Ablation of microstructures applying diffractive elements and UV femtosecond laser pulses

A new method for simple and economic fabrication of diffractive optical elements (DOEs) with three and four phase levels, by UV nanosecond (ns) laser ablation is presented. The technique is based on the combination of two sequentially generated complementary 2-level phase elements. During the fabrication, complete ablative removal of a highly absorbing silicon suboxide layer by pixelated backside illumination ensures the necessary high precision and optical quality. Full functionality of the new DOEs is demonstrated by fabricating micro-structures using UV femtosecond pulses.     

Morphology studies of the metal surfaces with enhanced absorption fabricated using interferometric femtosecond ablation

Recently, the enhancing of bulk metals optical absorption with focused femtosecond pulses was demonstrated. This absorption enhancement is caused by different nano- and micro-structures which are formed during laser ablation with ultrashort pulses. In this paper we study the evolution of the surface structures using interferometric ablation and compare it to normal fs-ablation. Previously we have shown that interferometric femtosecond ablation is an efficient method to fabricate absorbing metal surfaces. In this study we ablated large areas of hole-array structures with different pulse numbers in polished stainless steel and copper samples. The evolution of surface morphology and the depth of the holes for these structured surfaces are presented. In addition, the reflectance of laser generated surface structures are measured at the wavelength range of 200–2300 nm using a standard spectrophotometer.     

飞秒激光辐射诱导金属表面微纳结构研究

通过1 kHz的飞秒脉冲(脉宽130 fs,中心波长800 nm)对厚度为60 μm的不锈钢65Mn表面进行飞秒微加工,通过拟合得到65Mn的消融阈值为0.5 J·cm-2。研究了飞秒激光作用下表面形成的多种微结构,其中包括纳米孔及纳米柱状物。同时讨论了激光能量和作用脉冲个数对微结构形成的影响。随着周期波纹结构的形成,发现在各种能量和脉冲个数条件下,周期结构的周期约为入射脉冲的波长。相同的激光功率下,在不同加工速度和加工次数下对不锈钢进行表面微加工,得到了规则的圆孔阵列结构。     

Pulse-parameter dependence of the configuration characteristics of a micro-structure in fused SiO2 induced by femtosecond laser pulses

The fabrication of a micro-structures in fused SiO₂ by femtosecond laser pulses was studied in the range of pulse duration 150∼500 fs, pulse energy 60 nJ to ∼7 μJ and wavelengths 400 nm and 800 nm. The characteristics of the cross section of the micro-structure were explained with the multiphoton-ionization and avalanche-ionization processes in the femtosecond laser-induced breakdown. The characteristics of the longitudinal length of the micro-structure relating to the direct-focusing and self-action effects are also discussed. Received: 10 January 2001 / Accepted: 7 April 2001 / Published online: 23 May 2001     

Phase diagrams of laser-processed nanoparticles of brass

Nanoparticles of brass are prepared by ablation of a brass target in ethanol using radiation of a copper-vapor laser at various laser fluences. The nanoparticles are characterized by TEM and optical spectroscopy. The multipulse laser irradiation leads to formation both the nanoparticles in liquid and well-ordered micro-structures on a surface of a target. It is revealed that both the morphology and absorption spectra of brass nanoparticles depend on presence of the micro-structures. Nanoparticles with the various phase diagrams are formed from a flat brass surface and from the same surface with micro-structures. The results are compared with a model of phase diagrams, in which size and composition effects are taken into account.     

飞秒激光的波长对SiC材料烧蚀的影响

利用10倍的显微物镜将近红外飞秒激光脉冲汇聚到宽带隙半导体材料6H SiC的前表面,研究样品的烧蚀及诱导微细结构。用扫描电镜(Scanning electron microscope,SEM)及光学显微镜测量烧蚀斑。利用烧蚀面积与激光脉冲能量的关系确定SiC的烧蚀阈值。给出了SiC样品的烧蚀阈值与飞秒激光波长的依赖关系。实验结果表明,可见光区随波长增加,烧蚀阈值从0.29J/cm2增加到0.67J/cm2;而在近红外区,SiC的烧蚀阈值为0.70J/cm2左右,基本上不随激光波长变化而改变。结合计算结果,可以认为在飞秒激光烧蚀SiC的过程中,在近红外区,光致电离和碰撞电离均起到了重要的作用;而在可见光区,光致电离的作用相对大一些。     

Micro-hot-embossing of 316L stainless steel micro-structures

In this paper, the fabrication of an array of 316L stainless steel cylindrical micro-structures by hot-embossing is studied. The effects of various embossing parameters on the filling of the micro-cavities of silicon mold insert and the demolding of micro-structures are investigated. They include different silicon mold insert configurations, embossing pressure, embossing temperature, embossing time and the thickness of embossing substrate on which the micro-structures stand. Two types of silicon mold insert configurations are investigated. Hot-embossing study with the silicon mold insert attached on the upper mold plate shows that it is not feasible to achieve complete filling. Incomplete filling occurs and increasing the embossing pressure causes excessive thinning of the embossing substrate, so that micro-structures are torn off during demolding. Experiments show that the configuration that the silicon mold insert is positioned flush with lower mold surface improves complete filling. Using suitable embossing pressure and temperature, the larger substrate thickness and longer embossing time ensure the fabrication of defect-free fully filled micro-structures.     

