feasibility of ncYSZ implants for cortical imaging in an acute murine model. Although zirconia-based implants have been known for their excellent mechanical properties, the in vivo application was found to be affected by long-term failures, due to low temperature degradation. Accelerated aging simulations in humid environments at slightly elevated temperatures and over long periods typically transforms the ceramic surface into a monoclinic structure through a stress-corrosion-type mechanism. It was expected that the new nc-YSZ would show sufficient resistance to humid environments in comparison to the conventional zirconia implant. However, even a modest amount of transformation can change optical characteristics such as transparency. Herein we present the results of a simulated ageing study following the guidelines from the ISO 13356:2008 on aging of surgical zirconia ceramics. Comparison of %monoclinic transformation, optical transparency and mechanical hardness of nc-YSZ samples at baseline and following 25 and 100 h hydrothermal treatments shows our implant can withstand these extended ageing treatments.
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