光学参量振荡器的相位匹配

基于非线性昌体的相位匹配理论，计算了比较典型晶体的调谐曲线，并且详细分析比较了各类光学参量振荡器的相位匹配过程，对周期性极化铌酸锂的准相位匹配理论进行了全面的论述。     

基于非线性光学差频及参量效应的太赫兹源

基于非线性光学技术的THz源具有其独特的性能和优点,将基于非线性光学差频原理和光学参量效应,从理论上研究并分析THz波与抽运光、闲频光及相位匹配角之间的关系,得到THz波输出的条件和范围,并设计出宽波段连续可调的THz源。以调QNd∶YAG激光器和光学参量振荡器(OPO)作为抽运源,以GaSe和MgO∶LiNbO3晶体作为差频非线性晶体,根据相位匹配理论及光学参量效应,搭建两套THz波产生系统。其中,基于光学参量效应的THz辐射源有效地产生出THz信号。     

脉宽可调光学参量振荡器的研究

利用振 放双池受激布里渊散射 (SBS)脉宽可调激光系统抽运非临界相位匹配KTP光学参量振荡器(OPO) ,在脉宽从小于 1ns至 6ns之间变化。小能量抽运的情况下 ,实现了OPO低阈值、较高转换效率运转 ,获得了脉宽可调参量激光 ,并且根据长脉冲抽运光学参量振荡器特点 ,结合实验结果对光学参量振荡器的输出特性进行了分析。     

中红外内腔式单谐振光学参量振荡器的研究进展

中红外全固态光学参量振荡器,由于宽的调谐范围、低阈值、高效率、高重复率及小型化的优点,在光电对抗、激光雷达、激光测距、光谱测量以及在环境监测等领域都有广泛的应用前景。全固态中红外激光器一直是激光技术研究的热点。本文重点介绍了基于双折射相位匹配晶体（如KTA、KTP）和准相位匹配晶体（如PPKTP、PPKTA、PPLN）的中红外内腔单谐振（ISRO）光学参量振荡器的一些最新的研究进展,并对其发展趋势进行了展望。     

准相位匹配光参量振荡器理论研究与优化设计

研究了准相位匹配条件下光学参量振荡理论,对单谐振情况下参量增益同极化反转周期的关系进了讨论;从理论上详细地分析了准相位匹配参量振荡器中谐振腔长度、晶体长度、抽运光脉宽以及信号光输出透过率对建立振荡所需泵浦光能量阈值大小的影响,并通过实验验证了理论分析的适用性.     

1064nm泵浦温度调谐PPLN光学参量振荡器

对脉冲泵浦的温度可调准相位匹配(QPM)光学参量振荡器(OPO)进行了研究.LD泵浦的声光调Q Nd:YAG激光器输出的1064nm脉冲激光做泵浦源,极化周期为30.7μm的单周期PPLN做光学参量振荡器的参量晶体,通过控制参量晶体的温度可以得到信号光的波长调谐输出.在LD电流17A得到信号光的平均功率最大为230mW,转化效率达13%.     

掺镁铌酸锂微结构多周期调谐光学参量振荡器

从傅里叶展开三波耦合波方程出发，对准相位匹配光学参量振荡进行了初步的理论分析，同时对准相位匹配周期极化掺镁铌酸锂微结构光学参量振荡进行了实验研究。通过改变微结构周期，实现了信号光从1.45~1.72 μm的输出，最小阈值为30 μJ。在温度30 ℃，抽运功率为300 mW，最大信号光输出功率为56 mW，斜率效率达18.7%。由于掺镁铌酸锂微结构抗光损伤性能显著提高，无需在高温下进行运转，使得掺镁铌酸锂微结构光学参量振荡器在常温条件下实现连续运转成为可能。与同成份铌酸锂微结构参量振荡器相比，结构更加紧凑，易于实现小型化。     

振荡技术与振荡器、谐振回路

0322472约瑟夫森阵列振荡器的相位锁定分析[刊]/高斌//电波科学学报.—2003,18(3).—275～280(L)0322473X~(2K+1)型振荡器的量纲分析[刊]/黄小莉//四川工业学院学报.—2003,22(1).—22～23,27(E)0322474利用光参量振荡器测量腔内增强吸收光谱[刊]/李少成//光电子.激光.—2003,14(5).—534～537(C)0322475温度调谐准相位匹配光学参量振荡器[刊]/臧贵艳//光电子.激光.—2003,14(5).—469～472(C)     

