高性能Ag/AgI红外空芯光纤的研究

采用液相化学镀膜法研制了内面镀有银膜和碘化银膜(Ag/AgI)的高性能空芯红外光纤.分析了绿色导航光和红外激光同时低损耗传输的光纤结构参量.长度1 m、内直径0.7 mm的Ag/AgI空芯光纤不仅在红外有低损耗传输特性,而且首次在波长530 nm处获得了7 dB/m的低传输损耗特性.满足可见光作为导航光的同轴传输要求.通过分析和改进实验工艺参量,有效降低Ag和AgI薄膜的表面粗糙度.给出了高性能Ag/AgI空芯光纤的介质镀膜的具体工艺参量.     

Self-guiding of infrared and visible light in photonic crystal slabs

We experimentally demonstrate diffractionless guidance and efficient routing of light in two-dimensional photonic crystal slabs at infrared and visible wavelengths. Our particular design allows for simultaneous guidance of TE and TM polarized light beams at the same wavelength. Routing performance and possibilities of propagation loss reduction are investigated experimentally. Experimental results are in excellent agreement with three-dimensional simulations.     

Multiwavelength laser light transmission of hollow optical fiber from the visible to the mid-infrared

We report on low-loss multiwavelength laser delivery of hollow optical fiber in a wide wavelength region, from the visible to the infrared. Improved methods of liquid-phase coating were used to fabricate the hollow fiber with inner films of a silver and a cyclic olefin polymer (COP) layer. The surface roughness of the silver layer was reduced dramatically by pretreatment on the inner glass surface with an SnCl2 solution. The COP layer roughness was also decreased by using an ambient atmosphere of tetrahydrofuran (THF) solvent during the COP layer formation. Owing to the smooth surfaces, hollow fiber with optimum COP film thickness for CO2 laser light simultaneously yields low losses for a Er:YAG laser and a red pilot beam. The power durability of CO2 and Er:YAG lasers, as well as the loss properties for the pilot beam, is demonstrated.     

Optical properties of AgI/Ag infrared hollow fiber in the visible wavelength region

We report on AgI/Ag infrared hollow fiber with low-loss in visible region. Improved methods of silver plating and iodination were proposed to fabricate the hollow fiber. The surface roughness of the silver layer and the silver iodide layer was reduced by the pretreatment with an SnCl2 solution and low iodination temperature. Losses for the Er:YAG and green laser light were 0.4 and 7dB/m. The loss property of green laser beam was low to deliver a pilot beam for the invisible infrared laser light. Owing to the smooth and uniform AgI film, the loss spectrum of the hollow fiber showed clear interference peaks in the visible region. An empirical formula for AgI material dispersion was derived, which is of special importance for the design of high-performance AgI/Ag hollow fiber.     

PSDF of log-amplitude scintillation for 7 μm band laser beam with absorption by water vapour

The power spectral density function (PSDF) of the log-amplitude scintillation for an infrared laser beam was measured experimentally. To investigate the contribution of the absorption and the dispersion that cause the scintillation, we chose 16 wavelengths of infrared light and one wavelength of visible light. It is found that the spectral density of scintillation for the infrared beam does not agree with that for the visible beam, as predicted by Tatarskii's theory in the low-frequency region below 1 Hz. This disagreement between the experiment and the theory in the low-frequency region should be attributed to water vapour absorption.     

β-BaB2O4 deep UV monolithic walk-off compensating tandem

The generation of watt-level cw narrow-linewidth sources at specific deep-UV wavelengths corresponding to atomic cooling transitions usually employs external cavity-enhanced second-harmonic generation (SHG) of moderate-power visible lasers in birefringent materials. Among the oxo-borate materials, barium borate (β-BaB₂O₄ or BBO) combines the highest UV band edge and largest nonlinearity but suffers from large walk-off angles that limits the nonlinear interaction length. Alternative quasi-phase-matched (QPM) ferroelectrics are hardly suited for cavity-enhanced operation due to their much larger UV absorption and associated photo-refractive and thermal lensing effects, in addition to the difficult fabrication of fine-pitch domain gratings for short UV coherence lengths. In this work, we investigate an alternative approach to cw deep-UV generation by employing the low-loss BBO in a monolithic walk-off compensating structure [J.-J. Zondy, Ch. Bonnin, D. Lupinski, J. Opt. Soc. Am. B 20 (2003) 1675] to simultaneously enhance the effective nonlinear coefficient while minimizing the UV beam ellipticity under tight focusing. As a preliminary step to cavity-enhanced operation, and in order to apprehend the design difficulties stemming from the extremely low acceptance angle of BBO, we investigate and analyze the single-pass performance of a L_c = 8 mm monolithic walk-off compensating structure made of 2 optically-contacted BBO plates cut for type-I critically phase-matched SHG of a cw λ = 570.4 nm dye laser. As compared with a bulk crystal of identical length, a sharp UV efficiency enhancement factor of 1.65 has been evidenced with the tandem structure, but at ∼−1 nm from the targeted fundamental wavelength, highlighting the sensitivity of this technique when applied to a highly birefringent material such as BBO. Solutions to angle cut residual errors are identified so as to match accurately more complex periodic-tandem structure performance to any target UV wavelength, opening the prospect for high-power, good beam quality deep-UV cw laser sources for atom cooling and trapping.     