不同气体环境下532nm激光诱导硅表面形貌的研究

研究了在不同气体环境下,利用532nmNd：YAG纳秒脉冲激光累积辐照单晶硅表面形成的微结构,结果表明,在其他条件相同,背景气体不同的情况下,背景气体对硅表面形貌的形成起着重要的作用。具体分析了真空、N2和SF6 3种环境气氛下形成的微结构,结果显示,在sF6中形成的锥形微结构的数密度比在N2和真空中的大,并且锥形具有更大的纵横比;在N2、真空和sF6中形成的微结构尺寸依次减小。sF6气氛下,激光辅助化学刻蚀的效率比在真空和N2气氛中的高。另外,辐照区域边缘有波纹微结构形成,分析认为,该微结构的形成是由表面张力波的冷却导致的。     

Laser-assisted growth of microstructures on spatially confined substrates

Laser-assisted growth of microstructures on spatially confined substrates is experimentally studied. The experiments are performed using a copper-vapor laser with pulse duration of 20 ns, and repetition rate of 7.5 kHz. Ropes made of Ni-Cr wires with diameter of 50-100 μm, as well as the edge of 50 μm thick Ni foils were exposed to multiple laser pulses. The morphology of structures that grow on these targets drastically differs from periodic array of micro-cones observed on semi-infinite targets made of the same materials. In case of wires the structures have radial symmetry and do not show any periodicity, while in case of a foil the periodic structures are aligned along its edges. The model of micro-structures formation in spatially confined conditions is elaborated based on the numerical solution of the heat conduction and hydrodynamics equations. It is shown that boundary conditions imposed by confined target onto melt flow strongly affect the structure morphology. The micro-structure formation is related to the confinement of melt flow under combined action of both capillary forces and gradients of surface tension.     

激光烧蚀高纯Zn形成的微米金属球体对后续脉冲激光的耦合增强效应

脉冲激光束在低真空(约2 Pa)环境下聚焦到高纯Zn靶表面, 烧蚀区域不仅有中心深孔的宏观损伤, 而且还发现大量微米量级的类似足球形状的金属Zn球体结构附着生长在孔洞内侧表面. 实验过程中采用等离子体光谱诊断技术研究宏观和微观损伤对后续脉冲激光的影响程度. 与聚焦于金属Zn平滑表面相比, 宏观损伤可以使后续激光诱导的Zn原子334.5 nm谱线强度提高10.3%, 在此基础上大量Zn微米球体附着在内表面可以使谱线强度再提高34.3%. 因此, 推断这些金属Zn微球表面镶嵌着光洁的纳米量级六边形和五边形小平面, 可以对后续脉冲激光产生镜面反射, 使得激光能量汇聚并耦合增强, 提高烧蚀效率. 实验结果还表明, 这些微米球体的数目随着激光脉冲次数的增加而增多, 使得后续激光能够诱导产生更为致密高温的等离子体. 研究结果有望为激光-金属微孔技术提供新思路. 关键词： 脉冲激光烧蚀 微纳米结构 激光诱导等离子体     

Structure and transport properties of charged sphere suspensions in (local) electric fields

Motivated by both still open fundamental theoretical questions as well as novel applications, the electro-kinetics of highly charged model colloids have attracted considerable interest in the last few years. The present paper reviews corresponding new developments and trends emerging mainly from novel instrumentations for both strongly interacting and extremely dilute systems. We also highlight recent uses of local electric fields and electro-kinetic currents to realize complex micro-swimmers or prescribe crystal micro-structures.     

Theoretical and experimental approach to the texturization process of bioreactive surfaces by high-power laser

The properties of orthopaedic/dental implants can be tuned through the laser surface modifications that take place during a laser ablation process. Processing assisted by a laser is adequate to produce macro- and micro-structures on metallic alloys and polymer surfaces in order to improve their biological response.     

颗粒多孔层在真空状态下的沸腾两相流与传热

在前文［１］实验研究的基础上，利用带液池的多孔壁微热虹吸蒸发段模型，对颗粒多孔薄层在真空状态下的沸腾两相流与传热进行了分析，综合实验数据，建立了传热关联式。     

Multi-wavelength phase-shifting interferometry for micro-structures measurement based on color image processing in white light interference

Conventional multi-wavelength phase-shifting interferometry utilizes two or three monochromatic light sources, such as lasers, to realize the measurement of the surface topography with large discontinuity. In this paper, the white light source, with a single-chip CCD color camera, is used to accomplish multi-wavelength phase-shifting interferometry. In addition, we propose an algorithm which combines white light phase-shifting algorithm, equivalent wavelength method and fringe order method to achieve measuring and calibrating the micro-structures ranging from nanometer scale to micrometer scale. Finally, the proposed method is validated by a traceable step height standard.     