近非临界相位匹配温度调谐MgO：LiNbO3OPO

通过对MgO:LiNbO3参量过程温度相位匹配及走离角，允许参量等运转参数的理论计算与分析，确定了晶体的切割角度θ=82℃，以近非临界相位匹配（NCPM）取代NCPM，将温度调节范围控制在较低的温度上，研制了532nm泵浦的MgO:LiNbO3温度调谐脉冲光学参数振荡器（OPO），在800～1700nm波段实现连续调谐输出。参量泵浦功率密度阈值为57.3MW/cm^2，泵浦能量约2倍阈值处，单谐振（SRO）参量转换效率为11%以上。     

内腔式KTP OPO发散角的实验研究

实验研究了非临界相位匹配 (NCPM)的内腔式KTP光学参量振荡器 (OPO)的光束发散角与OPO谐振腔参数的关系。证明了望远镜型共焦非稳谐振腔是压缩OPO光束发散角的有效方法。     

Compositional and Dimensional Control of 2D and Quasi‐2D Lead Halide Perovskites in Water

Blue light emitting two dimensional (2D) and quasi‐2D layered halide perovskites (LHPs) are gaining attention in solid‐state lighting applications but their fragile stability in humid condition is one of the most pressing issues for their practical applications. Though water is much greener and cost effective, organic solvents must be used during synthesis as well as the device fabrication process for these LHPs due to their water‐sensitivity/instability and consequently, water‐stable blue‐light emitting 2D and quasi‐2D LHPs have not been documented yet. Here, water‐mediated facile and cost‐effective syntheses, characterizations, and optical properties of 16 organic–inorganic hybrid compounds are reported including 2D (A′)₂PbX₄ (A′ = butylammonium, X = Cl/Br/I) (8 compounds), 3D perovskites (4), and quasi‐2D (A′)_pA_x?1B_xX_3x+1 LHPs (A = methylammonium) (4) in water. Here, both composition and dimension of LHPs are tuned in water, which has never been explored yet. Furthermore, the dual emissive nature is observed in quasi‐2D perovskites, where the intensity of two photoluminescence (PL) peaks are governed by 2D and 3D inorganic layers. The Pb(OH)₂‐coated 2D and quasi‐2D perovskites are highly stable in water even after several months. In addition, single particle imaging is performed to correlate structural–optical property of these LHPs.     

Orientation Regulation of Tin‐Based Reduced‐Dimensional Perovskites for Highly Efficient and Stable Photovoltaics

Tin‐based perovskites have exhibited high potential for efficient photovoltaics application due to their outstanding optoelectrical properties. However, the extremely undesired instabilities significantly hinders their development and further commercialization process. A novel tin‐based reduced‐dimensional (quasi‐2D) perovskites is reported here by using 5‐ammoniumvaleric acid (5‐AVA⁺) as the organic spacer. It is demonstrated that by introducing appropriate amount of ammonium chloride (NH₄Cl) as additive, highly vertically oriented tin‐based quasi‐2D perovskite films are obtained, which is proved through the grazing incidence wide‐angle X‐ray scattering characterization. In particular, this approach is confirmed to be a universal method to deliver highly vertically oriented tin‐based quasi‐2D perovskites with various spacers. The highly ordered vertically oriented perovskite films significantly improve the charge collection efficiency between two electrodes. With the optimized NH₄Cl concentration, the solar cells employing quasi‐2D perovskite, AVA₂FA_n?1Sn_nI_3n+1 (<n> = 5), as light absorbers deliver a power conversion efficiency up to 8.71%. The work paves the way for further employing highly vertically oriented tin‐based quasi‐2D perovskite films for highly efficient and stable photovoltaics.     

Reversible Transformation between CsPbBr3 Perovskite Nanowires and Nanorods with Polarized Optoelectronic Properties

CsPbX₃ (X = Cl, Br, I) perovskite nanowires and nanorods are important 1D and quasi 1D semiconductor nanomaterials. They have shown significant prospect in optic and optoelectronic applications, especially for their adaptability to flexible devices, good carrier transport performance, polarized absorption, and emission properties. Due to the high dependence of the property to the morphology, it is crucial to develop synthesis methods with continuous diameter and length tunability of the 1D/quasi 1D perovskites. In this report, a feasibly room temperature synthesis method was developed for ultrathin CsPbX₃(X = Cl, Br, I) perovskite nanowires. By aging the CsPbBr₃ nanowires (≈2*500 nm) under ambient condition with proper concentration and time, the nanowires are transformed to nanorods with controllable diameter and length. Reversibly, the nanorods can be transformed back to nanowires. Equilibrium mechanism is adopted to understand the morphology evolution, and hopefully could be generally applied to many other nano materials. The polarized optoelectronic properties of the nanowires and nanorods are interpreted by a model based on the two-channel anisotropies measurement. Polarized light detectors constructed by oriented assembled nanowires are fabricated to demonstrate their application potentials.     

