Birefringence is a key property of optical functional crystals, underpinning their vital applications in angle phase‐matching, polarization control, and various advanced photonic technologies. Currently, TiO 2 exhibits a large birefringence in the visible region, serving as a benchmark material. With the advancement of science and industry, the exploration of new birefringent materials in this wavelength band has become increasingly important. In this work, we proposed a mixed anion strategy to enhance the optical anisotropy, using the Hf‐O‐N system as a case study. Structures with Hf‐O‐N were screened from the NOEMD database for further first‐principles calculations. Six structures with ( E hull ≤ 0.05 eV/atom) possess large bandgaps (1.67–5.02 eV) and significant birefringence (0.17–0.403 @1064 nm). Four structures exhibit potential birefringence in the visible region, I 4/ mmm ‐Hf 2 N 2 O (0.37 @1064 nm), Cm ‐Hf 5 N 6 O (0.219 @1064 nm), C 2/ m ‐Hf 7 N 8 O 2 (0.333 @1064 nm), and Cm ‐Hf 7 N 8 O 2 (0.403 @1064 nm). The birefringence of three of these structures exceeds that of TiO 2 (0.256 @1064 nm). Through structural analysis, we identified that the [Hf 4 NO 2 ], [Hf 4 NO], and [Hf 2 NO 4 ] polyhedra are outstanding optical functional units, which tend to offer significant optical anisotropy. This result offers novel potentialities for the application of birefringent materials and guideline for novel uses of Hafnium oxynitride materials.

Теоретически исследовано распространение излучения волоконного иттербиевого лазера с длиной волны 1,07 мкм в прессованных микропорошках из прозрачных полупроводниковых и диэлектрических материалов (ZnSe, MgF2, CaF2, SiO2, BaF2, MgAl2O4, Al2O3, Nd:Y2O3, YSZ и TiO2), показатели преломления которых находятся в диапазоне 1,38 ¸ 2,48. В результате расчетов установлено, что сочетание рассеяния и интерференции излучения в среде из частиц диаметром порядка микрон приводит к усилению интенсивности излучения в локальных участках среды на один-два порядка по сравнению с интенсивностью падающего излучения. Показано, что с ростом показателя преломления материала частиц это усиление возрастает. По нашему мнению, в подобных локальных максимумах запускаются как нелинейные механизмы поглощения лазерного излучения, приводящие к забросу электронов в зону проводимости, так и процессы ударной ионизации, приводящие к лавинообразному росту концентрации электронов в этой зоне. В результате материал начинает нагреваться вплоть до абляции. Micropowders made of transparent semiconductor and dielectric materials (ZnSe, MgF2, CaF2, SiO2, BaF2, MgAl2O4, Al2O3, Nd:Y2O3, YSZ, and TiO2) are theoretically studied. The refractive indices of these materials are in the range 1.38 ¸ 2.48. As a result of calculations, it is found that the combination of scattering and interference of radiation increases its intensity by one or two orders of magnitude compared to the intensity of the incident radiation in a medium of particles several microns diameter. It is shown that this enhancement increases with the refractive index of the particle material. In our opinion, both nonlinear mechanisms of laser radiation absorption and avalanche ionization lead to an increase in the electron concentration in such local maxima. As a result, the material begins to heat up to the point of ablation.

The melting temperature (Tm) determines the service temperature of ultrahigh-temperature ceramics (UHTCs), so it is of great significance to search for compound with the highest Tm in UHTCs. In present work, the formula to calculate the Tm of UHTCs with the rock salt structure is modified first: Tm = f(c)EVm/(100kB), f(c) = 0.6412*c + 0.9947, which considers the influence of vacancy concentration (c) on the Tm. The calculated Tms are in good agreement with the experimental values of UHTCs, and the calculation accuracy exceeds 91%. The Tm could be obtained by only calculating the elastic modulus and volume per atom. Using this formula, the Tms of ternary HfC-based UHTCs with the rock salt structure are predicted, and a new compound with the highest melting temperature, HfTa2C3, is found. Finally, the empirical relationship between the Tm and shear modulus or Vickers hardness of UHTCs with the rock salt structure is also investigated.

