Table of Content

20 October 2025, Volume 54 Issue 10

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Reviews

Progress in Direct Third-Harmonic Generation Based on Third-Order Nonlinear Optical Effect

GUO Xiaotian, LIANG Fei, YU Haohai, ZHANG Huaijin

2025, 54(10):  1671-1686.  doi:10.16553/j.cnki.issn1000-985x.2025.0184

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The third-order nonlinear optical effect is a fundamental phenomenon with extensive applications in laser wavelength extension， modulation， and spectral analysis. Direct third-harmonic generation（THG）， as a typical third-order nonlinear process， can shorten the laser wavelength to 1/3 of the fundamental-wave and triple the photon energy. It enables great optical conversion from infrared light to short wavelengths （e.g.， visible， ultraviolet， and vacuum ultraviolet region）， thus enhancing laser device integration， facilitating high-performance electronic and optical components， and meeting the urgent demands for specific wavelengths in laser processing. Additionally， the inverse process of THG allows optical parametric down-conversion to generate multi-photon entangled states， thus aiding in high-efficiency and multi-dimensional quantum light sources for important applications， such as quantum key distribution and teleportation. Starting from the basic principles of THG， this paper analyzes the strict conditions of energy conservation and momentum conservation for THG process. We summary the development status of THG in bulk nonlinear crystals， topological semimetals， epsilon-near-zero thin films， and silicon-based metasurfaces. In addition， their THG wavelength ranges and conversion efficiencies are also compared in detail. Finally， we discuss the challenges for efficient direct THG in bulk nonlinear crystals and prospect their development trends in the future.

Advancement of Novel Transition Metal Oxyfluoride Nonlinear Optical Crystals

BAI Zhiyong, ZHAO Sangen, LUO Junhua

2025, 54(10):  1687-1695.  doi:10.16553/j.cnki.issn1000-985x.2025.0183

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Nonlinear optical （NLO） crystals， as core components of solid-state lasers， are widely used in advanced fields such as controllable nuclear fusion， quantum communication， and high-precision spectral analysis. Recent studies have shown that oxyfluorides exclusively composed of 4d⁰/5d⁰ transition metal （specifically Zr⁴⁺， Hf⁴⁺， Nb⁵⁺， and Ta⁵⁺） also exhibit wide optical bandgaps with ultraviolet to deep-ultraviolet transparency owing to the increased ionicity of bonds arising from the relatively low electronegativity of Zr⁴⁺， Hf⁴⁺， Nb⁵⁺， and Ta⁵⁺ cations and high electronegativity of fluorine anions. Simultaneously， the polyhedra maintain strong geometric distortion， playing a crucial role in enhancing the NLO effect and birefringence. The optical transmission range of this type of transition metal oxyfluoride can reach the ultraviolet spectral region or even deep ultraviolet spectral region， These properties suggest that the 4d⁰/5d⁰ oxyfluorides are potential ultraviolet NLO candidates. This article presents the latest progress in the design and synthesis of inorganic ultraviolet-transparent NLO crystals based on the oxyfluoride polyhedra of these 4d⁰/5d⁰ transition metals. We summarize eleven relevant NLO crystals， detailing their crystal structures， optical properties （including absorption cutoff edge， optical band gap， second-harmonic generation （SHG）， and birefringence）， and the influence mechanisms of the transition metal oxyfluoride polyhedra on these optical properties.