复杂辐射环境与武器装备试验评估

从业内普遍接受的电磁环境和武器装备电磁环境效应概念入手,提出了复杂辐射环境概念,解释了其内涵和意义;围绕军事问题,探讨了辐射环境的基本构成,从辐射来源上突出了水声环境、电磁环境、光学环境和核辐射环境四个剖面,从效应考虑又将其分解为自然辐射环境、自扰互扰辐射环境、背景辐射环境和威胁辐射环境四个剖面,指出了这些剖面的统计独立性;根据辐射环境结构、特性和信息承载效应,定义了辐射环境的复杂度,介绍了辐射对抗的基本原理;指出复杂辐射环境下武器装备试验与评估问题与传统问题一样,仍是个概率统计问题,并且给出了可按环境剖面进行分解的高效简便的试验与评估方法。     

Broadband four-wave optical parametric amplification in bulk isotropic media in the ultraviolet

We report on four-wave optical parametric amplification of the ultrashort ultraviolet light pulses in bulk fused silica and CaF₂. Exact phase-matching in these isotropic media is achieved by means of non-collinear interaction with cylindrical beam focusing. Four-wave optical parametric amplifier efficiently operates in the UV spectral range with 1-ps laser pulses, delivering amplified signal energy exceeding 50 μJ using millijoule pump pulses in the visible (527 nm). Results of scanning of the parametric gain profile suggest that broad amplification bandwidth as wide as ∼20 nm (at FWHM) under these experimental settings is achieved, which might support amplification of sub-10-fs ultraviolet pulses with central wavelength around 330 nm. It is also shown experimentally and verified theoretically that the parametric gain profile exposes a distinct inhomogeneity and its bandwidth notably broadens due to effects of self- and cross-phase modulation imposed by the intense pump beam.     

Enlarging lens design with f-Θ lens for real time laser lithography inspections

An enlarging lens, composed of a charge-coupled-device (CCD) lens and an f-Θ lens, has been designed for real time laser lithography visual inspection purposes. The object of this design is to enlarge the image of the working specimens in real time, which used to be done by an independent magnifying system after the lithography process. F-Θ lens has both roles in this design, being a laser lithography lens and a specimen imaging lens. A beam splitter has been inserted between the f-Θ lens and the CCD lens, which divides the UV laser beam and the visible beam to form a coaxial system. This design also reaches the image requirements in both wavelength bands, that the value of MTF is nearly diffraction-limit in UV wavelength and greater than 0.45 at 40 c/mm in visible wavelength.     

增强CCD紫外和极紫外成像的荧光物质的研究

CCD广泛用于可见光和近红外波段的成像,为了使CCD也能在紫外和极紫外波段成像,波长转换十分有用。采用对此波段敏感的荧光物质,使辐射到CCD上的紫外和极紫外光转换成可见光,CCD便可对其成像。研究了产生荧光的过程和条件以及用于把紫外和极紫外光转换成可见光的荧光物质需要满足的条件后,发现水杨酸钠、四苯基-丁二烯、六苯并苯和路玛近比较合适,并简明介绍了它们的特性和制备方法。评述了该领域的荧光物质物质的应用前景以及需要改进的方面。     

Optics in curved space

We experimentally study the impact of intrinsic and extrinsic curvature of space on the evolution of light. We show that the topology of a surface matters for radii of curvature comparable with the wavelength, whereas for macroscopically curved surfaces only intrinsic curvature is relevant. On a surface with constant positive Gaussian curvature we observe periodic refocusing, self-imaging, and diffractionless propagation. In contrast, light spreads exponentially on surfaces with constant negative Gaussian curvature. For the first time we realized two beam interference in negatively curved space.     

铌酸锂晶体紫外激光诱导畴反转实验研究

报道了在铌酸锂晶体中实现紫外激光诱导畴反转的实验。在一定外加均匀电场下,铌酸锂晶体中通过波长365nm的紫外激光,由于紫外光的照射降低了矫顽电场只在通光区实现畴反转。研究表明,该方案可用于周期性极化铌酸锂的制备,并有望成为制作精细周期性畴结构的有效技术方案。     

准分子激光束的喇曼整形

受激喇曼散射可以将紫外准分子激光辐射频移到特定的近紫外和可见光波长.采用喇曼整形技术还可以获得衍射极限发散角的斯托克斯输出.本文研究了注入光束质量对喇曼整形的影响,并求得不同氢压力下的喇曼增益系数和饱和参量.     