The diagnostic complex is designed to study the dynamic phenomena that occur in the interaction zone between a laser pulse and refractory oxides such as Nd:Y2O3, Fe2O3, ZnSe, and TiO2. This complex includes a compact brightness amplifier that utilizes copper bromide vapors, an optical objective, high-speed cameras (AOS Q-PRI and MegaSpeed-130MK), a digital synchronization system, a 1070 nm ytterbium fiber laser (LS-07N), a focusing lens, a quartz plate, a neutral density filter set, a pin photodiode (SFN2500FA), and a coaxial photocell (FEK-22). The active imaging system has a temporal resolution of 45 mu s. Due to the intense glow of the laser torch resulting from the laser pulse impact on the target, it is not possible to capture images of the interaction zone and the evaporation process using passive filters. However, this issue is resolved by using the small-sized brightness amplifier (with dimensions of l = 38 cm, d = 1.5, V = 67 cm3), which allows for imaging of the droplets formed during the laser torch's presence. Additionally, the surface of the target in the interaction zone is also captured. The characteristics of the melt and the formation of large droplets during the laser pulse impact on the target are determined through this setup.

Finding crystals with high birefringence (Δn), especially in deep-ultraviolet (DUV) regions, is important for developing polarization devices such as optical fiber sensors. Such materials are usually discovered using experimental techniques, which are costly and inefficient for a large-scale screening. Herein, we collected a database of crystal structures and their optical properties and trained atomistic line graph neural network to predict their Δn. To estimate the level of confidence of the trained model on new data, D-optimality criterion was implemented. Using trained graph neural network, we searched for novel materials with high Δn in the Materials Project database and discovered two new DUV birefringent candidates: NaYCO3F2 and SClO2F, with high Δn values of 0.202 and 0.101 at 1064 nm, respectively. Further analysis reveals that strongly anisotropic units with various anions and π-conjugated planar groups are beneficial for high Δn.

Finding birefringent material with giant optical anisotropy is urgent for photonic applications. However, the application of existing birefringent materials is limited by restricted transparency wavelength or optical anisotropy. The process of trial and error is time-consuming and inefficient in terms of resources, especially when compared to the vast design spaces for materials. The immense chemical space necessitates a high-throughput approach for giant optical anisotropy materials design. Here, a full-applied wavelength map of birefringent materials is constructed, from conventional visible expanding to ultraviolet and deep-ultraviolet region by high-throughput screening methods. And highlighted 579 materials birefringence exceeds the one of available commercial birefringent materials in corresponding regions. Significantly, 54 materials possess giant birefringence above 0.5 @1064 nm. Via developing a high-throughput screening technique for microscopic structures with given coordination number, the study further characterizes a comprehensive map of functional modules featuring birefringent activeness. According to the macroscopic and microscopic dual-functional maps, and a novel crystal Li2(HC3N3S3)center dot 5H2O with birefringence difference 0.532 @546 nm is designed and synthesized successfully. This study identifies desired materials with high performance in unheeded chemical spaces. Using high-throughput screening, 579 birefringent materials are identified from the Materials Project database, and a full-applied wavelength map of birefringent materials, along with a map of functional modules, is constructed. image

In this paper we use high-speed video recording in order to study the splashing of melt drops when a Nd:Y2O3 target is exposed to single pulses of ytterbium fiber laser radiation with duration of 1100–4000 μs. The intensity of radiation focused on the target surface into a spot with a diameter of 430 μm was 0.077÷0.46 MW/cm2. Using a “laser monitor” based on CuBr vapor active medium for video recording makes it possible to eliminate the too bright glow of the vapor in the laser plume from the images and to observe the melt splashing directly from the crater. In the experiment, it turns out to be possible to observe the dynamics of the formation of droplets having dimensions of 10–180 μm and constituting 99 % of the mass of all droplets. As a rule, the melt is removed from the crater not in single drops, but rather in the form of jets that are divided into drops only when already in the air. At a radiation intensity of 0.46 MW/cm2, the melt begins to splash 200–250 μs after the start of target evaporation. As the radiation intensity decreases, this delay increases nonlinearly. At a radiation intensity of 0.13 MW/cm2 the melt can no longer splash out of the crater. According to theoretical calculations, splashing is possible if the reactive pressure of the laser plume vapor on the melt pool in the crater exceeds a certain value. Under the conditions of our experiment, the melt can splash out for excess vapor pressure in the crater exceeding 140 kPa.

