新型二维材料碳化钛纳米片光限幅特性研究

作为一类新型二维纳米材料,金属碳/氮化物纳米片（MXene）具有高的比表面积和电导率,以及组分、层数与厚度灵活可控的优点,在储能、催化、传感和光学等领域具有潜在应用价值。研究了一种MXene材料碳化钛（Ti3C2TX）纳米片分散液的非线性光学效应及其响应机制。发现Ti3C2TX纳米片分散液在532、1 064 nm纳秒脉冲激光作用下表现出优异的光限幅性能,其限幅阈值分别为0.14 J/cm2和0.12 J/cm2;通过测量非线性散射光强度随入射光功率密度的依赖关系,发现该材料光限幅响应机制主要起源于非线性光学散射效应。与传统的光限幅材料C60比较,该材料具有光限幅阈值低、响应波长范围宽等优点。     

聚丁二炔光限幅材料

研究了５－（２－硫甲基－４－甲基－５－嘧啶基）－２，４－戊二炔－１－醇对甲苯磺酸酯（ＰＤＡＴＳ）的光限幅性能。与现有的光限幅材料相比，这种材料具有线性透射率高、限幅幅值和限幅阈值低等优点，在线性透过率为８７％时．其限幅幅值和限幅阈值分别为Ｅｃ＝１８０ｍＪ／ｃｍ２，Ｅｔｈ＝１５０ｍＪ／ｃｍ２     

光限幅技术新进展

光限幅技术是基于非线性光学原理实现激光防护的技术。概述了光限幅基本原理,总结了光限幅技术的发展,比较分析各种光限幅效应与光限幅材料的优劣,介绍了光限幅材料新进展。     

酞菁类光限幅功能材料

酞菁及其衍生物是一类能在相当宽的紫外可见吸收光谱范围内通过激发态吸收过程限制纳秒激光脉冲强度的理想光限幅材料之一,可以保护人眼、光学仪器、传感器等免受激光损伤.由于酞菁分子结构的灵活性,可以在很大程度上通过结构设计或修饰来调节其光限幅响应能力.对酞菁进行轴向取代修饰能有效地防止材料聚集行为,增强材料的非线性光学和光限幅能力.这类酞菁的纳秒非线性吸收和光限幅行为主要取决于电子吸收谱中位于Q-带和B-带之间的激发态吸收性能.着重介绍了近年来基于可溶性轴向和侧基取代的酞菁及其衍生物的光限幅功能材料研究的最新进展.     

非线性光限幅材料的研究进展

通过对线性、非线性以及相变激光防护材料性能的简要比较,综合分析半导体材料、金属酞菁类化合物、C60及其衍生物、无机金属团簇化合物及碳纳米管材料的光限幅特性.基于碳纳米管材料具有限幅阈值低、限幅波段宽、响应时间短等优势,进一步论述了其在光限幅应用中的研究进展,指出该光限幅材料在材料化及器件化方面需要更深入的探索,以期能够更好地用于光限幅领域.     

富勒烯光限幅技术研究新进展

介绍了富勒烯激发态吸收光限幅以及激发态吸收和其它非线性光学效应共同作用的复合型光限幅技术的研究新进展。分析了今后的研究方向。     

光限幅材料的研究现状及其在激光防护中的应用

随着激光武器的发展,对相应的对抗措施不断提出更高的要求。光限幅材料体在对抗激光干扰与致盲武器中具有重要的研究价值。作者简要介绍了近年来光限幅材料的研究情况及其在这一对抗领域中的应用研究。     

富勒烯的功率光限幅特性

应用时间分辨技术研究了富勒烯溶液的激发态吸收瞬态功率光限幅特性,在实验条件下,其功率光限幅的开关速度约为5 ns.     

