Qingli Zhang

Internal radiation in yttrium aluminum garnet (YAG) crystal and melt significantly influences the morphology of the melt–crystal (m-c) interface during crystal growth. However, radiation absorption coefficients are difficult to measure directly under high-temperature conditions, and consequently, reliable radiation parameters suitable for numerical simulations of YAG crystal growth remain lacking. In this study, the effective radiative absorption coefficients of YAG crystal and melt were inversely determined by combining numerical simulations with crystal-growth and rapid pull-out experiments. A globally coupled multiphysics model for Czochralski growth of YAG crystals was developed using ANSYS Fluent 2024 R2, incorporating electromagnetic induction heating, PID-based heat-source control, and dynamic adjustment of the m-c interface through user-defined functions (UDFs) and user-defined scalars (UDSs). The effects of the absorption coefficients of YAG crystal and melt on the m-c interface morphology were systematically investigated. Comparison with experimental interface morphologies indicated an effective absorption coefficient of 20 m⁻¹ for undoped YAG crystal and that the melt could reasonably be treated as an opaque medium. The experimentally obtained interface morphologies of undoped YAG, 1 at.% Nd:YAG, and 1.46 at.% Yb:YAG were highly consistent, indicating limited effects of Nd³⁺ and Yb³⁺ doping at the investigated concentrations. Thus, the same radiation parameters can reasonably be adopted for these lightly doped crystals.

Yb:Lu3Ga5O12 crystals have attracted considerable interest for tunable solid-state and ultrashort-pulse laser applications owing to their broad absorption and emission bandwidths. However, the high volatility of the Ga2O3 component during crystal growth readily causes deviations of the melt composition from stoichiometry and promotes the formation of crystal defects, thereby limiting the growth of high-quality crystals and the improvement of laser performance. In this work, Yb:LuGG single crystals were grown by the Czochralski method, and their local electronic structure, physical properties, lattice dynamics, and defect characteristics were systematically investigated through a combination of experimental characterization and first-principles calculations. The electron localization function (ELF) and charge-density difference analyses reveal that electrons are predominantly localized around O atoms, while the Yb/Lu/Ga−O bonds are primarily ionic with a certain degree of covalent character. Experimentally, the crystal exhibits a density of 7.75 g·cm−3, a Vickers hardness of 1140 kg·mm−2, a Mohs hardness of 7.05, and a room-temperature thermal conductivity of 4.40 W·m−1·K−1. No imaginary phonon frequencies are observed in the phonon dispersion curves, indicating good dynamical stability of the LuGG crystal. Moreover, the calculated infrared and Raman vibrational modes are in good agreement with the experimental results. Chemical etching experiments combined with surface-energy calculations demonstrate that the (100) plane possesses the highest stability, whereas the (111) plane is the most susceptible to chemical corrosion. Furthermore, positron annihilation lifetime spectroscopy, oxygen-vacancy formation-energy calculations, electron paramagnetic resonance spectroscopy, and optical transmission spectroscopy collectively confirm the presence of oxygen vacancies, while post-growth annealing effectively reduces oxygen-vacancy-related signals. These findings provide both theoretical insights and experimental evidence for understanding the structural stability, defect formation mechanisms, and performance optimization of Yb:LuGG crystals.

In this study, molecular dynamics simulations combined with Raman spectroscopic characterization were employed to investigate the local coordination environments, oxygen coordination states, polyhedral connectivity, and network polymerization characteristics in binary Al2O3–Y2O3 glasses within the composition range of 60–75 mol % Al2O3. Comprehensive analysis of the radial distribution function, coordination number distribution, and angular distribution function has been used to characterize the short-range ordered structures of Al–O and Y–O and to elucidate the distribution characteristics of aluminum–oxygen structure units such as [AlO4], [AlO5], and [AlO6]. Furthermore, the evolution of corner-sharing and edge-sharing behaviors, revealed by bond-angle variations, has been identified. Distributions of oxygen species and Qi species further revealed the evolution of glass network connectivity with composition variation. Deconvolution of Raman spectra in the high-wavenumber region enabled the quantitative analysis of microstructure species. This study provided a comprehensive understanding of the structure evolution in Al-rich binary Al2O3–Y2O3 glasses, establishing a theoretical foundation for the rational network design.

By integrating in situ Raman spectroscopy and theoretical simulations, ring-size-specific Raman signatures are resolved, revealing a highly polymerized molten GeO ₂ network dominated by six-membered rings.