Nonlinear optical (NLO) materials are significant for their crucial role in the development of modern optoelectronic and laser technology. Recently, fluorooxoborates have aroused the widespread attention for their tight relationship between the micro-properties of functional [BOxF4–x](x+1)– (x = 0, 1, 2, and 3) modules and macroscopic performances. Nevertheless, whether fluorooxoborates with the anionic groups only composed of condensed [BO2F2] units exhibit a strong second harmonic generation (SHG) response remains unclear. Here, eight possible synthetic structures with the [BOF2]∞ chain in the CaB2O2F4 system were predicted by using evolutionary algorithm crystal structure prediction techniques. Among them, CaB2O2F4-I, II, IV, and V are centrosymmetric and CaB2O2F4-III, VI, VII, and VIII are non-centrosymmetric structures. Hence, CaB2O2F4-VI (C2) possesses an extremely short ultraviolet cutoff edge (147 nm) and the largest SHG coefficient among reported non-centrosymmetric fluorooxoborates only consisting of the [BO2F2] group. Also, the origin of the SHG coefficient was analyzed in detail through theoretical calculation.

The high-pressure structures of the Bi-Te system were theoretically predicted by this work, which also clarified some ambiguous structures. Using variable-composition evolutionary algorithms, the crystal structures of the Bi-Te system at high pressures were searched, and one new stable structure BiTe-P-1 was proposed. BiTe-P-1 was discovered to be the experiment's undetected structure by comparing with the experimental XRD. Thereafter, the pressure-composition diagram of the Bi-Te system was calculated using the first-principles method. In contrast to previous reports, Bi2Te3 only had two high-pressure structures, R-3m and C2/m, and it would decompose into BiTe and Te at 13.4 GPa. The calculation of quasi-harmonic approximation shown that the BCC alloy phase of Bi2Te3 only could exist stably under high temperature and high pressure. For BiTe, The phase transition route was P-3m1 -> P-1 -> Pm-3m, and the transition pressure was 7.5 and 11.2 GPa, respectively.

The development of a data-driven science paradigm is greatly revolutionizing the process of materials discovery. Particularly, exploring novel nonlinear optical (NLO) materials with the birefringent phase-matching ability to deep-ultraviolet (UV) region is of vital significance for the field of laser technologies. Herein, a target-driven materials design framework combining high-throughput calculations (HTC), crystal structure prediction, and interpretable machine learning (ML) is proposed to accelerate the discovery of deep-UV NLO materials. Using a dataset generated from HTC, an ML regression model for predicting birefringence is developed for the first time, which exhibits a possibility of achieving fast and accurate prediction. Essentially, crystal structures are adopted as the only known input of this model to establish a close structure-property relationship mapping birefringence. Utilizing the ML-predicted birefringence which can affect the shortest phase-matching wavelength, a full list of potential chemical compositions based on an efficient screening strategy is identified. Further, eight structures with good stability are discovered to show potential applications in the deep-UV region, owing to their promising NLO-related properties. This study provides a new insight into the discovery of NLO materials and this design framework can identify desired materials with high performances in the broad chemical space at a low computational cost.

Using variable-composition crystal structure prediction algorithm USPEX combined with first-principles calculations, we systematically explore stable vanadium hydrides (VxHy) in the pressure range from 0 to 300 GPa. Besides reproducing all previously reported VxHy compounds, we discover three new V-rich (C222-V2H, I4/mmm-V3H2 and C222-V6H5) and three new H-rich (R-3m-V3H7, I-42m-V4H11 and Cmmm-VH11) stable phases. All stable VxHy compounds are metallic, as indicated by their electronic structures. Electron-phonon coupling calculations reveal the potential superconductive nature of VH3 (Fm-3m), VH5 (P6/mmm) and VH11 (Cmmm), with estimated critical temperature of 2.8-4.8 K for VH3, 14.1-21.1 K for VH5 and 61.8-72.6 K for VH11 at 200 GPa, respectively. Superconductivity of VH3 comes largely from coupling of the electrons with V vibrations, while in VH5 and VH11 coupling with H vibrations becomes more important as hydrogen content increases.

Deepultraviolet (UV) nonlinear optical (NLO) materialsare ofintense interest owing to their broad technological applications fromlaser photolithography to semiconductor manufacturing, biomedicine,and attosecond pulse generation. To date, deep UV NLO materials arestill scarce due to the multiple rigorous criteria that should befulfilled. Using evolutionary crystal structure prediction combinedwith first-principles calculations, we systematically explored thepseudobinary Li2O-B2O3 systemand predicted twenty-four metastable structures in the Li2O-B2O3 system. We found that four structuresof LiBO2, e.g., oC16, oP16-1, oP16-2, and mP16, are promisingdeep UV NLO crystals. Among them, oC16-LiBO2, oP16-2-LiBO2, and mP16-LiBO2 exhibit significantly large SHG coefficients(>6 KDP), moderate birefringence (similar to 0.12@1064 nm), and suitableband gaps (similar to 7 eV). Importantly, the oC16-LiBO2 structure is expected to be synthesized experimentally asits formation energy is lower than that of gamma-LiBO2.