理想自聚焦和自散焦光限幅的分析

分析产生非线性相移的光束在一个附加线性透镜焦平面区域的强度分布图,研究非线性自聚焦和自散焦的机制,以期获得理想自聚焦、自散焦光限幅的能力。     

理想聚焦系统光限幅效应的理论分析

本文利用高斯分解法对聚焦光学系统中非线性介质引起的光限幅效应进行了优化分析,首次讨论了远场和近场（焦平面上）几何排布下的光限幅效应和灵敏度,且详细地分析了远场情况光限幅效应与样品到小孔距离的关系。     

Optical limiting in GaAs

We have used two-photon absorption, self-defocusing, and optically-induced melting in GaAs to limit 1 μm picosecond pulsed radiation. The contribution to the limiting action from each of these mechanisms is discussed and demonstrated. Additionally, we measure a two-photon absorption coefficient of 26 cm/GW, which is in good agreement with the smallest values reported in the literature. A pulse-width study of the nonlinear absorption was conducted to isolate the effects of two-photon-generated free-carrier absorption. Results indicate that, even though the number of free-carriers is sufficient to severely defocus the incident beam, free-carrier absorption does not measurably contribute to the nonlinear absorption.     

利用热自散焦实现的激光限幅

本文详细研究了利用热自散焦效应实现的对连续激光的光限幅。给出了一个描述限幅器输出功率特性的解析表达式,实验和理论计算较好地符合。     

Low-noise two-dimensional electron gas FET

Two-dimensional electron gas FETs (TEGFETs) have been fabricated on an N-AlGaAs-GaAs heterojunction. Microwave results at 10 GHz are: NF=2.3 dB, Gass=10.3 dB and Gmax=13.2 dB. These first results obtained on nonoptimised material and processing suggest that TEGFET can be superior to a conventional GaAs FET.     

VLSI implementation of two-dimensional digital filters via two-dimensional filter chips

The realization of an arbitrary two-dimensional (2-D) rational transfer function which represents an infinite impulse response (IIR) 2-D filter in terms of low-order 2-D polynomials is discussed. These low-order polynomials are implemented via a bit-sliced chip, and are used as standard building blocks for the implementation of the general 2-D digital filter. Different general realization methods are considered and are modified in order to incorporate the standard 2-D chips. The resulting structures have reduced complexity and they exhibit a high degree of regularity and modularity. Furthermore, the number of 2-D low-order filter chips required for the implementation of the given filter is substantially reduced, compared to the number of 1-D chips required by regular general implementations.     

Optical and confinement properties of two-dimensional photoniccrystals

We describe experiments on a quasi-two dimensional (2-D) optical system consisting of a triangular array of air cylinders etched through a laser-like Ga(Al)As waveguiding heterostructure. Such a configuration is shown to yield results very well approximated by the infinite 2-D photonic crystal (PC). We first present a set of measurements of the optical properties (transmission, reflection, and diffraction) of slabs of these photonic crystals, including the case of in-plane Fabry-Perot cavities formed between two such crystals. The measurement method makes use of the guided photoluminescence of embedded quantum wells or InAs quantum dots to generate an internal probe beam. Out-of-plant, scattering losses are evaluated by various means. In a second part, in-plane micrometer-sized photonic boxes bounded by circular trenches or by two-dimensional photonic crystal are probed by exciting spontaneous emission inside them. The high quality factors observed in such photon boxes demonstrate the excellent photon confinement attainable in these systems and allow to access the detail of the modal structure. Last, some perspectives for applications are offered     

Boundary instability of a two-dimensional electron fluid

It was shown previously that the current-carrying state of a Field Effect Transistor with asymmetric source and drain boundary conditions may become unstable against spontaneous generation of plasma waves [1]. By extending the analysis to the two-dimensional case we find that the dominant instability modes correspond to waves propagating in the direction perpendicular to the current and localized near the boundaries. This new type of instability should result in plasma turbulence with a broad frequency spectrum. More generally, it is shown that a similar instability might exist, when a strong enough current goes through a single boundary between the gated and ungated regions. The text was submitted by the authors in English.     