Research Progress of Magneto-Optical Crystals and Devices

CHEN Wei, WANG Chengqiang, CHEN Yangguo, ZHANG Rui, DANG Yu, CHEN Jiangxu, CHEN Qiuhua, ZHANG Xing

2025, 54(10):  1696-1713.  doi:10.16553/j.cnki.issn1000-985x.2025.0146

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As a key component in laser systems， the core function of magneto-optical isolators relies on the Faraday effect of magneto-optical crystals， which can effectively isolate reflected light and improve the stability of laser systems. This article reviews the development history of magneto-optical materials， focusing on the magneto-optical properties， growth techniques， and application status of rare earth garnet crystals （such as TGG， TAG， TSAG， YIG） and fluoride crystals （such as CeF₃， KTb₃F₁₀）. TGG crystal is currently the most widely used magneto-optical material， but its magneto-optical performance is gradually facing bottlenecks in high-power lasers； TAG and TSAG crystals have better performance， with a Verdet constant more than 30% higher than that of TGG crystal， but they are more difficult to grow； YIG crystal exhibits excellent performance in the mid to far infrared range， with the Verdet constant reaching -515.82 rad/（T·m） at 1 064 nm， but size limitations still need to be overcome. Fluoride crystals （such as CeF₃ and KTF） have emerged as a promising research field due to their high transmittance and low optical absorption. They show great potential， particularly in the ultraviolet （UV） and visible spectral bands， achieving transmittance rates of up to 85% in the UV region. In addition， this article explores the working principle， development history， and research progress of magneto-optical isolators， and looks forward to the application prospects of high-performance magneto-optical materials and devices in the future.

Research Articles

Deuteration-Induced Modulation of Interfacial Polarization in the Memcapacitive Material (CETM)₂[InCl₅(H₂O)]

LU Jiali, LIU Zhaolong, JIN Shifeng, CHEN Xiaolong

2025, 54(10):  1714-1721.  doi:10.16553/j.cnki.issn1000-985x.2025.0164

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Organic-inorganic hybrid memcapacitor material （CETM）₂［InCl₅（H₂O）］ exhibits an exceptionally large interfacial polarization （P_r=31 654 μC/cm²） attributed to proton migration， yet direct experimental evidence for this microscopic mechanism has been lacking. Deuterated analogue （CETM）₂［InCl₅（D₂O）］ was synthesized by heavy-water isotope exchange and the influence of deuteration on crystal structure， phase transitions and electrical properties were systematically investigated. X-ray diffraction and differential scanning calorimetry reveal that the monoclinic Pc structure and the dehydration transition （332 K） remain essentially unchanged after deuteration. Electrical measurements show that deuteration decreases the ionic conductivity from 4.35×10^-7 S/cm to 1.28×10^-7 S/cm and reduces the remnant polarization from 31 654 to 18 811 μC/cm². Density-functional nudged-elastic-band calculations indicate a higher migration barrier for deuterons than for protons， confirming that the polarization attenuation originates from the mass effect and enhanced stability of the deuterium-bonding network. This work provides the first isotope-effect demonstration that interfacial polarization in such hybrids is governed by proton migration， offering a new strategy to tune memcapacitive performance.

Synthesis and Optical Properties of Rb₂CdSi₃Se₈ and K₂HgSi₃S₈ Crystals

CHEN Xinchen, CHE Wangfei, WU Yabo, LI Guangmao, CUI Chen, YANG Zhihua, PAN Shilie

2025, 54(10):  1722-1731.  doi:10.16553/j.cnki.issn1000-985x.2025.0187

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Two new thiosilicate single crystals， Rb₂CdSi₃Se₈ and K₂HgSi₃S₈， were synthesized by spontaneous crystallization from a high-temperature solution under vacuum condition. Both crystallize in the non-centrosymmetric orthorhombic space group P2₁2₁2₁ with layered structures. First-principles calculations of their band structures and optical properties show large birefringence values： 0.167 at 1 064 nm for Rb₂CdSi₃Se₈ and 0.118 at 1 064 nm for K₂HgSi₃S₈. Analyses based on electron localization function （ELF） and response electron distribution anisotropy （REDA） models demonstrate that the optical anisotropy stems from the synergistic interaction between two-dimensional ［CdSi₃Se₈］^2-/［HgSi₃S₈］^2- anionic chains and ［Si₂Q₆］ （Q=Se/S） dimeric units in the layers. Polarizability anisotropy calculations further identified ［Si₂Q₆］ as a critical functional motif responsible for enhancing anisotropy. This work not only presents the successful synthesis of these crystals but also provides novel insights for designing optical crystals with enhanced birefringence. Subsequently， the flux system will be optimized to obtain pure phase powders of the two compounds.

