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All sources NASA NTRS DOE OSTI

DOE OSTI2015

Study of structural and optical properties of YAG and Nd:YAG single crystals

Highlights: • Transparent YAG and pale pink Nd:YAG single crystals were produced by the Czochralski technique. • Growth mechanisms and shape of the liquid/solid interface and incorporation of Nd{sup 3+} were studied. • The structure of the crystals was investigated by X-ray diffraction, Raman and IR spectroscopy. • The 15 Raman and 17 IR modes were observed. • The obtained YAG and Nd:YAG single crystals were without core and of good optical quality. - Abstract: Yttrium aluminum garnet (YAG, Y{sub 3}Al{sub 5}O{sub 12}) and yttrium aluminum garnet doped with neodymium (Nd:YAG) single crystals were grown by the Czochralski technique. The critical diameter and the critical rate of rotation were calculated. Suitable polishing and etching solutions were determined. As a result of our experiments, the transparent YAG and pale pink Nd:YAG single crystals were produced. The obtained crystals were studied by X-ray diffraction, Raman and IR spectroscopy. The crystal structure was confirmed by XRD. The 15 Raman and 17 IR modes were observed. The Raman and IR spectroscopy results are in accordance with X-ray diffraction analysis. The obtained YAG and Nd:YAG single crystals were without core and of good optical quality. The absence of a core was confirmed by viewing polished crystal slices. Also, it is important to emphasize that the obtained Nd:YAG single crystal has a concentration of 0.8 wt.% Nd{sup 3+} that is characteristic for laser materials.

36 MATERIALS SCIENCE↗

DOE OSTI2018

Strong photoluminescence emission at low dopant amount in YAG:Ce and YAG:Eu phosphors

Highlights: • YAG:Ce and YAG:Eu materials were prepared by solid state reaction. • Pure YAG phase can be obtained at 1300 °C. • High density materials were synthesized at 1600 °C for 10 h. • The highest PL emission was observed for the YAG:Ce{sub 0.01} and YAG:Eu{sub 0.1} samples. - Abstract: YAG:Ce and YAG:Eu phosphors have been prepared by solid state reaction. The use of submicrometric powders allows preparing pellets with high density, enhancing the photoluminescence (PL) properties. Pellets were prepared by uniaxial pressing and the influence of the thermal treatment on the microstructural and optical properties were also studied. Pure YAG phase was obtained at 1400 °C during 1 h and high density pellets (97%) after sintering at 1600 °C for 10 h. The highest PL emission was achieved for the sintered YAG:Ce and YAG:Eu pellets doped with low dopant concentrations (0.01 mol% for Ce and 0.1 mol% for Eu). Finally, increasing the Ce and Eu concentration the PL intensity decreases and the dopants occupy different positions than the Y one in the YAG lattice.

36 MATERIALS SCIENCE↗

DOE OSTI2015

Thin-disk laser based on an Yb:YAG / YAG composite active element

A thin-disk laser module based on an Yb:YAG / YAG composite active element is developed with a small-signal gain of 1.25 and a stored energy of 400 mJ under cw pumping. The gain and thermally induced phase distortions in the module are studied experimentally. Based on this module, a thin-disk laser with an average power of 300 W and a slope efficiency of 42% is designed. (lasers)

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

DOE OSTI2020

Laser induced damage in coatings for cryogenic Yb:YAG active mirror amplifiers

We report results of a study of the laser induced damage threshold (LIDT) behavior of ion beam sputtered H f O 2 / S i O 2 multilayer coatings on Yb:YAG using 1-on-1 and N-on-1 test protocols. The tests were conducted at ambient, vacuum, and cryogenic conditions using 280 ps pulses at λ <#comment/> = 1030 n m . The 1-on-1 LIDT of antireflection (AR) stacks is found to be only slightly reduced under vacuum and cryogenic conditions, while that of high reflectivity (HR) stacks is insensitive to environmental conditions within the uncertainty of the measurements. Cryogenic N-on-1 tests show the LIDT of the HR coating is almost the same as in the 1-on-1 tests. Conversely, the cryogenic N-on-1 test of the AR coating shows damage at ∼ <#comment/> 13 J / c m 2 , a fluence lower than the 20.4 J / c m 2 of 1-on-1 tests. The AR damage behavior is found to be affected by imperfections at the Yb:YAG surface. These findings show that high surface quality is required to increase energy extraction from active mirror laser amplifiers.