Rare-earth-ion-doped disordered crystals are an effective route to spectral broadening. In this study, high-quality Nd:Lu(x)Y(3-x)Ga5O12 composite laser crystals were grown using the Czochralski method. The crystal dimensions were Ø30 × 90 mm2, and the structure of the Nd:LuYGG crystal was characterized using X-ray diffraction (XRD), XRC, scanning electron microscope (SEM), and ICP-MS. Raman spectroscopy was performed to identify vibrational modes, with the maximum phonon energy determined to be 762.1 cm–1. Absorption, fluorescence spectra, and fluorescence lifetime were measured, revealing that the Nd:LuYGG crystal exhibits pronounced inhomogeneous broadening. Spectroscopic parameters were calculated based on Judd-Ofelt theory. Furthermore, laser experiments generated triple-wavelength outputs at 1058, 1060, and 1066 nm, where a maximum output power of 5.47 W and a slope efficiency of 23.0% were achieved. The broad spectral bandwidth and multiwavelength output demonstrate that the Nd:LuYGG crystal is a material with significant potential for applications in terahertz radiation, tunable lasers, and ultrashort-pulse laser systems.

Er³⁺-doped yttrium aluminium garnet (Er:YAG) is a vital gain medium for 2.9 μm lasers. Understanding its melt properties and structure is essential for elucidating crystal-growth mechanisms and guiding process design. We measured the density, viscosity, and surface tension of 20 at% Er:YAG melt using aerodynamic levitation, established temperature dependences, and validated the results through molecular dynamics (MD) simulations. Furthermore, we build MD models of 20 at% and 50 at% Er:YAG melts in LAMMPS and compute radial distribution functions and coordination numbers for Y, Er and Al. The results show that the mean bond length remains nearly constant at high temperature, whereas the local structure becomes progressively more disordered with increasing temperature, confirming temperature as a key control parameter for short-range order. We also find that Er³⁺ can readily substitute for Y³⁺ in the melt, which helps explain the observed temperature dependences of the macroscopic density and viscosity. Finally, using the measured density, viscosity and surface tension, we develop a two-dimensional axisymmetric steady-state model to systematically analyse how the rotation rate, pulling rate and insulation-structure parameters (thickness, height and aperture) affect the temperature field, flow field and the shape of the solid–liquid interface. Simulations indicate that using Er:YAG-specific parameters, rather than YAG data, leads to markedly different flow patterns and interface morphologies under varying growth conditions. This difference implies that substituting YAG parameters for Er:YAG can introduce substantial errors in growth simulations, underscoring the importance of measuring high-temperature properties of Er-doped YAG melts for accurate modelling of crystal growth. Under the optimised conditions suggested by the simulations, we grow a 20 at% Er:YAG single crystal with dimensions of 80 mm × 100 mm.

This study aims to elucidate the structural evolution of Ta⁵⁺ in the binary Li₂O-Ta₂O₅ melts. The melt structure was characterized by using in situ high-temperature Raman spectroscopy. Combined with constructed Ta-O cluster models and quantum chemistry ab initio calculations to simulate Raman spectra, quantitative analysis of different coordination structures in melts was achieved by the deconvolution of the experimental spectra. Furthermore, the influence of Li₂O content on melt microstructure was systematically investigated via high-energy X-ray scattering and empirical potential structure refinement simulations. Results reveal the coexistence of three coordination species ([TaO₄], [TaO₅], and [TaO₆]) in melts. Their distribution exhibits a regular evolution with increasing Li₂O content: the proportions of five- and six-coordinated Ta-O species gradually decrease, while the four-coordinated Ta-O species increases significantly. This work provides crucial theoretical support for establishing correlations between species with various coordination structures and physical properties in binary Li₂O-Ta₂O₅ melts, as well as for optimizing interfacial dynamics through controlled crystal growth parameters.

The Nd:GYSAG crystal enables multi-wavelength near-infrared laser output, with adjustable wavelengths tailored for specific application requirements, making it highly valuable for space-borne water vapor detection. This study reports, for the first time, the side-pumping characteristics and electro-optical Q-switching performance of this crystal. Using Ø3 × 73 mm and Ø4 × 73 mm crystal rods doped with 1.21 at.% Nd:GYSAG (chemical formula Nd_0.033Gd_0.93Y_1.79Sc_0.70Al_4.54O_11.99), 1060.4 nm laser output was achieved under 808 nm laser diode (LD) side-pumping at a repetition rate of 100 Hz and a pump pulse width of 250 μs. The experimental results show that the Ø4 × 73 mm rod had a higher laser threshold but exhibited significantly superior slope efficiency and maximum output power compared to the Ø3 × 73 mm rod. Using a flat–flat resonator, optimal laser performance was obtained with an output coupler transmission of 35%, yielding a slope efficiency of 37.2%. A maximum output energy of 179.4 mJ was achieved at a pump energy of 646 mJ. Thermal lensing effects were compensated using a flat–convex cavity, leading to improved laser performance and beam quality. Electro-optical Q-switching experiments were conducted using a KD*P crystal. A comparison between voltage-applied and voltage-removed Q-switching techniques revealed superior performance for the voltage-applied method. High-performance laser output was realized, achieving a maximum pulse energy of 59.6 mJ, a pulse width of 14.93 ns, and a peak power of 3.99 MW. This study provides an important foundation for the development of near-infrared laser devices based on Nd:GYSAG.