Effect of rhodium doping on the photorefractive properties of BCT crystals at 850 nm

We present an experimental investigation of the photorefractive properties of rhodium-doped barium calcium titanate (BCT) crystals of the congruent melting composition Ba_0.77Ca_0.23TiO₃. Considering the results previously obtained on this crystal in the visible region, it should be a good alternative to BaTiO₃. Nevertheless, many applications use infrared light. Therefore we present here a study of rhodium-doped BCT crystals at 850 nm. This wavelength is of special interest as it is in the spectral range of laser diodes. Rhodium doping is expected to enhance the sensitivity of the crystal in the infrared as is the case for BaTiO₃.We first noticed that BCT:Rh crystals are sensitive at this wavelength as expected. Furthermore, the photorefractive properties are interesting in terms of photorefractive gain, with a gain as high as 3 cm^-1 with ordinary polarization. This study has also put forward the fact that rhodium is not the only defect that participates in the photorefractive effect. Indeed, a large quantity of iron seems to be present in the BCT crystals and to participate in the photorefractive effect.An Erratum to this article can be found at     

基于2D微电子机械系统(MEMS)镜全向激光雷达光学系统设计

为了满足全向激光探测的需求,提出一种基于2DMEMS镜扫描的激光雷达结构。激光器通过1×6高速光开关分时地给6个扫描子系统提供光信号,6个扫描子系统探测视场叠加起来可实现360°激光探测。每个扫描子系统的扫描范围为60°×30°,其中包含一个扩展MEMS镜扫描角度的发射光学天线和一个大视场有增益的接收光学天线。发射光学天线将MEMS镜±10°的扫描角扩展到±30°,发散度小于0.2mrad;接收视场内的激光波经过接收天线在探测器上所成的半像高小于1mm,接收增益为3.65。通过计算修正后的激光雷达方程可得到发射功率20 W的激光束在工作距离100 m内的回波功率≥1 nW,结果表明该光学系统可适用于激光雷达系统。     

Fabrication of fluorocarbon polymer-coated silver hollow-glass waveguides for the infrared by the liquid-phase coating method

Fluorocarbon polymer-coated silver hollow-glass waveguides have been fabricated based on the method of silver mirror reaction for silver, and the dipping method for the fluorocarbon polymer. The waveguides show low-loss properties for the infrared wavelengths except for the wavelength regions of large absorption of the polymer. Er:YAG laser light has been successfully transmitted through the flexible waveguides with small bending losses.     

微结构气体探测器中紫外激光束的信号和指向精度实验研究

在气体探测器研究中,利用266 nm紫外激光的双光子电离物理机制使气体电离产生可测量的信号,是一种重要的标定方法.随着微结构气体探测器(MPGD)的不断发展,用紫外激光标定来实现较高精度位置分辨率成为了一种研究需求,对此有两个关键技术问题需要解决:实验研究激光可测信号大小以及激光指向精度.分析和模拟计算了紫外光电离信号大小和激光调光误差,基于微结构气体电子倍增器探测器与266 nm波长激光束,在工作气体Ar/CO_2(70/30)中,测量了不同光斑面积与输出信号的关系;设计和研制了紫外激光调光系统,实验测量了紫外光调光偏差.模拟结果与实验结果对比分析表明:紫外激光束作用于气体探测器,探测器增益在5000,前放增益为10 mV/fC时, 6 mm读出条宽输出信号幅度约400 mV;在探测器内传播距离为400 mm时,较短时间内(10—20 min)实验调光指向精度可以保证小于5′,引入z向偏差最大可以达到0.33 mm,对应z向漂移速度的测量相对误差为6.4×10-4.该研究为MPGD与紫外激光标定实验设计提供主要的设计参考.     

Amplification mechanism of ion-ripple lasers and its possibleapplications

The ion-ripple laser (IRL) is an advanced scheme for generating coherent high-power radiation, in which a relativistic electron beam propagates obliquely through an ion ripple in a plasma. Its amplification mechanism is described by a low gain theory, while the linear growth rate is given by the dispersion relation. The efficiency of the lasing is determined by the nonlinear saturation mechanism discussed. By proper choice of device parameters, sources of microwaves, optical, and perhaps even X-rays can be made. The availability of tunable sources for wide wavelength regimes, coherence and high-power, as well as lower cost and simplicity of equipment, are emphasized     

考虑钕玻璃放大器增益特性的光谱色散匀滑系统性能研究

采用数值方法研究了钕玻璃放大器的增益特性对高功率激光系统中光谱色散匀滑单元性能的影响.分析结果表明,入射光中心波长与放大器增益曲线中心波长不一致时,焦斑强度分布会受到一定的影响,且该影响随放大倍数增大趋于明显,而两个波长一致时,强度分布变化较小.靶面焦斑整体的辐照均匀性则主要取决于经过相位调制后的激光束的带宽,放大器的增益特性对其空间功率谱及均匀性无明显的影响.所得结论为光谱色散匀滑单元在激光系统中的实际应用提供了重要的理论参考.     

远红外自由电子激光器的性能和可能的应用(英文)

本文提出了远红外自由电子激光器(FIRFEL)的现实优点:对电子束质量要求不太苛刻;比较经济;对远红外区的非线性和相干性研究是唯一的合适的光源。分析了自由电子激光器增益与电子束和摆动器参量的关系,指出对给定的发射度存在一特定的波长,当波长比特定波长短时,增益将急骤下降。概述了远红外区的重要物理现象以及远红外自由电子激光器的可能的应用,预期这些研究对THz电子学发展是很重要的。