Wang, Hanchen↗

DOE OSTI2016

Evaluation of a commercially available passively Q-switched Nd:YAG laser with LiF:F-2(-) saturable absorber for laser-induced breakdown spectroscopy

Interest in passively Q-switched microchip lasers as a means for miniaturization of laser-induced breakdown spectroscopy (LIBS) apparatus has rapidly grown in the last years. To explore the possibility of using a comparatively UV-Vis transparent absorber, we herein present the first report on the evaluation of a commercially available flash lamp-pumped passively Q-switched Nd:YAG laser with LiF:F 2 - saturable absorber as an excitation source in LIBS. Quantitative measurements of barium, strontium, rubidium and lithium in granite, rhyolite, basalt and syenite whole-rock glass samples were performed. Ablation craters produced on a rock glass sample were characterized using a computerized X-ray tomography. Using a gated intensified benchtop spectrometer, limits of detection of 0.97, 23, 37, and 144 ppm were obtained for Li, Sr, Rb, and Ba, respectively. Finally, we discuss the advantages of using such a laser unit for LIBS applications in terms of ablation efficiency, analytical performances, output energy, and standoff capabilities.

36 MATERIALS SCIENCE↗

DOE OSTI2019

Dual-wavelength Q-switched laser based on a lens-shaped Nd : YAG active element and a Cr{sup 4+}: YAG passive Q-switch

Dual-wavelength Q-switched lasing at wavelengths of 1047 and 1053 nm is achieved in a longitudinally diode-pumped laser with a lens-shaped Nd:YLF active element and a Cr{sup 4+} : YAG passive Q-switch. Dual-wavelength lasing is achieved as a result of transverse mode locking due to the choice of a cavity length corresponding to the close-to-semiconfocal configuration, which provides identical gains for the two laser wavelengths. (lasers)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2016

A flux-free method for synthesis of Ce{sup 3+}-doped YAG phosphor for white LEDs

Highlights: • A series of CeF{sub 3}-doped YAG phosphors were successfully synthesized. • CeF{sub 3} not only can be used as the Ce{sup 3+} source but also can play the role of a flux. • The QY of YAG:CeF{sub 3} phosphor is 91% but the QY of YAG:Ce{sub 2}O{sub 3} phosphor is just 80%. • YAG:CeF{sub 3} phosphor exhibits excellent thermal stability. • Using CeF{sub 3} as the Ce{sup 3+} source is a promising flux-free method to prepare YAG:Ce{sup 3+}. - Abstract: A series of CeF{sub 3}-doped Y{sub 3}Al{sub 5}O{sub 12} (YAG:CeF{sub 3}) phosphor, CeO{sub 2}-doped Y{sub 3}Al{sub 5}O{sub 12} (YAG:Ce{sub 2}O{sub 3}) phosphor and 5 wt% BaF{sub 2} added YAG:Ce{sub 2}O{sub 3} (YAG:Ce{sub 2}O{sub 3} + BaF{sub 2}) phosphor were successfully synthesized by a solid-state reaction method. The microstructure, morphology, luminescence spectra, luminescence quantum yield (QY) and thermal quenching of the phosphors were investigated. The QY of YAG:CeF{sub 3} phosphor is 91% but the QY of YAG:Ce{sub 2}O{sub 3} phosphor is just 80%. At 150 °C, the luminescence intensity of YAG:CeF{sub 3} phosphor, YAG:Ce{sub 2}O{sub 3} phosphor and YAG:Ce{sub 2}O{sub 3} + BaF{sub 2} phosphor was 85%, 86% and 89% of that measured at 25 °C, respectively. The comprehensive performance of the white LED lamp employing YAG:CeF{sub 3} phosphor is even better than that of the white LED lamp employing YAG:Ce{sub 2}O{sub 3} + BaF{sub 2} phosphor. The experimental results show that it is a promising flux-free method to synthesize Ce{sup 3+}-doped YAG phosphor by employing CeF{sub 3} as the Ce{sup 3+} source.

