YAG Layers Research Articles

Inkjet Printing of Yb:YAG Transparent Ceramic Planar Waveguide Laser Gain Medium

Herein, a YAG/10 at% Yb:YAG/YAG transparent ceramic planar waveguide (PWG) gain medium has been molded via inkjet printing and dry pressing molding. The composition and rheological property of ink are optimized along with the printing process to enhance the printing accuracy and quality. The PWG has dimensions of 13.5 × 8.0 × 1.8 mm3, while the thickness of the core Yb:YAG layer is ≈190 μm. The in‐line transmittance of the PWG reaches 81.7% at 1030 nm, and the average grain size is ≈2.3 μm. The diffusion characteristics of Yb ions across the interface between the cladding YAG layer and the core Yb:YAG layer are investigated by calculating the diffusion coefficient and the mean diffusion distance of 172Yb ions. The Yb:YAG PWG oscillator, which is pumped from a single end by a 940 nm laser diode, produces continuous wave laser at a wavelength of 1030 nm and exhibits the highest power (3.8 W) and highest absorbed–output slope efficiency (64.6%).

Design of thermal and environmental barrier coatings for Nb-based alloys for high-temperature operation

The design of thermal and environmental barrier coatings (T/EBCs) applied to Nb-based alloys for high-temperature operation (>1200 °C) was studied. Different multilayer T/EBCs consisting of rare earth aluminates, silicates, and zirconates (with Y 3 Al 5 O 12 (YAG), Y 2 SiO 5 (YMS), and Gd 2 Zr 2 O 7 (GZO) as exemplars) are proposed. Mechanics models were used to determine the magnitude of thermal stresses developed and the tendency for delamination or penetration cracking. The calculated energy release rates (ERRs) for crack formation show that the T/EBC composed of a porous YAG layer (porosity > 0.15) and a dense YAG + YMS layer is effective in preventing the delamination and can potentially arrest cracks penetrating from the surface before reaching the substrate. Phase equilibria calculations indicate that all combinations are stable to above their expected use temperatures. The greatest likelihood for melting is the scenario where a YAG + YMS solid mixture contains excess SiO 2 due to process variability, but even in this case the melting temperature, 1430 °C, exceeds the corresponding temperature in the prescribed temperature profile. • Multilayer thermal/environmental barrier coatings inhibit crack growth. • Rare earth aluminate and silicate coatings are suitable for Nb-based alloy. • Phase mixtures have better properties but lower melting temperatures. • Columnar porosity in coating reduces energy release rate for crack formation.

Oxidation Resistance of Double-Ceramic-Layered Thermal Barrier Coating System with an Intermediate Al2O3-YAG Layer

In the present study, APS Al2O3-YAG layers containing 10, 20, and 40 wt.% YAG were deposited as the intermediate layer between the MCrAlY bond coat and the YSZ top coat of double-ceramic-layered TBC (DCL-TBC) on the Ni-based superalloy substrate. Then, the effect of its YAG content on the oxidation behavior of the coated sample was investigated. Microstructural studies of the coatings showed that adding Al2O3-YAG intermediate layer to DCL-TBC system reduced the growth rate and thickness of the TGO layer due to the influence of reactive element, reduction in oxygen inward diffusion, and inhibition in the formation of detrimental mixed oxides as the TGO layer. The cyclic oxidation test at 1050 °C indicated that the oxidation resistance of the coating with the Al2O3-20 wt.% YAG layer was better than that of the other samples.

Composite structure Cr:YAG/Ce:YAG and (Ce,Cr):YAG/Ce:YAG transparent ceramics with high color rendering index for white LEDs/LDs

Transparent ceramics (TCs) with high color rendering index (CRI) are considered as excellent color converters for white light-emitting diode (LED) and laser diode (LD) devices. In this study, by utilizing the component and structural designs between layers, composite structure (Ce,Cr):YAG/Ce:YAG and Cr:YAG/Ce:YAG TCs with high CRI were fabricated by vacuum sintering. Microstructural and luminescence properties, as well as energy transfer from Ce3+ to Cr3+ ions of as-fabricated TCs were explored systematically. Simultaneously, TC based white LEDs/LDs were assembled via the remote excitation mode. Under 460 nm excitation, a high CRI value of 75.2 was realized in (Ce,Cr):YAG/Ce:YAG TC based white LEDs. As increasing the thickness of the Cr:YAG layer in Cr:YAG/Ce:YAG TC, its red emission intensity could be enhanced distinctly. The optimized CRI and CCT values could reach 74.4 and 4146 K, respectively. In addition, the optimized luminous flux (LF) and CRI of Cr:YAG/Ce:YAG TC based LD device were 160.6 lm and 69.1, respectively. Therefore, the composite structure design is an effective approach to realize the essential promotion of CRI value in TC based white LED/LD devices.

