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Formation of ordered defect structures in lithium niobate crystals of different chemical composition at non-equilibrium processes of different nature
摘要： Ordered defective structures in lithium niobate crystals have been established. The phenomenon is a result of non-equilibrium processes of a different nature: photo-induced light scattering, laser ablation, and creation of cracks during relieving mechanical stresses. The shape of such structures depends on the nature and energy that affect a crystal. A number of concentric areas with a different density of laser-induced defects with a changed refractive index appear during photoinduced light scattering. Concentric clusters of microdomains appear in a macrodomain of another sign at laser ablation as a result of local switching under impulse laser radiation. A number of microcracks with a fractal structure appear near main macro-crack during cracking under mechanical stress. Thus, appearance of ordered defective structure occurs not only in the local spot of direct exposure to laser radiation, mechanical stress, etc., but also in some volume of a crystal around it.
关键词： Doping,Laser ablation,Lithium niobate,Mechanical stress,Defective structure,Photorefractive effect
更新于2025-11-21 11:24:58
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Fano Resonance on Nanostructured Lithium Niobate for Highly Efficient and Tunable Second Harmonic Generation
摘要： Second harmonic generation (SHG) is an important nonlinear process which is critical for applications, such as optical integrated circuit, nonlinear microscopy, laser, etc. Many challenges remain in the improvement of nonlinear conversion ef?ciency, since the typical value is of only 10?5 in nanostructures. Here, we theoretically demonstrate a periodic structure consisting of a lithium niobate (LN) bar and an LN disk, on a nanoscale (~300 nm) thin-?lm platform, which is proposed for a highly ef?cient SHG. By breaking the structure symmetry, a Fano resonance with a high Q, up to 2350 and a strong optical ?eld enhancement reaching forty-two folds is achieved, which yields a high conversion ef?ciency, up to 3.165 × 10?4. In addition to its strong second harmonic (SH) signal, we also demonstrate that by applying only 0.444 V on the planar electrode con?gurations of the nanostructured LN, the wavelength of SH can be tuned within a 1 nm range, while keeping its relatively high conversion ef?ciency. The proposed structure with the high nonlinear conversion ef?ciency can be potentially applied for a single-molecule ?uorescence imaging, high-resolution nonlinear microscopy and active compact optical device.
关键词： harmonic generation and mixing,lithium niobate,Fano resonance
更新于2025-09-23 15:22:29
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Effect of Defects on Spontaneous Polarization in Pure and Doped LiNbO3: First-Principles Calculations
摘要： Numerous studies have indicated that intrinsic defects in lithium niobate (LN) dominate its physical properties. In an Nb-rich environment, the structure that consists of a niobium anti-site with four lithium vacancies is considered the most stable structure. Based on the density functional theory (DFT), the specific configuration of the four lithium vacancies of LN were explored. The results indicated the most stable structure consisted of two lithium vacancies as the first neighbors and the other two as the second nearest neighbors of Nb anti-site in pure LN, and a similar stable structure was found in the doped LN. We found that the defects dipole moment has no direct contribution to the crystal polarization. Spontaneous polarization is more likely due to the lattice distortion of the crystal. This was verified in the defects structure of Mg2+, Sc3+, and Zr4+ doped LN. The conclusion provides a new understanding about the relationship between defect clusters and crystal polarization.
关键词： defects,lithium niobate,dipole moment,spontaneous polarization
更新于2025-09-23 15:22:29
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[IEEE 2018 31st International Vacuum Nanoelectronics Conference (IVNC) - Kyoto, Japan (2018.7.9-2018.7.13)] 2018 31st International Vacuum Nanoelectronics Conference (IVNC) - Investigations on electrical properties and correlations to electron and X-ray energies of pyroelectric LiTaO<inf>3</inf> and LiNbO<inf>3</inf>
摘要： The electrical properties of pyroelectric Lithium Tantalate (LiTaO3) and Lithium Niobate (LiNbO3) were investigated and compared to accessible X-ray energies by using the pyroelectric effect to generate X-rays. The capacitances of different crystals of varying sizes were measured and the resulting permittivities were calculated. A vacuum setup enabled a correlation to the maximum X-ray energies at a variable pressure. The presented results provide an overview of fundamental material properties and the effect on the generated difference of potential.
关键词： Lithium Niobate,pyroelectric crystal,vacuum electron source,X-ray spectrum,permittivity,X-ray energy,electron acceleration,electron emission,capacitance,Lithium Tantalate
更新于2025-09-23 15:21:21
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[IEEE 2018 31st International Vacuum Nanoelectronics Conference (IVNC) - Kyoto, Japan (2018.7.9-2018.7.13)] 2018 31st International Vacuum Nanoelectronics Conference (IVNC) - Self-focusing of electrons emitted by rectangular pyroelectric crystals: A study on geometrical conditions for optimized X-ray intensities
摘要： Pyroelectric crystals such as LiTaO3 or LiNbO3 offer the opportunity to produce X-rays with high energy and intensity. These pyroelectric X-ray sources may be used in XRF applications due to particular advantages. This report deals with systematic studies on the behavior of these crystals enabling an optimization of X-ray intensity. Furthermore, the focusing of electrons emitted by rectangular pyroelectric crystals has been studied.