Design of a Continuous-Wave Laser Frequency Doubler Using KBBF Thin-Plate Crystals

WANG Xiaoyang, LIU Lijuan

2025, 54(10):  1732-1739.  doi:10.16553/j.cnki.issn1000-985x.2025.0162

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Deep ultraviolet （DUV） lasers （wavelength is less than 200 nm） play an indispensable role in advanced applications such as lithography， angle-resolved photoemission spectroscopy， and micromachining. For achieving practical and high-precision DUV laser output， the cascade frequency conversion approach based on nonlinear optical crystals has emerged as the most viable solution， whose ultimate performance is determined by the terminal DUV frequency doubling crystal. However， only two DUV nonlinear crystals—KBBF （KBe₂BO₃F₂） and RBBF （RbBe₂BO₃F₂） have been reported to date， both constrained by layered growth habits that yield only millimeter-thick plate-like crystals. To address the technical challenges in fabricating frequency-doubling devices from such thin-plate crystals， conventional solutions employ prism coupling techniques involving optical bonding of two heterogeneous prisms to the crystal surfaces. This approach suffers from inherent limitations： the introduced heterointerfaces not only cause additional optical losses but also become vulnerable points for laser damage， reducing the device's damage threshold by over one order of magnitude compared to the crystal itself. This study innovatively proposes a specialized Brewster-angle cutting method that maximizes the effective optical path length while maintaining phase-matching conditions. By eliminating the prism structures， this prism-free frequency doubler fully exploits the intrinsic high-damage-threshold characteristics of the nonlinear crystal while improving overall transmittance， thereby providing a new pathway for high-power/continuous-wave DUV laser generation.

Multi-Wavelength Laser Operation in Nd∶GdScO₃ Crystal

LIN Wenfang, HUANG Conghui, FANG Qiannan, ZHANG Yuhang, LI Shanming, TAO Siliang, ZHAO Chengchun, HANG Yin

2025, 54(10):  1740-1747.  doi:10.16553/j.cnki.issn1000-985x.2025.171

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We report， for the first time to our knowledge， multi-wavelength laser emission from Nd∶GdScO₃ crystal at ~1 μm and ~1.3 μm. Nd∶GdScO₃ crystal is a novel laser crystal with inhomogeneous broadening spectra， which has great advantages in providing new laser transitions. The Nd∶GdScO₃ crystal was grown by the Czochralski technique in this paper， with Nd³⁺ ions concentration of approximately 0.66% （atomic number fraction）. The laser experiments were conducted using b-cut Nd∶GdScO₃ crystals with dimensions of 5 mm in thickness， a cross-section of 3 mm×3 mm， and two highly polished surfaces without anti-reflective coatings. Multi-wavelength lasers were demonstrated by a single intracavity quartz birefringent plate （QBP）. The QBP featured a thickness of 2 mm， an optical axis aligned along its surface， and no additional coatings applied. The experimental setup incorporated a simple V-fold resonator cavity designed to mitigate thermal effects， within the QBP at Brewster’s angle in the cavity. Simulations on tunable lasers mechanism were performed as well， to evaluate the performance of QBP plate in this system. At 1 μm region， an efficient continuous wave （CW） laser at 1085.0 nm attained an output power up to 5.3 W with slope efficiency of 61.0% in free running mode. Additionally， maximum output power of 3.5 and 2.3 W was achieved at 1 071.4 and 1 092.6 nm， with slope efficiencies of approximately 45.0% and 30.0%， respectively. At 1.3 μm region， an efficient dual-wavelength CW laser at 1 353.6 and 1 375.3 nm reached an output power up to 1.25 W with slope efficiency of 39.0% in free running mode. Furthermore， lasers with a tunable range of 4.0 nm at approximately 1 375.3 nm were also obtained. Our results indicate that Nd∶GdScO₃ is capable of producing efficient multiple lasers at 1 071.4， 1085.4， 1092.6， 1353.6 and 1375.3 nm， expanding laser wavelength of Nd³⁺ ion.