Ultrafast formation of Al2O3–Y3Al5O12 eutectic ceramic by flash sintering

AbstractIn this study, a dense Al2O3–Y3Al5O12 (YAG) ceramic was synthesized by flash sintering a powder mixture of Al2O3 and Y2O3 in less than 150 seconds at a furnace temperature of 1350°C. The resultant ceramic has a well‐defined eutectic structure consisting of alternating Al2O3 and YAG layers. The hardness and fracture toughness of the ceramic were measured to be 18.5 GPa and 4.3 MPa.m1/2, respectively. These values are comparable to those of similar eutectic ceramics made by directional solidification techniques. The results suggest a new method for making high‐performance eutectic ceramics, which could be applied in other systems.

Pump coupling optimization of a native inhomogeneous planar waveguide laser

Abstract Planar waveguide laser is a promising candidate for high power solid state lasers. Normally the native inhomogeneous refractive index exists during fabrication process, this will apparently affect power scaling and beam quality. Few quantitative works have been reported to the optimization of this behavior and in practice, try and error routine is needed to set pump conditions. In this work, we manufactured a miniature composite Yb:YAG ceramic waveguide laser via non-aqueous tape casting method, refractivity index gradience is natively generated via border diffusion between the Yb:YAG and YAG layers. We found a simple and effective criterion to treat pump optimization by combining wave optics model and laser rate equations. Guided by this criterion, we obtained an experimental slope-efficiency about 66% with optimized pumping beam parameters. This method could be forward applied in similar designs and much higher power planar waveguide lasers.

Scintillation properties of composite ceramic YAG and its capability on pulse shape descrimination

Transparent ceramic composite of non-doped and Ce-doped YAG was prepared by Konoshima Chemical with the vacuum sintering technique and investigated on pulse shape discrimination capability for functional collimator. Scintillation responses such as X-ray induced radioluminescence and decay time profiles of non-doped and Ce-doped YAG were evaluated. Pulse shape discrimination capability of the composite ceramic was evaluated by 137Cs 662 keV γ-ray irradiation. As a result, clear separation of γ-ray events at non-doped or Ce-doped YAG layers was observed in two dimensional histogram by using signal processing with two different shaping times.

The water vapor hot gas corrosion of MGC materials with Al 2O 3 as a phase constituent in a combustion atmosphere

The hot gas corrosion behavior of two melt grown composite materials (Al 2O 3/YAG and Al 2O 3/GAP) in comparison with alumina and sapphire was investigated. The tests were performed in a high temperature burner rig at 1450 °C, a total pressure of 1 atm with a water vapor partial pressure of 0.28 atm, a gas flow velocity of 100 m/s and exposure times for up to 450 h. In comparison to sapphire, alumina showed comparable corrosion rates and similar corrosion traces on the corroded surface. The Al 2O 3/YAG and Al 2O 3/GAP melt grown composite materials were subject to degradation due to the corrosion attack of the alumina phase. This was the consequence of the formation and evaporation of volatile hydroxides (e.g., Al(OH) 3). In comparison to polycrystalline alumina the YAG or GAP showed a higher corrosion stability, which causes the formation of a porous YAG or GAP surface layer with increasing corrosion time. For short corrosion times, the porous YAG or GAP surface layer led to a small corrosion protection of the material. After longer corrosion times a switch to linear corrosion kinetics was observed due to spalling of the porous corrosion layer. The corrosion rates for long exposure times were comparable to bulk alumina or sapphire. In principle the regarded polycrystalline and single crystalline materials showed the same corrosion behavior.

Liquid-phase epitaxy growth and characterization of Co,Si:YAG thin film saturable absorber

Abstract Thin films of Co,Si:YAG were grown on YAG and Er,Yb:YAG substrates by means of the isothermal liquid-phase epitaxy (LPE) dipping technique. X-ray diffraction analysis, optical transmission spectra measurements, and passive Q-switching experiments were performed to characterize the obtained layers. Absorption saturation measurements of Co,Si:YAG thin films were carried out at 1.54 μm. Passive Q-switching of the Er:glass laser by use of epitaxial Co,Si:YAG/YAG was observed. We demonstrated experimentally that the Co,Si:YAG layers could be used as an effective saturable absorber for the lasers operating near 1.5 μm.

Deposition of Er:YAG (YAP) layers by subpicosecond and nanosecond KrF excimer laser ablation

Thin films of Er:YAG and Er:YAP were deposited by subpicosecond (450 fs) and nanosecond (20 ns) KrF laser ( λ=248 nm) on YAG, YAP, fused silica, silicon and sapphire substrates. Laser spot size, energy density, substrate temperature and deposition ambient (vacuum and oxygen) were varied. Comparison of growth rate, morphology, composition, crystallinity and adhesion of the films grown by subpicosecond and nanosecond deposition is presented.