36 MATERIALS SCIENCE↗

DOE OSTI2018

Mn4+/Zn2+:YAG glass ceramic for light emitting devices

Highlights: • Luminescence of Mn{sup 4+}:YAG red phosphor was enhanced via Zn{sup 2+} doping. • Mn{sup 4+}/Zn{sup 2+}:YAG GC was successfully prepared via one-step low temperature co-sintering technique. • A series of lighting device was achieved by coupling the Mn{sup 4+}/Zn{sup 2+}:YAG GC with the commercial blue chips and Ce{sup 3+}:LuAG GC. - Abstract: The rare-earth-free Mn{sup 4+}-activated oxide red phosphors draw great attention for their potential applications in the field of light-emitting diodes (LEDs). In this work, the red-emitting Mn{sup 4+}/Zn{sup 2+}:Y{sub 3}Al{sub 5}O{sub 12} phosphor, showing strong red emission peaked at ∼ 672 nm as a result of the spin-forbidden {sup 2}E{sub 2g} → {sup 4}A{sub 2g} electron transition of Mn{sup 4+} ions under 478 nm excitation, was synthesized by a traditional solid-state reaction route in air. The microstructure and luminescent performance of this red-emission phosphor was investigated in detail. From the experimentally measured spectroscopic data, the crystal field strength (Dq) and the Racah parameters B and C were calculated, respectively. In addition, Zn{sup 2+} dopant was found to be beneficial for enhancing Mn{sup 4+} luminescence. Subsequently, Mn{sup 4+}/Zn{sup 2+}:YAG glass ceramic was successfully prepared via using Mn{sup 4+}/Zn{sup 2+}:YAG phosphors incorporated into tellurate glass. A tunable lighting device was successfully achieved by coupling the red-emitting Mn{sup 4+}/Zn{sup 2+}:YAG GC with the commercial blue chips and Ce{sup 3+}:Lu{sub 3}Al{sub 5}O{sub 12} GC.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2017

CMAS behavior of yttrium aluminum garnet (YAG) and yttria-stabilized zirconia (YSZ) thermal barrier coatings

Calcium magnesium aluminosilicate (CMAS) that is formed from the ingested deposits in gas turbines degrades thermal barrier coatings (TBCs), especially for the most widely used material; yttria-stabilized zirconia (YSZ). In the present work, we examine the behavior of yttrium aluminum garnet (YAG) as an alternative material for TBCs. CMAS interaction studies were conducted by making composite pellets of YAG-CMAS and YSZ-CMAS powders. These pellets, after being subjected to heat treatment between 1100 °C and 1500 °C were characterized by X-ray Diffraction (XRD), scanning electron microscopy (SEM) and Energy-dispersive X-ray spectroscopy (EDS), which showed YAG to be almost inert to CMAS whereas YSZ exhibited significant phase changes. To test the behavior of TBCs with YAG and 8YSZ as the topcoat material in a CMAS environment, cyclic furnace tests were conducted in which a controlled amount of CMAS was applied and then the samples were cycled to failure. In addition, to simulate the continuous accumulation of CMAS expected in service, a cyclic furnace test was devised in which a small dose of aqueous solution of CMAS was applied on TBC specimens at the start of every cycle until the samples were cycled to failure. In all these tests YAG TBCs outperformed YSZ in terms of durability. In conclusion, the mechanisms of CMAS attack are described and the relative resistance of YAG and YSZ is shown to be consistent with the Optical Basicity (OB) theory.