Gauss Quadrature Calculation of Bessel Functions with High Precision

WANG Xiaomei, ZHANG Qingli

2025, 54(10):  1748-1763.  doi:10.16553/j.cnki.issn1000-985x.2025.0170

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Bessel functions are essential for studying wave propagation， heat conduction， and related fields. It is important to compute them with high precision in engineering sciences. A method to calculate Bessel functions J_ν （z）， Y_ν （z）， I_ν （z） and K_ν （z） using Gaussian quadrature is presented. By partitioning integral interval into subintervals with the zeros of sine and cosine functions and quadrature was applied on subintervals， the effect of trigonometric oscillations on integral precision can be effectively suppressed. The integral over ［0， ∞］ for Bessel integral representation is decomposed into integral over ［0， T］ and ［T， ∞］， where trigonometric function oscillations are explicitly handled within ［0， T］ through further partitioning integral intervals with trigonometric function zeros， on subintervals Gauss-Legendre quadrates were applied to obtain high precision quadrature computation. Meanwhile， when the real part of z is small in magnitude， the integration interval ［0， T］ should be appropriately extended to ensure that the Gauss-Legendre quadrature component contributes dominantly to the numerical result， which is very useful to improve calculation precision. Due to exponential decay properties of integrand， the ratio of Gauss-Laguerre on ［T， ∞］ would be very little， which would be very useful to improve numerical compute precision. The Gaussian quadrature implementation for Bessel functions isprogrammatically validated with Delphi code， yielding results exhibits remarkable agreement with Mathematica's built-in functions. It is unnecessary for this method to consider series convergence and recurrence procedures， and can be used to calculate Bessel functions with arbitrary orders and complex variable on entire complex plane， which has broad versatility and generality.

First-Principles Study on Electro-Optic Effect of Germanium-Based Metal Halide Perovskites

SHI Xuemei, YANG Guangsai, YE Ning

2025, 54(10):  1764-1771.  doi:10.16553/j.cnki.issn1000-985x.2025.0194

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With the growing demand and rapid development of optical modulators， the research and exploration of electro-optic crystals are of great significance. However， the available types of electro-optic crystals are limited， making the search for new candidates an urgent task. In this work， we employed first-principles calculations using the ABINIT package， based on density functional perturbation theory and the 2n+1 theorem， to investigate three ABO₃-type perovskite crystals of interest for green energy applications， namely CsGeX₃ （X=Cl， Br， and I）. By analyzing both the electronic and ionic contributions to the electro-optic coefficients， it is found that the dominant contribution originates from ionic displacements， particularly the stretching vibrations between Ge and halogen atoms. These vibrations strongly influence the polarization of the distorted octahedra， thereby enhancing the electro-optic response of the crystals. Notably， our calculations show that the electro-optic coefficient of CsGeI₃ with space group R3m reaches -30.51 pm/V， comparable to that of the benchmark electro-optic crystal lithium niobate， highlighting CsGeI₃ as a promising candidate for future electro-optic applications.

NaCeF(SO₄)₂: Synthesis Structure of New Cerium Fluoride Sulfate and Its Nonlinear Optical Property