Detection and removal of surface defects in optical materials

Numerous insulating materials are used as substrates for optical waveguide versions of lasers, second harmonic generation, electro-optics and photonic devices but, independent of the production methods, the losses in the guides are considerably worse than those of bulk material. It is therefore essential to overcome this major problem, not least because success would allow a much wider range of materials to be included in waveguide applications, (e.g. by developing low gain systems such as tuneable laser waveguides). An obvious source of the loss occurs in the cutting and polishing of the surface since, although the outer layer may be optically flat, the subsurface is highly strained and has a high dislocation density to depths of several microns (i.e. precisely in the depth regime where the waveguides are formed). Such dislocation probelms can be revealed and, in the case of Nd : YAG, improvements introduced by amorphisation and chemical etching of the surface, to generate a damage free surface layer. Once the damaged YAG layer was removed cathodoluminecence (CL) intensity increased by 250%, SHG effects were noted, and for waveguides photoluminescence increased by 40% and transmission was improved. The method employed may be applied much more widely (e.g. in garnets, LiNbO3, Quartz and phosphates).

Liquid phase epitaxy: A versatile technique for the development of miniature optical components in single crystal dielectric media

In this paper we will review the possibilities of liquid phase epitaxy (LPE) as a versatile technique for the development of new miniature optical components in single crystal dielectric media. These LPE layers can be used in active waveguide configuration as laser or amplifier sources or in transverse configuration as saturable absorber deposited on an active layer. So in the first part of this paper, we will present the LPE process by describing the growth conditions of rare earths doped YAG layers and by discussing the properties obtained in laser planar waveguides. In a second part, we will discuss some other applications, as amplifiers or saturable absorbers, using LPE layers. In the third and last part, we will present the interest of LPE for other materials, used as laser waveguides.

Growth by LPE of Nd: YAG single crystal layers for waveguide laser applications

Nd:YAG layers, for waveguide laser applications, have been grown by liquid phase epitaxy on [111] YAG substrates from a saturated PbO/B 2 0 3 flux using the horizontal dipping technique. The influence of melt composition on growth conditions is discussed. Some substitutions (gallium, lutetium) were studied with the purpose of optimizing the waveguide properties.

On the saturation of Tb phosphors under cathode-ray excitation. I. Excited-state absorption in Tb-activated phosphor powders

Optical transitions between the 5D4 excited state of the Tb3+ (4f)8 configuration and the crystal-field split components of the (4f)7(5d) configuration are observed using high-resolution laser excitation of Tb-doped powder samples at room temperature. Excited-state absorption spectra of Tb3+ in YAG, YAGaG, Y2SiO5, and LaOBr are presented. Superimposed on the broadband excitation spectrum of these transitions we find the relatively narrow 4f→4f lines. We present a theoretical model for interpreting the 4f→5d transitions, which predicts a strict proportionality between the (4f)8 5D4→(4f)7(5d) and the (4f)8 7F6→(4f)7(5d) transitions. This model is used to estimate the optical-absorption cross section for the former transitions. Although the terminating 4f levels lie at the same energy as the 5d bands, the 4f→4f transitions can be interpreted on the basis of the Judd-Ofelt theory. We derived a method for calibration of the Tb3+ 4f→5d fluorescence-excitation spectra from powder samples. For YAG:Tb, the resulting optical cross sections were confirmed by direct-absorption measurements on a Tb3+ -doped epitaxial YAG layer. To our knowledge, this is the first time that the probabilities for excited-state absorption to highly excited 5d and 4f states in Tb3+ have been obtained theoretically and experimentally from Tb-doped powder materials.

Novel technique of phosphor deposition to form cathode-ray-tube screens

We developed a new phosphor deposition technique for CRT display applications. In this new technique, phosphor powder was treated in H <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> SO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</inf> , deposited on a substrate, and heated between 320 and 780°C for about 1 to 2 h in O <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> . XRD and TGA analyses showed that a sulfate phase was formed by this treatment, and the sulfate phase served as a binder and increased the contact area between adjacent YAG particles and between the YAG layer and the substrate as shown by SEM studies. Furthermore, phosphor layers prepared by our novel technique were about 10 percent higher in cathodoluminescence than those prepared by the conventional settling technique.

Epitaxially grown monocrystalline garnet cathode-ray tube phosphor screens

The technique of liquid phase epitaxy has been used to produce single-crystal garnet phosphor screens for cathode ray tubes. The films were rare-earth-doped yttrium aluminum garnets (YAG’s) grown onto YAG substrates using a PbO:B2O3 flux. We have studied the light output of these layers as a function of film growth temperature, rare-earth activator concentration, and incident power density. With Ce:YAG layers it was possible to use beam power densities up to 108 W/m2 and this produced a radiance of over 105 W/cm2 sr.

Liquid phase epitaxy of Nd 3+ doped YAG layers by the dipping technique

With a growth rate up to 2 μm/min epitaxial layers of Nd 3+ doped yttrium aluminum garnets (Nd : YAG) were grown on pure one inch diameter YAG substrates for application in integrated optics by liquid phase epitaxy using the horizontal dipping technique. The quality of the layers up to 150 μm in thickness was examined optically, by X-ray photographs, by microprobe and by cathodoluminescence analysis. The layers are waterclear, free of cracks and strains, and have a smooth surface. The planity of the interface substrate/layer is of high quality. The layers are suitable for waveguides and laser application. Stimulated emission of radiation was measured.