36 MATERIALS SCIENCE↗

DOE OSTI2017

Solid-state synthesis of YAG powders through microwave coupling of oxide/carbon particulate mixtures

The rapid synthesis of yttrium aluminum garnet (Y 3 Al 15 O 12 , YAG) powder was investigated through the use of microwave irradiation of the oxide precursor system. For this investigation, an external hybrid heating source was not used. Instead, the rapid heating of the precursor materials (yttria and alumina powders, which are typically transparent to 2.45 GHz microwaves) was initiated by mixing an intrinsic absorbing material (carbon) into the original oxide precursors. The effect of the carbon characteristics, such as carbon source, concentration, particle size, and agglomerate microstructure were evaluated on the efficiency of coupling and resultant oxide reaction. The microwave power was varied to optimize the YAG conversion and eliminate intermediate phase formation. Interactions between the conductive carbon particles and the dielectric oxides within the microwave exposure produced local arching and micro-plasma formation within the powder bed, resulting in the rapid formation of the refractory YAG composition. This optimal conduction led to temperatures of 1000°C that could be achieved in less than 5 min resulting in the formation of > 90 vol% YAG. The understanding of a conductor/dielectric particulate system here, provided insight into possible application of similar systems where microwave irradiation could be used for enhanced solid-state formation, local melting events, and gas phase reactions with a composite powder media.

36 MATERIALS SCIENCE↗

DOE OSTI2018

A Mg2+-Ge4+ substituting strategy for optimizing color rendering index and luminescence of YAG: Ce3+ phosphors for white LEDs

Highlights: • Mg{sup 2+}-Ge{sup 4+} ion pairs can partially substitute the Al{sup 3+} ions of YAG successfully. With the substitution, the garnet crystal structure remains unchanged. • With increasing Mg{sup 2+}-Ge{sup 4+} ions concentrations, the emission spectra show a progressive red-shift, from 528 to 552 nm (about 24 nm). • In white LEDs, with increasing Mg{sup 2+}-Ge{sup 4+} ions concentrations, the CCT decreased gradually from 6798 to 3261 K and the CRI increased from 76.5 to 89.3. - Abstract: Mg{sup 2+}-Ge{sup 4+} ions substituted YAG: Ce{sup 3+} phosphors (Y{sub 3}Al{sub 5-2x}Mg{sub x}Ge{sub x}O{sub 12}: Ce{sup 3+}) were prepared by high temperature solid state reaction method. X-ray diffraction (XRD), Scanning election microscope (SEM), Photoluminescence (PL) spectra and so on were used to characterize the samples. The effects of Mg{sup 2+}-Ge{sup 4+} concentrations on the morphology, structure, luminescence properties, fluorescence lifetime and white LED performance of YAG: Ce{sup 3+} phosphors were studied in detail. The results indicate that Mg{sup 2+}-Ge{sup 4+} ion pairs can partially substitute the Al{sup 3+} ions of YAG successfully. With the substitution, the garnet crystal structure remains unchanged. However the emission spectra show a progressive red-shift, from 528 to 552 nm (about 24 nm). The lifetime decreased rapidly from 84 to 26 ns. In particular, the correlated color temperature (CCT) decreases gradually from 6798 to 3261 K and the color rendering index (CRI) increases from 76.5 to 89.3 with the increasing of the incorporation content of Mg{sup 2+}-Ge{sup 4+} ion pairs.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2015

Single-frequency, injection-seeded Er:YAG laser based on a bow-tie ring slave resonator

A diode pumped, injection-seeded Q-switched Er:YAG laser at 1645.2 nm is demonstrated. A single frequency Er:YAG monolithic nonplanar ring oscillator (NPRO) laser emitting at 1645.24 nm with a maximum output power of 500 mW is used as a seed laser. The seed laser output is injected into a bow-tie slave laser, obtaining stable single-frequency Q-switched operation of the Er:YAG laser. The maximum single-frequency Q-switched Er:YAG laser output energy is 2.9 mJ at 100 Hz with a pulse duration of 160 ns. (lasers)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2017