LU Xinyi, WANG Ruixi, LI Mengyue, WU Liming, CHEN Ling

2025, 54(10):  1772-1779.  doi:10.16553/j.cnki.issn1000-985x.2025.0152

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A new sodium cerium （Ⅳ） fluoride sulfate， NaCeF（SO₄）₂， was synthesized by hydrothermal method. Single crystal X-ray diffraction data reveal that it crystallizes in noncentrosymmetric orthorhombic space group P2₁2₁2₁ （No.19）， with unit cell parameters of a=8.233 0（2） ?， b=8.591 0（2） ?， c=9.261 1（2） ?， α=β=γ=90°， V=655.03（3） ?³， Z=4. The three-dimensional framework consists of interpenetrating Ce—F—O polyhedral chains and Na—O polyhedral chains that are formed by F-corner-sharing ［CeO₇F₂］ polyhedra and edge-sharing ［NaO₈］ polyhedra， respectively. Within such a framework， the interstitial sites are occupied by isolated （SO₄） tetrahedron. The band gap was measured to be of approximately 2.70 eV. The powder second-harmonic generation （SHG） response was measured to be approximately twice that of the reference material KH₂PO₄. In contrast to the centrosymmetric parent compound Ce（SO₄）₂， the incorporation of fluorine as a secondary ligand triggers structural distortion， leading to the formation of noncentrosymmetric NaCeF（SO₄）₂. First-principles calculations analyses reveal that the band gap is primarily determined by the Ce-4f， O-2p， S-3p and F-2p crystal orbitals， and the optical properties are mainly governed by ［CeO₇F₂］ polyhedron with minor contribution of （SO₄） tetrahedron. The nonzero independent 2nd-order nonlinear optical coefficients are calculated to be d₁₄=d₂₅=d₃₆=-2.672 pm/V.

Growth, Spectral and Laser Performance of Yb³⁺ Doped Ca(Y, Gd)AlO₄ Mixed Crystals

WU Wenjie, TAN Juncheng, ZHANG Yaxin, LI Zhen, LYU Qitao, ZHANG Peixiong, CHEN Zhenqiang

2025, 54(10):  1780-1786.  doi:10.16553/j.cnki.issn1000-985x.2025.0169

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Structurally disordered crystals exhibit non-uniform spectral broadening due to diverse local environments， attracting significant attention for their potential applications in ultrafast lasers. Yb∶CaY_0.8Gd_0.2AlO₄ （CYGA） crystals with a 10% （atomic fraction） Yb³⁺ doping concentration were grown by Czochralski method. The polarization optical properties and laser characteristics of Yb∶CYGA crystals were studied. The polarization absorption spectra， polarization emission spectra， and fluorescence decay curves of the crystal samples at room temperature were tested. Due to the strong disorder in the CYGA mixed crystals， the spectra of Yb∶CYGA crystals show non-uniform broadening， with the half-width of the absorption spectrum reaching 25.0 nm and the full width at half maximum of the emission spectrum reaching 92.2 nm in the π polarization direction. Additionally， at a high doping concentration of 10%， the fluorescence lifetime is as long as 1.04 ms. Continuous and stable laser outputs of approximately 1.05 μm are achieved in both the short cavity and V cavity. The maximum laser output power in the short cavity is 4.400 W， while the V cavity achieve tunable laser output with a tuning range of 23 nm using a birefringent filter （BF）.

Crystal PbMg₆Ga₆S₁₆: Synthesis and Study of Nonlinear Optical Properties

LI Junzhe, LIU Binwen, GUO Guocong

2025, 54(10):  1787-1795.  doi:10.16553/j.cnki.issn1000-985x.2025.0143

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Nonlinear optical （NLO） crystals have garnered extensive attention due to their frequency conversion capabilities in laser systems. In this study， a novel NLO crystal， PbMg₆Ga₆S₁₆， was successfully synthesized by introducing alkaline earth metal cations （Mg²⁺） and polyhedral structural units with lone pair electrons （Pb²⁺） into the gallium-based chalcogenide system using the high-temperature solid-state method. Structurally， this crystal crystallizes in the non-centrosymmetric P-6 space group， with its crystal structure characterized by Pb²⁺ occupying the interstitial sites of the three-dimensional ［Mg-Ga-S］_∞ framework. In terms of optical properties， it exhibits a phase-matchable second-harmonic generation （SHG） response under 1 910 nm laser irradiation， with a SHG intensity of 0.1 times that of AgGaS₂ and an experimental optical bandgap of 2.85 eV. Theoretical calculations based on first-principles demonstrate that PbMg₆Ga₆S₁₆ is an indirect bandgap semiconductor. Electrons transition from point G in the Brillouin zone to a region between points H and K， with a theoretical bandgap of 2.55 eV. This work demonstrates that the SHG response mainly originates from the synergistic effect of the ［GaS₄］ tetrahedral and ［PbS₆］ polyhedral structural units.

