激光驱动飞片超高速发射技术实验研究

 介绍了影响激光驱动超高速发射技术的各种因素。分析了激光能量、激光光束空间分布对飞片发射速度及完整性的影响和飞片靶镀膜工艺对飞片速度及完整性的影响。结果表明：空间分布为“平顶型”的激光束有利于发射出完整的飞片。在膜与基底之间增加过渡层Cr可以大大提高膜与基底之间的附着力,从而提高飞片的发射速度。实验上利用波长1 064 nm、脉宽10 ns、能量835 mJ的激光使厚度5 μm、直径1 mm的铝飞片的发射速度达到10.4 km/s。大大提升了对微米级空间碎片速度的发射能力。     

光纤传输激光驱动飞片实验研究

构建了一种基于光纤传输高功率激光的飞片发射系统,并测试了飞片速度.飞片膜层为三明治结构:铝烧蚀层、氧化铝隔离层和铝飞片产生层.飞片膜层采用磁控溅射技术沉积在玻璃衬底上,总厚度为5.5 μm.激光辐照铝膜层产生高温高压等离子体,驱动剩余膜层产生高速飞片,速度达数km/s.同时,实验研究了光纤传能系统的输出激光空间分布特性和传输激光能量容量,它们决定了飞片的平面性和最大速度.光纤端面损伤是限制光纤传输激光能量容量的关键因素,光纤端面通过精密机械抛光和激光预处理可以获得理想的抗激光损伤能力.采用基于光纤阵列探针的时间序列测试技术获得了飞片的平均速度,并评估了飞片的平面性.采用搭建的基于光纤传输高功率激光的飞片发射系统获得了速度达1.7 km/s、直径接近1 mm的高速飞片. 关键词： 激光驱动飞片 激光辐照 光纤阵列探针 激光等离子体     

激光驱动飞片过程中激光烧蚀深度的计算

利用激光体烧蚀模型,数值模拟了激光驱动飞片的加速过程,包括激光的吸收和飞片的速度历史等。在光强为GW/cm2量级的激光作用下,激光烧蚀产生的等离子体的流体力学运动可用改编的1维La-grange流体力学计算程序SSS来描述。通过计算得到不同激光能量下的飞片密度剖面,由此给出金属薄膜的烧蚀深度与实验测量值进行比对,二者符合得较好。     

Feasibility investigations on a novel micro-embossing using laser-driven flyer

A novel micro-plastic microfabrication technique for embossing is presented, which uses laser-driven flyer as the loading method in forming. Experiments were performed by allowing the laser-driven flyer to impact the thin film, which is placed above a micromold. Micro-channel with dimension of 160 μm×45 μm was successfully fabricated on copper foil surface using laser-driven flyer. The effects of laser energy on deformation mechanism were investigated experimentally. Surface roughness changes on formed sample were discussed. The novel technique holds promise for achieving precise, well-controlled, low-cost, high efficiency of three-dimensional metallic microstructures. In addition, this technique can cold form high strength or difficult materials.     

基于聚龙一号装置的超高速飞片发射实验研究进展

磁驱动加载技术通过脉冲功率源将超大脉冲电流加载到实验负载区,从而形成随时间平滑上升的磁压力,实现对样品的准等熵压缩和超高速飞片发射.本文基于聚龙一号装置的输出特性参数,依次从负载结构、电极尺寸、电流波形和诊断系统等方面,分别设计完成了两种负载构型的超高速飞片发射实验.其中应用单侧带状负载发射尺寸Φ10 mm×0.725 mm的LY12铝飞片速度达到11.5 km/s,磁驱动加载压力近0.9 Mbar.比较模拟计算与实验结果,飞片发射过程和最终速度基本一致.而进一步的模拟计算表明,优化的负载结构尺寸和电流波形调节方案下,将有望发射尺寸Φ8.5 mm×1 mm的铝飞片速度超过15 km/s.从模拟设计到实验开展,已初步掌握了基于多支路脉冲功率发生器的超高速飞片发射实验技术.     

细光束在钝锥体外流场中的追迹

飞行的钝锥体外流场在密度分布上具有强烈非均匀性,这将导致其传输的细光束在远场靶面上产生偏移,从而影响其光学探测系统的作用精度。探讨并给出了任意折射率分布介质中的光线追迹方法。利用该方法对钝锥体外流场中的细光束路径进行了计算。计算结果表明：在所选位置上,锥体外流场对光线的出射角有明显的影响,但不是特别剧烈;当钝锥体表面加冷却源后,流场密度梯度变化加大,光束出射角的脱靶量明显加大。校正外流场为分析钝锥体上光学系统引入的目标脱靶量提供参考依据。     