Herein, the vacancy‐ordered structures in the ternary Hf–Ta–C system are investigated by the first‐principles method and evolutionary algorithms. In addition to the rocket‐salt structure, two Ta 2 C‐type structures, HfTa 2 C 2 and Hf 2 Ta 2 C 3 , are predicted, and their space groups are determined to be R‐3m . In these two structures, the vacancy layers are formed perpendicular to the c ‐axis, and the vacancies occupy the [Ta 6 ] octahedral interstices. Furthermore, the electronic properties of HfTa 2 C 2 and Hf 2 Ta 2 C 3 , such as the electron‐localization function, density of state, band structure, partial charge density, and charge–density distribution, are calculated and analyzed. It is shown in the results that the localized electrons locate in the layered vacancies originating from the Ta atoms and that they form localized metallic bonds. Therefore, HfTa 2 C 2 and Hf 2 Ta 2 C 3 exhibit higher elastic modulus and Vickers hardness than the rock‐salt structure.

Nonlinear optical (NLO) materials capable of generating coherent light by second harmonic generation (SHG) are urgently needed in modern laser technology. Despite the importance of this class of materials, only a small fraction of non-centrosymmetric (NCS) crystalline compounds with finite electronic band gaps which exhibit SHG response have been studied experimentally or theoretically, and thus an efficient exploration of NLO materials with high performance is greatly limited. In this work, we introduce to date the largest computational NLO materials database which contains calculated SHG coefficients for 2354 NCS crystal structures as well as their electronic band gaps. The computational details and validation of data are presented, along with a detailed description of the database helpful for the usage of these computational results. One of the main features of the present database is that it contains a large number of new thermodynamically stable and metastable structures discovered through evolutionary algorithm searches, providing possibilities for finding novel NLO materials with good properties.

Nonlinear optical (NLO) materials are significant for their crucial role in the development of modern optoelectronic and laser technology. Recently, fluorooxoborates have aroused the widespread attention for their tight relationship between the micro-properties of functional [BOxF4-x]((x+1)-) (x = 0, 1, 2, and 3) modules and macroscopic performances. Nevertheless, whether fluorooxoborates with the anionic groups only composed of condensed [BO2F2] units exhibit a strong second harmonic generation (SHG) response remains unclear. Here, eight possible synthetic structures with the [BOF2](8) chain in the CaB2O2F4 system were predicted by using evolutionary algorithm crystal structure prediction techniques. Among them, CaB2O2F4-I, II, IV, and V are centrosymmetric and CaB2O2F4-III, VI, VII, and VIII are non-centrosymmetric structures. Hence, CaB2O2F4-VI (C2) possesses an extremely short ultraviolet cutoff edge (147 nm) and the largest SHG coefficient among reported non-centrosymmetric fluorooxoborates only consisting of the [BO2F2] group. Also, the origin of the SHG coefficient was analyzed in detail through theoretical calculation.

Traditional infrared (IR) nonlinear optical (NLO) materials such as AgGaS2 are crucial to key devices for solid-state lasers, however, low laser damage thresholds intrinsically hinder their practical application. Here, a robust strategy is proposed for unbiased high-throughput screening of more than 140 000 materials to explore novel IR NLO materials with high thermal conductivity and wide band gap which are crucial to intrinsic laser damage threshold. Via our strategy, 106 compounds with desired band gaps, NLO coefficients and thermal conductivity are screened out, including 8 nitrides, 68 chalcogenides, in which Sr2 SnS4 is synthesized to verify the reliability of our process. Remarkably, thermal conductivity of nitrides is much higher than that of chalcogenides, e.g., 5×AgGaS2 (5.13 W/m K) for ZrZnN2 , indicating that nitrides could be a long-neglected system for IR NLO materials. This strategy provides a powerful tool for searching NLO compounds with high thermal conductivity.