Er³⁺/Yb³⁺ Codoped ScLuSi₂O₇ Mixed Crystals: Construction and Performance Investigation of High-Performance 1.55 μm Laser Crystals

GONG Xinghong, CHEN Yujin, HUANG Jianhua, LIN Yanfu, HUANG Yidong

2025, 54(10):  1796-1810.  doi:10.16553/j.cnki.issn1000-985x.2025.0167

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Eye-safe 1.55 μm lasers have significant applications in optical communication， LiDAR， and other fields. This study combines theoretical modeling with experiments to explore the properties of 1.55 μm laser crystals. The optical， mechanical， and thermal characteristics of ScLuSi₂O₇ crystals were simulated theoretically， uncovering the link between their structure and performance. The refractive index temperature coefficient of ScLuSi₂O₇ was calculated as 4.11×10^-6 K^-1. The elastic stiffness coefficients were also determined， and using the Voigt-Reuss-Hill approximation， key thermodynamic properties were derived： Debye temperature （~554 K）， specific heat capacity （0.61 J·g^-1·K^-1 at 300 K）， and average thermal conductivity （8.6 W·m^-1·K^-1 at 300 K）. Experimentally， Er∶Yb∶ScLuSi₂O₇ single crystals were grown via the Czochralski method， and their spectroscopic properties as 1.55 μm laser gain media were examined. End-pumped by a 975.4 nm laser diode， a continuous 1.55 μm laser output of up to 1.06 W with a slope efficiency of 13.53% was achieved. This work offers valuable theoretical and experimental insights for developing 1.55 μm laser crystals.

Potassium Molybdenum Tellurite Crystals: Design, Synthesis, and Second-Order Nonlinear Optical Properties

KONG Fang, HE Tiantian, MAO Jianggao

2025, 54(10):  1811-1822.  doi:10.16553/j.cnki.issn1000-985x.2025.0157

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New potassium molybdenum tellurite nonlinear optical crystal， K₆H₄（Mo₃Te₄O₁₈）₂（MoO₆）（H₂O） （KMTO） was synthesized by hydrothermal method. KMTO crystallizes in the polar P3 space group and is built from ［Mo₃Te₄O₁₈］ two-dimensional layers that are separated by distorted MoO₆ octahedra， K⁺ and lattice water. The compound exhibits a phase-matchable second-harmonic generation （SHG） intensity about three times that of KDP. Variable-temperature single-crystal X-ray diffraction， high-precision DSC and temperature-dependent SHG measurements reveal that KMTO undergoes single-crystal to single-crystal transition at approximately 176 ℃. During the phase transition， their basic framework have not significantly changed， but their structural symmetry have undergone a fundamental transformation and the space group changes from polar P3 to centrosymmetric P-3， resulting in loss of SHG activity. When the larger Cs⁺ is substituted for K⁺， increased steric hindrance between adjacent layers forces the MoO₆ octahedra to be completely removed， yielding Cs₂（Mo₃Te₄O₁₈）（H₂O） （P-1）. Notably， all three structures （P3， P-3 and P-1） share the similar ［Mo₃Te₄O₁₈］ two-dimensional layers； the macroscopic symmetry is dictated by the symmetry of the interlayer species. This work not only presents the first potassium molybdenum tellurite nonlinear optical material but also provides a comprehensive view of structure-property relationships through multiple in situ characterizations， offering experimental guidance for the rational design of new second-order NLO crystals.