激光驱动飞片加速特征分析

在激光驱动飞片研究中,飞片的加速特征是需要认识的关键问题之一。设计了强激光作用金属膜驱动飞片实验,采用聚偏氟乙烯（PVDF）压电薄膜测量了飞片到达不同距离的时间,计算得到飞片速度和加速度,分析激光能量对飞片加速性能的影响。基于Gurney能理论,建立了激光驱动飞片速度的计算模型,根据实验结果获得了激光能量损失系数和有效吸收系数,分析了激光能量和膜体厚度对飞片速度的影响。实验结果表明:不同激光能量下飞片的加速特征基本相似,激光能量变化对飞片的加速时间影响较小; 激光能量较大的情况下,膜体厚度对飞片最大速度、能量耦合系数的影响更显著; 当膜体超过一定厚度时,能量耦合系数不再增加。     

Large area laser surface micro/nanopatterning by contact microsphere lens arrays

Laser surface micro/nanopatterning by particle lens arrays is a well-known technique. Enhanced optical fields can be achieved on a substrate when a laser beam passes through a self-assembled monolayer of silica microspheres placed on the substrate. This enhanced optical field is responsible for ablative material removal from the substrate resulting in a patterned surface. Because of the laser ablation, the microspheres are often ejected from the substrate during laser irradiation. This is a major issue impeding this technique to be used for large area texturing. We explored the possibility to retain the spheres on the substrate surface during laser irradiation. A picosecond laser system (wavelength of 515 nm, pulse duration 6.7 ps, repetition rate 400 kHz) was employed to write patterns through the lens array on a silicon substrate. In this experimental study, the pulse energy was found to be a key factor to realize surface patterning and retain the spheres during the process. When the laser pulse energy is set within the process window, the microspheres stay on the substrate during and after laser irradiation. Periodic patterns of nanoholes can be textured on the substrate surface. The spacing between the nanoholes is determined by the diameter of the microspheres. The depth of the nanoholes varies, depending on the number of laser pulses applied and pulse energy. Large area texturing can be made using overlapping pulses obtained through laser beam scanning.     

小型激光器驱动飞片的平均速度测量研究

 提出了一种小型激光器驱动飞片的平均速度测量方法,即利用石英晶体的压电效应可以最终得到飞片的平均速度。详细介绍了激光驱动飞片的过程,石英计的设计等,对系统的响应灵敏度和实验数据进行了分析,结果显示：这一方法具有简单可靠的特点,可以在一定程度上满足实验精度的要求。     

Generation of laser-driven flyer dominated by shock-induced shear bands: A molecular dynamics simulation study

High-power pulsed lasers provide an ingenious method for launching metal foils to generate high-speed flyers for high-pressure loading in material science or aerospace engineering.At high-temperature and high-pressure laser-induced conditions,the dynamic response of the metals and the mechanism of flyer formation remain unclear.In this study,the overall process of the laser-driven aluminum flyer,including laser ablation,rupture of metal foil,and the generation of the flyer was investigated by molecular dynamics combined with the two-temperature model.It was found that under high laser fluence(over 1.3 J/cm;with 200-fs laser pulse duration),the laser induced a shock wave with a peak pressure higher than25 GPa,which led to shear bands expanding from the edge of the laser ablation zone in the foil.Compared with the cases of low laser fluence less than 0.5 J/cm^-1,the shear band induced by high laser fluence promotes the rupture of the foil and results in a high-speed flyer(>1 km/s)with better flatness and integrity.In addition,the shock wavefront was found to be accompanied by aluminum crystal phase transformation from face-centered cubic(FCC)to body-centered cubic structure.The crystal structure reverts with the decrease of pressure,therefore the internal structure of the generated flyer is pure of FCC.The results of this study provide a better understanding of the laser-induced shock effect on the foil rupture and flyer quality and forward the development of the laser-driven flyer.     

Laser-driven flyer application in thin film dissimilar materials welding and spalling

This paper applied a low cost method to pack and drive laser-driven flyer in the applications of welding and spalling. The laser system has the maximum energy of 3.1 J, which is much lower than that used in the previous study. The chemical release energy from the ablative layer was estimated as 3.7 J. The flying characteristic of laser-driven flyer was studied by measuring the flyer velocity at different locations with photonic Doppler velocimetry (PDV). The application of laser-driven flyer in welding Al and Cu was investigated at different laser spot size. Weld strength was measured with the peel test. Weld interface was characterized with optical microscopy (OM) and scanning electron microscopy (SEM). The study of application of laser-driven flyer in spalling was carried out for both brittle and ductile materials. The impact pressure was calculated based on the Hugoniot data. The amount of spalling was not only related to the impact pressure but also related to the duration of impact pressure. The fractography of spalled fracture surface was studied and revealed that the fracture mode was related to the strain rate. The spall strength of Cu 110, Al 1100 and Ni 201was measured and was consistent with the literature data.     