Exploringnew nonlinear optical (NLO) crystals for the output ofdeep-ultraviolet (DUV) lasers via the frequency conversion techniqueis of great interest. Monofluorophosphate is a new chemical systemfor exploring DUV NLO crystals while difluorophosphate is still lackingin research but attracting attention. Herein, difluorophosphate isproved as a new potential member of the DUV NLO materials system basedon high-throughtput crystal structure prediction combined with first-principlescalculations. Our high-throughtput screening identified 34 structuresfor difluorophosphate APO(2)F(2) and monofluorophosphateA(2)PO(3)F (A = Li, Na, K, Rb, Cs) with good thermodynamical(meta)stability and promising NLO properties. Among them, six dynamicallystable APO(2)F(2) structures show DUV performanceas the shortest second harmonic generation (SHG) phase-matching (PM)wavelength around 185-199 nm and SHG coefficient larger thanor comparable to that of KH2PO4 (KDP). Notably,the APO(2)F(2) system possesses enhanced birefringenceand shortened SHG PM wavelength compared to the A(2)PO(3)F system. It reveals that dual-fluorine drives stronger P-Obonding electron density along the direction of n (max) in PO2F2 than that in PO3F, which is responsible for the enhanced birefringence andshortened SHG PM wavelength. These results provide a new directionand insight for exploring DUV NLO crystals.

Weakly agglomerated ZnSe, Cu:ZnSe, and Fe:ZnSe nanopowders have been obtained by evaporating a target of the corresponding chemical composition using an ytterbium-doped fiber laser, generating periodic pulses with a peak power of 600 W and duration of 120 μs. The nanoparticles are shaped as polyhedra and, more rarely, spheres with an average size of 18 nm. The nanopowder production rate at an average laser power of 300 W was ~100 g/h. Calculations showed that initial-target porosity (~30% in our case) leads to scattering of laser radiation and its highly nonuniform distribution in the target. In some regions of the target surface layer 10–15 μm thick, the laser radiation is randomly concentrated, and its intensity, due to the high refractive index of ZnSe (n ≈ 2.48), may exceed the incident radiation intensity by a factor of 10–245. This circumstance facilitates significantly the optical destruction and further evaporation of a target at a low peak incident radiation intensity (~0.43 MW/cm2). Photography of a laser torch showed that target evaporation by periodic laser pulses makes it possible to essentially reduce splashing of melt drops (under certain conditions). The necessary conditions are as follows: the pulse duration should not exceed 400 μs at a peak radiation intensity of 0.21 MW/cm2 and 200 μs at a peak intensity of 0.46 MW/cm2.

A multilevel workflow for designing new photo-voltaic materials based on high-throughput calculations is proposed, which consists of a structure predictor coupled to a property calculator. With the chemical composition as the only input, the workflow will automatically predict structures with theoretically high spectroscopically limited maximum efficiency (SLME). Based on this workflow, 4 thermodynamically stable (one of which is new) and 31 metastable (22 of which are new) non-toxic ABN2 (A = Mg, Ca, Sr, Zn; B = Sn, Ti, Zr) structures with high SLMEs have been discovered. Among these, MgTiN2 (Fd- 3m) and ZnSnN2 (Pna21, Pmc21, and P-4m2) structures are suggested to be promising photovoltaic materials because of their good thermodynamic stability (Ehull < 10 meV per atom), high SLME (>20%), and small carrier effective mass.

Design and exploratory synthesis of new mid‐infrared (mid‐IR) nonlinear optical (NLO) materials are urgently needed for modern laser science and technology because the widely used IR NLO crystals still suffer from their inextricable drawbacks. Herein, a multi‐level data‐driven approach to realize fast and efficient structure prediction for the exploration of promising mid‐IR NLO materials is proposed. Techniques based on machine learning, crystal structure prediction, high‐throughput calculation and screening, database building, and experimental verification are tightly combined for creating pathways from chemical compositions, crystal structures to rational synthesis. Through this data‐driven approach, not only are all known structures successfully predicted but also five thermodynamically stable and 50 metastable new selenides in AIBIIISe2 systems (AI = Li, Na, K, Rb, and Cs; BIII = Al and Ga) are found, among which eight outstanding compounds with wide bandgaps (> 2.70 eV) and large SHG responses (>10 pm V−1) are suggested. Moreover, the predicted compounds I 4¯ 2d‐LiGaSe2 and I4/mcm‐KAlSe2 are successfully obtained experimentally. In particular, LiGaSe2 exhibits a robust SHG response (≈2 × AGS) and long IR absorption edge that can cover two atmospheric windows (3–5, 8–12 µm). Simultaneously, this new research paradigm is also applicative for discovering new materials in other fields.