Simulation of Phase Transition and Stress Evolution in Laser-Irradiated KDP Crystals: Analysis of Damage Mechanisms

DONG Haoming, FU Weiling, CHENG Xiyue, DENG Shuiquan

2025, 54(10):  1823-1835.  doi:10.16553/j.cnki.issn1000-985x.2025.0166

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This study systematically investigates the relationship between laser-induced bulk damage and the tetragonal-monoclinic phase transition in potassium dihydrogen phosphate （KDP） crystals. Through thermo-mechanical coupling simulations， the temperature and stress field distributions under laser irradiation were quantitatively analyzed. The results reveal that the peak temperature at the laser irradiation center significantly exceeds the critical phase transition temperature， while the laser-induced thermal stress remains below the threshold required for plastic deformation or structural damage. Phase-field simulations demonstrate that stress concentration occurs at phase boundaries during the tetragonal-monoclinic transition， surpassing the yield strength of KDP and initiating plastic deformation. Notably， the simulated high-stress regions exhibit remarkable consistency with the experimentally observed cross-shaped crack morphology. Further analysis indicates that as temperature increases or displacement constraints weaken， phase transition-induced stress can exceed both the yield strength and fracture limit， directly triggering crack formation. These findings confirm that high stress concentration caused by the tetragonal-monoclinic phase transition is the key factor in the formation of characteristic cross-shaped damage in KDP crystals， providing new theoretical insights into their laser damage mechanisms.

Growth, Spectroscopic Properties, and Femtosecond Laser Performance of Yb³⁺∶Ca₃Li_0.275Nb_1.775Ga_2.95O₁₂ Crystals

LI Xuhong, ZHU Zhaojie, HUANG Yizhi, TU Chaoyang, WANG Yan

2025, 54(10):  1836-1843.  doi:10.16553/j.cnki.issn1000-985x.2025.0158

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Yb³⁺∶Ca₃Li_0.275Nb_1.775Ga_2.95O₁₂ （Yb³⁺∶CLNGG） laser crystals with various doping concentrations were successfully grown using the Czochralski method， and their structural， spectroscopic， and laser properties were systematically investigated. X-ray diffraction results indicate that the diffraction peaks of all samples matched well with the standard garnet pattern， with no secondary phases observed. Spectral analysis confirmed that Yb³⁺∶CLNGG crystals exhibit broadband transitions in the near-infrared region. Specifically， the 10%Yb³⁺∶CLNGG crystal shows a full width at half maximum （FWHM） of 37 nm for absorption and 40 nm for emission， and 5%Yb³⁺∶CLNGG crystal shows a maximum emission cross-section of 1.398×10^-20 cm². Low-temperature emission spectra exhibits multiple Stark-split peaks， indicating that the Yb³⁺ occupy non-equivalent and structurally disordere local environments， with their luminescence behavior characterized by cooperative interactions. The fluorescence lifetime increase with Yb³⁺ concentration， exceeding 1 ms at room temperature for the 10% doped crystal. The 10%Yb³⁺∶CLNGG crystal enabled a stable femtosecond laser output with a central wavelength of 1 058 nm， pulse duration of 67 fs， spectral bandwidth of 17.7 nm， average power of 35 mW， and a peak power of approximately 6.87 kW. These results demonstrate excellent mode-locking stability and broadband gain characteristics. Overall， the spectroscopic and laser performance data highlight the great potential of Yb³⁺∶CLNGG crystals as promising gain media for ultrafast and tunable broadband lasers.