Study of lasing on the {sup 4}F{sub 3/2} → {sup 4}I{sub 13/2} secondary transition of Nd{sup 3+} ions in a phase-conjugate Nd{sup 3+} : YAG laser

Lasing at a wavelength of 1.34 µm on the {sup 4}F{sub 3/2} → {sup 4}I{sub 13/2} secondary transition of Nd{sup 3+} ions in a phase-conjugate (PC) Nd{sup 3+} : YAG laser under four-wave mixing in a laser medium is theoretically and experimentally investigated. The influence of the amplified spontaneous emission at a wavelength λ = 1.064 µm on the parameters of phase-conjugate generation of the Nd{sup 3+} : YAG laser at λ = 1.34 µm under passive Q switching by a V{sup 3+} : YAG crystal using two-, three-, and four-loop open cavity schemes is analysed by mathematical simulation. It is shown that there is an optimal initial transmission of a passive Q switch (PQS), the value of which decreases with increasing number of cavity feedback loops. The generation in the Nd{sup 3+} : YAG laser at λ = 1.34 µm with an open PC multiloop cavity is experimentally obtained and studied for the first time. Emission in the form of a train of seven pulses with a total energy of 0.25 J and individual pulse energy and duration of 36 mJ and 150 ns, respectively, is obtained with an initial PQS transmission of 74 %. The angular divergence of the laser beam is found to be 0.7 mrad at quality factors M{sub x}{sup 2}=1.2 and M{sub y}{sup 2}=1.1. (paper)

42 ENGINEERING↗

DOE OSTI2021

Material jet printing of transparent ceramic Yb:YAG planar waveguides

A new, to the best of our knowledge, 3D additive manufacturing technique utilizing particle-loaded ink jet printing to fabricate transparent ceramic Yb:YAG planar waveguides for laser gain media was demonstrated. Rheological optimization of YAG particle-loaded inks resulted in successful droplet formation and printing resolution. Planar waveguides composed of a Yb:YAG guide encased in undoped YAG cladding were printed with guide thicknesses ranging between 25 and 350 µm and consolidated to high optical quality via solid-state sintering. Sufficiently low optical (1–3%/cm) and intermodal scatter allowed single-mode propagation with a core/clad index difference of Δ n ∼ 5.0 × 10 − 4 (corresponding to 3 at.% Yb). The waveguides were cladding-pumped longitudinally with a 940 nm diode array resulting in 23.6% slope efficiency in 2 ms pulsed operation.

36 MATERIALS SCIENCE↗

DOE OSTI2022

($\mathrm{INVITED}$)Counter-ion effect on the diffusion behavior of $\mathrm{Y}$b, $\mathrm{L}$u, and $\mathrm{N}$d ions in $\mathrm{YAG}$ transparent ceramics

The ability to fabricate additively manufactured laser waveguides with sharp dopant concentration interfaces is limited by diffusion of the dopants at the temperatures required to fully densify the material. Compositional analysis of bilayer samples, where each layer was either undoped YAG or YAG doped with Yb, Lu, or Nd, were fabricated such that all combinations were available for testing. Samples were fabricated at both 1750°C and 1850°C to determine the diffusion behavior of each dopant alone and also in the presence of a second dopant. It was found that the experimental concentration profiles exhibited both intragranular (bulk) and grain boundary contributions, and thus fitting to a complementary error function equation required the use of two diffusion coefficients. Nd always diffused further along grain boundaries than the other dopants, due in part to its small segregation coefficient in YAG. It is shown that the presence of Nd as a counter dopant inhibits intragranular diffusion of other dopants while enhancing their grain boundary diffusion. All the observed trends were attributed to a combination of intragranular lattice strain due to: dopant ions replacing yttrium substitutionally, the relative driving forces for the segregation of dopant ions to grain boundaries, and the ability of one dopant to affect the diffusion of a different dopant in the other direction to maintain charge neutrality.