Dispersion-insensitive low-coherent pulses emerging from nonlinear polarization switching

We have experimentally investigated low-repetition nanosecond pulses delivered from an erbium-doped fiber (EDF) laser operating in ultra-large anomalous dispersion regime. The output pulses with rectangular profile and Gaussian spectrum almost keep invariable when they propagate through either normal- or anomalous-dispersion fibers. After nanosecond pulses are amplified via a two-stage EDF amplifier, they are broken up and exhibited as flatly broadened supercontinuum from 1520 to 1700 nm if amplified pulses are launched into a 10-km single-mode fiber, whereas the pulses retain the same duration with a broadband supercontinuum from 1200 to 1750 nm if they are input into a 100-m highly-nonlinear low-dispersion photonic-crystal fiber (PCF). The experimental observations demonstrate that the nanosecond pulses result from nonlinear polarization switching and can be regarded as dispersion-insensitive low-coherent pulses rather than compressible pulses.     

Various Trap States at SiGe-SiO2 Interface Formed by a Pulsed Laser

We report fabrication of low-dimensional structures in air by a pulsed laser on SiGe alloy samples in which different oxide structures are formed by laser irradiation and annealing treatment. The micro-structures on SiGe are more complex than those on Si. A series of photolumineseence （PL） emission is observed due to various trap states at the SiGe-SiO2 interface formed under different preparing conditions. The peak centre of PL emission exhibits red=shift from Si to SiGe because of narrower gap. A model for explaining the PL emission is proposed in which the trap states of the interface between some oxide and SiGe play an important role.     

金属塑料的研究进展

金属塑料是我国学者发现和命名的新材料.本文重点阐述金属塑料这类材料是如何发现的以及这类材料的设计思想与规则;总结了从金属塑料材料成分、典型材料的微观结构与物理化学特性等方面的最新研究成果;对于金属塑料类材料的潜在应用前景做了展望与分析.     

Comparison of supercontinuum generation based on high-energy nanosecond pulses via single-mode and photonic-crystal fibers

We have experimentally investigated the supercontinuum (SC) generation based on high-energy Gaussian-spectrum pulses emitted from an erbium-doped fiber laser with large-anomalous dispersion. The pulses exhibit rectangular shape in temporal domain with the pulse duration of about 16 ns. When the amplified pulses propagate through 10-km single-mode fiber, the SC ranged from 1530 to 1750 nm arises from the stimulated-Raman-scattering effect and the pulses break up due to the modulation instability. Comparatively, when the amplified pulses propagate through a segment of highly-nonlinear zero-dispersion-flattened photonic crystal fiber, super-broad SC beyond the range of 1300–1750 nm is generated due to strong four-wave mixing effect, whereas the pulses almost maintain their shapes.     

单冰晶石微结构与拉曼光谱特征研究

本文以单冰晶石中的AlF4-基本结构单元为基础,构建了系列团簇,采用Restricted Hatree-Fock(RHF)量子化学自洽场方法和6-31G(d)基组对团簇进行优化,并在相同的方法和基组条件下计算分子振动频率及其拉曼活性,证实AlF4-结构中Al-F键的对称伸缩振动峰位在622cm-1附近。同时,用高温拉曼光谱仪原位实测了单冰晶石成分的物质及其熔体的常温和高温拉曼光谱,研究表明,在升温过程中有单冰晶石相生成,此外,分析了其结构及其振动光谱随温度的变化。     

All-optical control of the carrier-envelope phase with multi-stage optical parametric amplifiers verified with spectral interference

Intense ultrashort laser pulses with stabilized carrier-envelope phase (CEP) are generated at 800 nm by using multi-stage collinear and non-collinear optical parametric amplifiers (OPAs). The first-stage collinear OPA is directly pumped by the fundamental-wave pulses and tuned to generate idler pulses at 1600 nm, which are further amplified by a second-stage collinear OPA, and then frequency-doubled to generate CEP-stabilized pulses at 800 nm. A non-collinear OPA is used to amplify the CEP-stabilized pulses at 800 nm. The combination of different OPAs can generate and amplify CEP-stabilized pulses at 800 nm without any detrimental influence from the fundamental-wave pulses. The CEP stabilization is verified with a simple and robust spectral interference setup. The stable interference pattern is measured for every single pulse and compared with the unstable pattern from pulses of random CEP. PACS 42.65.Re; 42.65.Yj; 42.25.Kb