Growth and Performance of Triangular Symmetric of High-Temperature Phase Barium Borate Crystal

HUANG Yisheng, LIU Lehui, ZHANG Lizhen, LIN Zhoubin, LUO Xingmu, CHEN Wei

2025, 54(10):  1844-1848.  doi:10.16553/j.cnki.issn1000-985x.2025.0153

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The high-temperature phase α-BBO crystal is an ideal ultraviolet birefringent crystal， but residual stresses caused by phase transitions during its growth process can easily lead to cracking during machining. This paper reports the growth and optical properties of α-BBO crystals. The α-BBO crystals up to ?80 mm×50 mm with transparency and free inclusion were grown by Czochralski method， guided by the theory of crystal morphology and habits. The α-BBO crystal exhibits triangular symmetry， with the c-axis being surrounded by the trigonal pyramids ｛1102｝ and hexagonal prisms ｛1120｝ of the α phase. The crystal faces of α-BBO crystal can keep the α phase stable at room temperature and solve the problem of cracking of α-BBO crystals. Moreover， the existence of crystal faces can greatly eliminate the residual thermal stress in the crystal. The results show that the grown α-BBO crystals have high transmittance in the range from 200 nm to 2 200 nm and excellent quality， which has important application in ultraviolet high power polarized laser devices.

Spectroscopic Gain Bandwidth Modulation and Laser Performance of Ytterbium-Doped Mixed Crystals

LIN Ke, ZHANG Yaxin, WU Wenjie, LI Lin, LIN Changlang, ZENG Huangjun, NIE Haiyu, LI Zhiqiang, ZHANG Ge, LI Zhen, ZHANG Peixiong, CHEN Weidong, CHEN Zhenqiang

2025, 54(10):  1849-1857.  doi:10.16553/j.cnki.issn1000-985x.2025.0172

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Ultrashort lasers have attracted considerable attention due to their extensive applications in precision micromachining and biomedicine， and their development strongly relies on laser gain media with broad gain bandwidths. Compared with laser glass， rare-earth-ion-doped disordered crystals combine broad emission bandwidths with excellent thermal and mechanical stability， making them ideal candidates for generating ultrafast laser pulses. However， a systematic understanding of the mixed composition， crystal structure， and their structure-property relationships regarding emission bandwidth and central ligand symmetry remains lacking. In this work， several mixed crystal systems were systematically investigated， including Yb∶Y₂（Ca，Mg）₃（SiO₄）₃， Yb∶Ca（Y，Gd）AlO₄（Yb∶CALYGO） and Yb∶（Gd，Y）AlO₃（Yb∶GYAP）， and reveal the intrinsic correlations between the mixed composition， structural disorder， and the spectral gain bandwidth of Yb³⁺. Guided by these theories， Yb∶CALYGO and Yb∶GYAP single crystals were successfully grown， enabling the generation of ultrafast pulses with durations of 25 and 23 fs， respectively. This work provides a theoretical foundation and an effective approach for the rational design and performance optimization of disordered crystals for ultrafast laser applications.

Growth Process of Large-Sized Yb∶CALGO Crystal

LIU Xiaohu, ZHU Zhaojie, TU Chaoyang, WANG Yan

2025, 54(10):  1858-1866.  doi:10.16553/j.cnki.issn1000-985x.2025.0139

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The growth process of large-sized Yb∶CALGO crystals using the Czochralski method was explored and analyzed in terms of solid-phase reaction temperature， crystal rotation rate， growth rate， and cooling rate. XRD patterns of polycrystalline materials after sintering reaction at different temperatures were compared， and it was found that the raw materials could react completely at 1 350 ℃. The crystal rotation rate and pulling rate were optimized based on the cracked cross-section and surface smoothness of the as-grown crystals. The cause of cracks due to the cooling rate was analyzed by temperature-variable Raman spectroscopy. Stress distribution maps of different crystal planes obtained with different cooling rates were studied. It was concluded that for Yb∶CALGO crystals grown along c-axis， a high cooling rate is more likely to cause thermal stress accumulation on the （001）plane， which is the major cause of cracks during crystal growth. After optimizing the growth process with several methods， stable growth of ?50 mm×110 mm Yb∶CALGO crystals has been achieved. These crystals have low scattering loss （0.001 796 cm^-1） and high optical homogeneity （4.21×10^-5）， can be machined into various sizes and shapes， and provide a basis for the preparation of Yb∶CALGO slab and ultrafast lasers.