36 MATERIALS SCIENCE↗

DOE OSTI2023

Highly Nonstoichiometric YAG Ceramics with Modified Luminescence Properties

Abstract Y 3 Al 5 O 12 (YAG) is a widely used phosphor host. Its optical properties are controlled by chemical substitution at its YO 8 or AlO 6 /AlO 4 sublattices, with emission wavelengths defined by rare‐earth and transition‐metal dopants that have been explored extensively. Nonstoichiometric compositions Y 3+x Al 5‐x O 12 ( x ≠ 0) may offer a route to new emission wavelengths by distributing dopants over two or more sublattices simultaneously, producing new local coordination environments for the activator ions. However, YAG typically behaves as a line phase, and such compositions are therefore challenging to synthesize. Here, a series of highly nonstoichiometric Y 3+x Al 5‐x O 12 with 0 ≤ x ≤ 0.40 is reported, corresponding to ≤20% of the AlO 6 sublattice substituted by Y 3+ , synthesized by advanced melt‐quenching techniques. This impacts the up‐conversion luminescence of Yb 3+ /Er 3+ ‐doped systems, whose yellow‐green emission differs from the red‐orange emission of their stoichiometric counterparts. In contrast, the YAG:Ce 3+ system has a different structural response to nonstoichiometry and its down‐conversion emission is only weakly affected. Analogous highly nonstoichiometric systems should be obtainable for a range of garnet materials, demonstrated here by the synthesis of Gd 3.2 Al 4.8 O 12 and Gd 3.2 Ga 4.8 O 12 . This opens pathways to property tuning by control of host stoichiometry, and the prospect of improved performance or new applications for garnet‐type materials.

Chemistry↗

DOE OSTI2021

Multi-octave-spanning supercontinuum generation through high-energy laser filaments in YAG and ZnSe pumped by a 2.4 μm femtosecond Cr:ZnSe laser

Abstract We present experimental and numerical investigations of high-energy mid-infrared filamentation with multi-octave-spanning supercontinuum generation (SCG), pumped by a 2.4 μm, 250 fs Cr:ZnSe chirped-pulse laser amplifier. The SCG is demonstrated in both anomalous and normal dispersion regimes with YAG and polycrystalline ZnSe, respectively. The formation of stable and robust single filaments along with the visible-to-mid-infrared SCG is obtained with a pump energy of up to 100 μJ in a 6-mm-long YAG medium. To the best of the authors’ knowledge, this is the highest-energy multi-octave-spanning SCG from a laser filament in a solid. On the other hand, the SCG and even-harmonic generation based on random quasi-phase matching (RQPM) are simultaneously observed from the single filaments in a 6-mm-long polycrystalline ZnSe medium with a pump energy of up to 15 μJ. The numerical simulations based on unidirectional pulse propagation equation and RQPM show excellent agreement with the measured multi-octave-spanning SCG and even-harmonic generation. They also reveal the temporal structure of mid-infrared filaments, such as soliton-like self-compression in YAG and pulse broadening in ZnSe.

Optics↗

DOE OSTI2015

Numerical estimation of phase transformations in solid state during Yb:YAG laser heating of steel sheets

This work concerns the numerical modeling of heat transfer and phase transformations in solid state occurring during the Yb:YAG laser beam heating process. The temperature field is obtained by the numerical solution into transient heat transfer equation with convective term. The laser beam heat source model is developed using the Kriging interpolation method with experimental measurements of Yb:YAG laser beam profile taken into account. Phase transformations are calculated on the basis of Johnson - Mehl - Avrami (JMA) and Koistinen - Marburger (KM) kinetics models as well as continuous heating transformation (CHT) and continuous cooling transformation (CCT) diagrams for S355 steel. On the basis of developed numerical algorithms 3D computer simulations are performed in order to predict temperature history and phase transformations in Yb:YAG laser heating process.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