High Efficiency and High Open Circuit Voltage in Quasi 2D Perovskite Based Solar Cells

An important property of hybrid layered perovskite is the possibility to reduce its dimensionality to provide wider band gap and better stability. In this work, 2D perovskite of the structure (PEA)₂(MA)_n–1Pb_nBr_3n+1 has been sensitized, where PEA is phenyl ethyl‐ammonium, MA is methyl‐ammonium, and using only bromide as the halide. The number of the perovskite layers has been varied (n) from n = 1 through n = ∞. Optical and physical characterization verify the layered structure and the increase in the band gap. The photovoltaic performance shows higher open circuit voltage (V_oc) for the quasi 2D perovskite (i.e., n = 40, 50, 60) compared to the 3D perovskite. V_oc of 1.3 V without hole transport material (HTM) and V_oc of 1.46 V using HTM have been demonstrated, with corresponding efficiency of 6.3% and 8.5%, among the highest reported. The lower mobility and transport in the quasi 2D perovskites have been proved effective to gain high V_oc with high efficiency, further supported by ab initio calculations and charge extraction measurements. Bromide is the only halide used in these quasi 2D perovskites, as mixing halides have recently revealed instability of the perovskite structure. These quasi 2D materials are promising candidates for use in optoelectronic applications that simultaneously require high voltage and high efficiency.     

Structural Determinants of the Sign of the Pyroelectric Effect in Quasi‐Amorphous SrTiO3 Films

The magnitude and direction of the permanent electric polarization in the non‐crystalline, polar phase (termed quasi‐amorphous) of SrTiO₃ in Si\SiO₂\Me\SrTiO₃\Me, (Me = Cr or W), Si\SrRuO₃\SrTiO₃, and Si\SrTiO₃ layered structures were investigated. Three potential sources of the polarization which appears after the material is pulled through a temperature gradient were considered: a) contact potential difference; b) a flexoelectric effect due to a strain gradient caused by substrate curvature; and c) a flexoelectric effect due to the thermally induced strain gradient that develops while pulling through the steep temperature gradient. Measurements show that options a) and b) can be eliminated from consideration. In most cases studied in this (Si\SrTiO₃, Si\SiO₂\Me\SrTiO₃\Me, M = Cr or W) and previous works (Si\BaTiO₃, Si\BaZrO₃), the top surface of the quasi‐amorphous phase acquires a negative charge upon heating. However, in Si\SrRuO₃\SrTiO₃ structures the top surface acquires a positive charge upon heating. On the basis of the difference in the measured expansion of the upper and lower surfaces of the SrTiO₃ layer in the presence and absence of SrRuO₃, we contend that the magnitude and direction of the pyroelectric effect are determined by the out‐of‐plane gradient of the in‐plane strain in the SrTiO₃ layer while pulling through the temperature gradient.     

Conformal Multifunctional Titania Shell on Iron Oxide Nanorod Conversion Electrode Enables High Stability Exceeding 30 000 Cycles in Aqueous Electrolyte

Iron oxide is promising for use in aqueous energy storage devices due to the high capacity, but one of the most challenging problems is cycling instability within the large potential window that results from the complete quasi‐conversion reaction. Herein, a conformal surface coating strategy toward iron oxide via atomic layer deposition (ALD) is presented and an Fe₃O₄@TiO₂ core–shell nanorod array anode is reported that exhibits remarkable cycling performance exceeding 30 000 times within a wide potential window in neutral lithium salt electrolyte. ALD offers a uniform and precisely controllable TiO₂ shell that not only buffers the inner volume expansion of Fe₃O₄, but also contributes extra capacity through Li⁺ intercalation/de‐intercalation and helps to alleviate the water electrolysis. Furthermore, by pairing with a pseduocapacitive cathode of V₂O₃@carbon and using a hydrogel electrolyte of PVA‐LiCl, a unique flexible quasi‐solid‐state hybrid supercapacitor can be assembled. With a high voltage of 2.0 V, the device delivers high volumetric energy and power densities (2.23 mWh cm^?3, 1090 mW cm^?3), surpassing many recently reported flexible supercapacitors. This work highlights the importance of ALD conformal multifunctional shell to instable nanoarray electrodes in aqueous electrolytes and brings new opportunities to design advanced aqueous hybrid energy storage devices.     