关键词： Lithium Niobate,pyroelectric crystal,vacuum electron source,X-ray intensity,X-ray spectrum,focusing,electron acceleration,electron emission,Lithium Tantalate
更新于2025-09-23 15:21:21
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Hybrid plasmonica??phononic cavity design for enhanced optomechanical coupling in lithium niobate
摘要： A hybrid plasmonic–phononic cavity design which enables high vacuum coupling rate has been proposed in lithium niobate (LN) phononic crystals (Phncs) that have been perforated by air holes and coated with thin silver film. By tailoring the geometry, optomechanical interaction between the plasmonic modes (produced by the metal/insulator) and the phononic modes (confined by the phononic bandgap effect) is greatly enhanced. Numerical results based on finite-element method (FEM) reveal that in this hybrid plasmonic–phononic design, high vacuum coupling rate that predominantly contributed by moving boundary effect is on the order of 106?Hz, which is about one to two orders higher than that contributed by photoelastic effect shown in conventional phoxonic crystal designs. Results evidence how the vacuum coupling rate depends on geometrical parameters like the radius of the defect air hole, the thickness of silver layer, and LN layer. The simultaneous confinement and strong coupling, combined with other advantages as lack of constraint to the refractive index, and integration of piezoelectric material and metal in a chip, this hybrid design may be suitable for non-invasive biological sensing, optomechanically tunable plasmonic heater for drug release and lab-on-chip devices.
关键词： Optomechanics,Plasmonic-phononic cavity,Vacuum coupling rate,Photoelastic effect,Lithium niobate,Moving boundary effect
更新于2025-09-23 15:21:01
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Integrated electro-optic modulators in x-cut lithium niobate thin film
摘要： Integrated optics is poised to revolutionize several data communication applications. The development of high performance electro-optic modulators is essential for the technology to be viable. In this paper, single-mode electro-optic modulators in x-cut lithium niobate thin film are designed, simulated, and analyzed. The single-mode conditions of lithium niobate ridge waveguides are analyzed in detail. The design parameters of Y-branch and separation distances between electrodes and ridge waveguides are optimized. The half-wave voltage of the electro-optic modulator with device lengths of 10 mm is determined. The half-wave voltage-length product is about 2.2 V·cm, indicating the efficient electric-optical modulation. This study is helpful for understand of electro-optic modulator structures in lithium niobate thin film, as well as for the fabrication of high-performance and multifunctional electro-optic modulation devices.
关键词： Electro-optic modulator,Lithium niobate thin film,Waveguide devices,Integrated optics
更新于2025-09-23 15:21:01
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LiNbO3 integrated system for opto-microfluidic sensing
摘要： In this work, we realized and tested an integrated opto-microfluidics platform entirely made on lithium niobate (LiNbO3) crystals, able to detect the single droplet passage and estimate its size without the need of any imaging processing. It is based on the coupling of a self-aligned integrated optical stage, made of an array of optical waveguides, to a microfluidic circuit such as a T-junction or Cross-junction engraved in the same substrate. The platform presented high quality performances in terms of optical triggering, reproducibility and stability in time, allowing in real-time data analysis. The comparison with standard approaches using microscopes and fast camera imagining acquisition and relative post-processing, showed an increased capability better than 50%. The demonstrated feasibility of integration of these two stages will allow the realization of a Lab-On-a-Chip on a monolithic substrate of lithium niobate, exploiting its multiple applications for manipulation of droplets.
关键词： waveguide,Microfluidic,Droplet,optical trigger,lithium niobate,Lab-on-a-chip
更新于2025-09-23 15:21:01
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Mid-Infrared Electro-Optical Modulation Using Monolithically Integrated Titanium Dioxide on Lithium Niobate Optical Waveguides
摘要： tunable photonic circuits were demonstrated in the mid-infrared (mid-iR) regime using integrated tio2-on-Linbo3 (toL) waveguides. the upper waveguide ridge was made by a sputtered tio2 thin film with broad transparency at λ = 0.4–8 μm and an optimized refractive index n = 2.39. The waveguide substrate is a z-cut single crystalline Linbo3 (LN) wafer that has strong Pockels effect, thus enabling the tunability of the device through electro-optical (e-o) modulation. A sharp waveguide mode was obtained at λ = 2.5 μm without scattering or mode distortion found. The measured E-O coefficient γeff was 5.9 pm/V approaching γ31 of 8.6 pm/V of LN. The ToL waveguide showed a hybrid mode profile where its optical field can be modified by adjusting the TiO2 ridge height. our monolithically integrated ToL modulator is an efficient and small footprint optical switch critical for the development of reconfigurable photonic chips.
关键词： electro-optical modulation,lithium niobate,optical waveguides,mid-infrared,titanium dioxide
更新于2025-09-23 15:19:57
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Enhancement of the second harmonic signal of nonlinear crystals by self-assembled gold nanoparticles
摘要： In second harmonic generation (SHG), the energy of two incoming photons, e.g., from a femtosecond laser, can be combined in one outgoing photon of twice the energy, e.g., by means of a nonlinear crystal. The SHG efficiency, however, is limited. In this work, the harvested signal is maximized by composing a hybrid system consisting of a nonlinear crystal with a dense coverage of plasmonic nanostructures separated by narrow gaps. The method of self-assembled diblock-copolymer-based micellar lithography with subsequent electroless deposition is employed to cover the whole surface of a lithium niobate (LiNbO3) crystal. The interaction of plasmonic nanostructures with light leads to a strong electric near-field in the adjacent crystal. This near-field is harnessed to enhance the near-surface SHG signal from the nonlinear crystal. At the plasmon resonance of the gold nanoparticles, a pronounced enhancement of about 60-fold SHG is observed compared to the bare crystal within the confocal volume of a laser spot.
关键词： gold nanoparticles,nonlinear crystal,second harmonic generation,lithium niobate,plasmonic nanostructures,electroless deposition,self-assembled diblock-copolymer-based micellar lithography,LiNbO3,SHG
更新于2025-09-23 15:19:57