Optical power limiting and stabilization based on a novel polymercompound

Optical power limiting and stabilization based on the two-photon absorption (TPA) mechanism is performed in a polymer solution excited by ~810 nm and ~7-ns laser pulses. The solute is a novel polymer, a poly(2,5-dialkoxy-p-phenylene ethynylene) derivative (EBO-OPPE). Using 1-cm path-length EHO-OPPE solution in chloroform of d₀=0.03 mol of repeat unit/liter as the nonlinear absorptive medium, the dynamic transmission changes from T=0.92 to 0.28 when the input intensity of the ~810-nm laser beam is increased from I₀=15 to 600 MW/cm² . The measured nonlinear absorption coefficient is 14.5 cm/GW. Optical power stabilization is demonstrated at an average input intensity level of I₀≈400 MW/cm² with a Δ≈±25% peak-power fluctuation of the laser pulse. After passing through the nonlinear medium, the output peak-power fluctuation is reduced to Δ≈±8%. The spectral-width effect of the input laser beam on the nonlinear absorption of the EHO-OPPE solution is investigated. For three different spectral structures of the input laser beam (single narrow spectral line, multiple spectral lines, and broad spectral band), measured values of TPA cross section for EHO-OPPE are σ₂=66, 80, and 101×10^-20 cm⁴/GW, respectively. This means that EHO-OPPE is one of the best known nonlinear absorptive materials for power limiting purposes     

Plasma instabilities in quasi two-dimensional electron gases

Recent pulsed optical experiments in n-doped quantum wells (Knox and co-workers, 1988) suggest that hot carriers relax in times as short as 10 fs. A 10 fs thermalization time is an order of magnitude shorter than the inverse plasma frequency. While Monte Carlo calculations (Goodnick and Lugli, 1988) can account for the trends in such hot carrier relaxation experiments, times as short as 10 fs are difficult to understand. As an alternative to single-particle relaxation mechanisms, we have considered the possibility of collective mode instabilities in these systems. In this paper, the longitudinal dielectric function for a quasi-two-dimensional electron gas is calculated, in the random phase approximation, for a plasma with a shell-like, excited component, analogous to that excited in the experiments of Knox, and co-workers. From this dielectric function, the plasma eigenfrequencies are determined. In this excited plasma, intrasubband plasma modes experience gain by inverse Landau damping, via coupling to the energetic electrons. Their repsonse contrast with the Landau damped behavior of the corresponding modes in a three dimensional plasma. The modes with gain are unstable, and experience amplification at rates on the order of the plasma frequency, relaxing energy from the excited distribution. While these growth rates are not fast enough to account for the observed relaxation rates in the n-doped quantum wells studied by Knox, and co-workers, the calculations do indicate an alternative relaxation path, whose rate increases linearly with density, and imply that two-dimensional plasmas are less stable than those in three dimensions.     

Optical and electrical properties of two-dimensional anisotropic materials

Two-dimensional(2D) anisotropic materials, such as B-P, B-As, GeSe, GeAs, ReSe2, KP15 and their hybrid systems, exhibit unique crystal structures and extraordinary anisotropy. This review presents a comprehensive comparison of various 2D anisotropic crystals as well as relevant FETs and photodetectors, especially on their particular anisotropy in optical and electrical properties. First, the structure of typical 2D anisotropic crystal as well as the analysis of structural anisotropy is provided. Then, recent researches on anisotropic Raman spectra are reviewed. Particularly, a brief measurement principle of Raman spectra under three typical polarized measurement configurations is introduced. Finally, recent progress on the electrical and photoelectrical properties of FETs and polarization-sensitive photodetectors based on 2D anisotropic materials is summarized for the comparison between different 2D anisotropic materials. Beyond the high response speed, sensitivity and on/off ratio, these 2D anisotropic crystals exhibit highly conduction ratio and dichroic ratio which can be applied in terms of polarization sensors, polarization spectroscopy imaging, optical radar and remote sensing.