Topotactic Conversion Route to Mesoporous Quasi‐Single‐Crystalline Co3O4 Nanobelts with Optimizable Electrochemical Performance

The growth of mesoporous quasi‐single‐crystalline Co₃O₄ nanobelts by topotactic chemical transformation from α‐Co(OH)₂ nanobelts is realized. During the topotactic transformation process, the primary α‐Co(OH)₂ nanobelt frameworks can be preserved. The phases, crystal structures, morphologies, and growth behavior of both the precursory and resultant products are characterized by powder X‐ray diffraction (XRD), electron microscopy—scanning electron (SEM) and transmission electron (TEM) microscopy, and selected area electron diffraction (SAED). Detailed investigation of the formation mechanism of the porous Co₃O₄ nanobelts indicates topotactic nucleation and oriented growth of textured spinel Co₃O₄ nanowalls (nanoparticles) inside the nanobelts. Co₃O₄ nanocrystals prefer [0001] epitaxial growth direction of hexagonal α‐Co(OH)₂ nanobelts due to the structural matching of [0001] α‐Co(OH)₂//[111] Co₃O₄. The surface‐areas and pore sizes of the spinel Co₃O₄ products can be tuned through heat treatment of α‐Co(OH)₂ precursors at different temperatures. The galvanostatic cycling measurement of the Co₃O₄ products indicates that their charge–discharge performance can be optimized. In the voltage range of 0.0–3.0 V versus Li⁺/Li at 40 mA g^?1, reversible capacities of a sample consisting of mesoporous quasi‐single‐crystalline Co₃O₄ nanobelts can reach up to 1400 mA h g^?1, much larger than the theoretical capacity of bulk Co₃O₄ (892 mA h g^?1).     

Structural Transformations during Formation of Quasi‐Amorphous BaTiO3

A model of structural transformations of amorphous into quasi‐amorphous BaTiO₃ is suggested. The model is based on previously published data and on X‐ray photoelectron spectroscopy data presented in the current report. Both amorphous and quasi‐amorphous phases of BaTiO₃ are made up of a network of slightly distorted TiO₆ octahedra connected in three different ways: by apices (akin to perovskite), edges, and faces. Ba ions in these phases are located in the voids between the octahedra, which is a nonperovskite environment. These data also suggest that Ba ions compensate electrical‐charge imbalance incurred by randomly connected octahedra and, thereby, stabilize the TiO₆ network. Upon heating, the edge‐to‐edge and face‐to‐face connections between TiO₆ octahedra are severed and then reconnected via apices. Severing the connections between TiO₆ octahedra requires a volume increase, suppression of which keeps some of the edge‐to‐edge and face‐to‐face connections intact. Transformation of the amorphous thin films into the quasi‐amorphous phase occurs during pulling through a steep temperature gradient. During this process, the volume increase is inhomogeneous and causes both highly anisotropic strain and a strain gradient. The strain gradient favors breaking those connections, which aligns the distorted TiO₆ octahedra along the direction of the gradient. As a result, the structure becomes not only anisotropic and non‐centrosymmetric, but also acquires macroscopic polarization. Other compounds may also form a quasi‐amorphous phase, providing that they satisfy the set of conditions derived from the suggested model.     

MXene Phase with C3 Structure Unit: A Family of 2D Electrides

A new structural phase is discovered for M₂CO₂ MXenes with M = Sc, Y, La, Lu, Tm, and Ho. The hexagonal carbon layer sandwiched between M atoms, typical for MXenes, is transformed into C₃ trimers with anionic electrons localized in quasi zero-dimensional lattice spaces in-between the C₃ units, so the systems can be described as [M₆ C₃ O₆]^+II : 2e⁻ electrides. The systems are readily ionized into [M₆ C₃ O₆]^+II with very low ionization energy via an anti-doping mechanism. It is shown that this new structure of Sc₂CO₂ can bind multiple lithium atoms, with low migration barriers. The findings indicate that these M₂CO₂ MXenes with unusual carbon trimers are a new family of 2D electride insulators with the potential for charge storage applications, thermal field emission, and as anode material in lithium batteries.     

Anisotropic Growth of Nonlayered CdS on MoS2 Monolayer for Functional Vertical Heterostructures

2D semiconductors have emerged as a crucial material for use in next‐generation optotelectronics. Similar to microelectronic devices, 2D vertical heterostructures will most likely be the elemental components for future nanoscale electronics and optotelectronics. To date, the components of mostly reported 2D van der Waals heterostructures are restricted to layer crystals. In this work, it is demonstrated that nonlayered semiconductors of CdS can be epitaxially grown on to 2D layered MoS₂ substrate to form a new quasi vertical heterostructure with clean interface by chemical vapor deposition. Photodetectors based on this CdS/MoS₂ heterostructure show broader wavelength response and ≈50‐fold improvement in photoresponsivity, compared to the devices fabricated from MoS₂ monolayer only. This research opens up a way to fabricate a variety of functional quasi heterostructures from nonlayered semiconductors.