Growth, microstructure and optical characteristics of doped LiNbO3:Gd and LiNbO3:Cu:Gd lithium niobate crystals

A compositionally homogeneous nonlinear optical single crystal of double-doped LiNbO3:Gd3+(0.003):Mg2+(0.65 wt.%) was obtained. Fine features of the LiNbO3:Gd3+(0.003):Mg2+(0.65 wt.%) crystal structure were studied from the Raman spectra of the first and second orders upon excitation by laser lines in the visible (532 nm) and near-IR (785 nm) regions. When the Raman spectrum was excited by a 785 nm laser line in the frequency range of 1000–2000 cm−1 for the first time, a number of low-intensity lines in the range of 900–2000 cm−1, corresponding to the second-order Raman spectrum, were discovered. The same lines also appear in the spectrum upon excitation by a laser line with a wavelength of 532 nm, but their intensities are significantly (by an order of magnitude or more) lower. It is shown that in the structure of the double-doped LiNbO3:Gd3+(0.003):Mg2+(0.65 wt.%), the crystal oxygen-octahedral clusters MeO6 (Me–Li, Nb, Gd, Mg) are slightly distorted, and in addition, the value R = [Li]/[Nb] ≈ 1 is close to that for a nominally pure stoichiometric crystal.

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Investigation of the Structural Perfection of a LiNbO3:Gd3+(0.003):Mg2+(0.65 wt.%) Double-Doped Single Crystal Using the Raman Spectra Excited by Laser Lines in the Visible (532 nm) and Near-IR (785 nm) Regions

Lithium niobate (LN) is a type of multifunctional dielectric and ferroelectric crystal that is widely used in acoustic, optical, and optoelectronic devices. The performance of pure and doped LN strongly depends on various factors, including its composition, microstructure, defects, domain, and homogeneity. The structure and composition homogeneity can affect both the chemical and physical properties of LN crystals, including their density, Curie temperature, refractive index, and piezoelectric and mechanical properties. In terms of practical demands, both the composition and microstructure characterizations these crystals must range from the nanometer scale up to the millimeter and wafer scales. Therefore, LN crystals require different characterization technologies when verifying their quality for various device applications. Optical, electrical, and acoustic technologies have been developed, including x-ray diffraction, Raman spectroscopy, electron microscopy, and interferometry. To obtain detailed structural information, advanced sub-nanometer technologies are required. For general industrial demands, fast and non-destructive technologies are preferable. This review outlines the advanced methods used to characterize both the composition and homogeneity of LN melts and crystals from the micro- to wafer scale. 

Omni‐functional crystal: Advanced methods to characterize the composition and homogeneity of lithium niobate melts and crystals

The theoretical effects of biaxial strain on the structural, electronic, optical, and thermoelectric properties of LiNbO3 were investigated using the Wien2k and BoltzTraP programs with the GGA approximation. The lattice thermal conductivity was calculated by the GIBBS code. We demonstrate that the bandgap value decreases and increase with the tensile and compressive strain respectively. The optical absorption and the optical conductivity of LiNbO3 can be enhanced by applying tensile biaxial strain. The thermoelectric properties are also investigated. LiNbO3 pure and under the biaxial strain is a p-type material. Our compounds are promising candidates for thermoelectric applications. 

Effect of biaxial strain on structural, electronic, optical and thermoelectric properties of LiNbO3: Ab-initio calculations

Third-Order Nonlinear Characteristics and the Temperature-Dependent Refractive Index of Sm/Tm: YCa4O(BO3)3 for Use in Quasi-Parametric Chirped Pulse Amplification

Praseodymium ion (0.5, 1 mol%) and magnesium ion (1, 5 and 7 mol%) co-doped LiNbO3 crystals have been grown by Bridgman method. The crystal was designed to absorb idler generated by the quasi parametric chirped pulse amplification (QPCPA) system near 1588 nm (the pump is 1064 nm and signal is 3200 nm). The contents of Praseodymium (Pr) and magnesium (Mg) ions in the crystals were measured, and the crystal structure and Raman vibration mode were characterized. The optical properties of the crystal were systematically investigated, the transmittance of the crystal at 3200 nm and 1064 nm was about 75%, and there is an obvious absorption band at 1588 nm. The thermal properties of the crystal were studied, and the results showed that the thermal properties of the crystal were improved by doping Mg2+. The laser damage threshold of Pr3+(0.5mol%)-Mg2+(7mol%) co-doped LiNbO3 crystal was as high as 109.73 × 107 W/cm2 (@1064 nm, 5 ns).

Growth and optical properties of Pr-Mg co-doped LiNbO3 crystal using Bridgman method

Laser cavitation degradation is a new technology for dye wastewater treatment. By designing and building a laser cavitation experimental platform, the acid black water solution was degraded by laser cavitation under different operating conditions, and the degraded solution was analyzed and characterized by ultraviolet spectrophotometer to obtain the influence of laser energy and initial concentration of the solution on the degradation ability. The generation process of hydroxyl radical was summarized through the study of laser-induced cavitation bubble pulsation, and the degradation mechanism of acid black was further revealed. The results show that with the increase of laser energy, the degradation rate of acid black solution with initial concentration of 20 mg/L gradually increases from 0.78% to 27.28%. When the laser energy of is 100 mJ, the solution with the initial concentration of acid black in the range of 5–20 mg/L is selected, and the degradation rate decreases from 98.55% to 7.63%. The higher the laser energy is, the greater the degradation rate is. However, if the initial concentration is higher, it is difficult to degrade the acid black solution by laser cavitation. 

Ao Liu

Papers

Growth and optical properties of Pr-Mg co-doped LiNbO3 crystal using Bridgman method

Study on pulsation characteristics of laser-induced cavitation bubble and its degradation of acid black solution