用于激光驱动飞片诊断的线成像速度干涉仪

设计并建立了一套完整的线成像激光干涉测速系统,用于激光驱动技术中小尺寸飞片或样品一条线上所有点的速度测量。它将激光压缩为线状照射到靶面,用成像物镜收集靶面的漫反射光并传递到广角迈克尔逊干涉腔中形成干涉,产生的梳妆干涉条纹作为信号载体,用变像管扫描相机记录条纹随时间的变化,用不同位置的条纹移动量反推出不同位置的速度分布,实现空间分辨。系统具有50 ps响应时间和20μm空间分辨能力。用该系统测量了激光驱动飞片的速度场,清晰的扫描干涉图像直观显示了飞片的运动过程和各点的速度差异。用傅里叶变换方法对干涉图像进行处理,得到了靶面一条线的速度和位移分布。     

Cerium oxide nanoparticles protect primary mouse bone marrow stromal cells from apoptosis induced by oxidative stress

The sintering of a silver (Ag) nanoparticle film by laser beam irradiation was studied using a CW DPSS laser. The laser sintering of the Ag nanoparticle thin film gave a transparent conductive film with a thickness of ca. 10 nm, whereas a thin film sintered by conventional heat treatment using an electronic furnace was an insulator because of the formation of isolated silver grains during the slow heating process. The laser sintering of the Ag nanoparticle thin film gave a unique conductive network structure due to the rapid heating and quenching process caused by laser beam scanning. The influences of the laser sintering conditions such as laser scan speed on the conductivity and the transparency were studied. With the increase of scan speed from 0.50 to 5.00 mm/s, the surface resistivity remarkably decreased from 4.45 × 10⁸ to 6.30 Ω/sq. The addition of copper (Cu) nanoparticles to silver thin film was also studied to improve the homogeneity of the film and the conductivity due to the interaction between the oxidized surface of Cu nanoparticle and a glass substrate. By adding 5 wt% Cu nanoparticles to the Ag thin film, the surface resistivity improved to 2.40 Ω/sq.     

“聚龙一号”装置上磁驱动铝飞片实验的数值模拟

采用二维磁驱动数值模拟程序MDSC2,对大电流脉冲装置"聚龙一号"上的151发次磁驱动370μm厚铝飞片实验、164发次磁驱动330μm厚铝飞片实验进行了数值模拟和分析。数值模拟表明:370μm厚铝飞片和330μm厚铝飞片的磁驱动过程中,VISAR测量的速度不是飞片自由面的速度,而是飞片中邻近自由面最近的固体反射面的速度。这是由于磁驱动飞片发射过程中,飞片自由面部分被烧蚀,密度低于固体密度状态,而飞片自由面和加载面中间的飞片还保持固体密度状态。VISAR测量的激光将穿过自由面的低于固体密度状态的飞片部分,到达飞片自由面最近的固体密度位置再反射回去,获得这一位置的飞片速度。数值模拟的飞片固体反射面速度历史和VISAR测量的速度历史相吻合。     

Mid-infrared fiber-coupled QCL-QEPAS sensor

An innovative spectroscopic system based on an external cavity quantum cascade laser (EC-QCL) coupled with a mid-infrared (mid-IR) fiber and quartz enhanced photoacoustic spectroscopy (QEPAS) is described. SF₆ has been selected as a target gas in demonstration of the system for trace gas sensing. Single mode laser delivery through the prongs of the quartz tuning fork has been obtained employing a hollow waveguide fiber with inner silver–silver iodine (Ag–AgI) coatings and internal core diameter of 300 μm. A detailed design and realization of the QCL fiber coupling and output collimator system allowed almost practically all (99.4 %) of the laser beam to be transmitted through the spectrophone module. The achieved sensitivity of the system is 50 parts per trillion in 1 s, corresponding to a record for QEPAS normalized noise-equivalent absorption of 2.7 × 10^?10 W cm^?1 Hz^?1/2.     

Laser-induced fabrication of randomly distributed nanostructures in fused silica surfaces

The nanostructuring of dielectrics is a big challenge for laser patterning methods. In this study a novel laser structuring method for the fabrication of randomly distributed nanostructures, called laser-induced front side etching using in situ pre-structured metal layers (IPSM-LIFE), is presented. The pulsed laser irradiation of a thin metal film deposited onto a dielectric substrate with fluences below the ablation threshold results in the formation of randomly distributed metal structures by self-assembly processes. Further pulsed laser irradiation of these metal structures with higher or equal laser fluences causes the formation of complex patterns at the surface of the dielectric due to localized ablation and melting processes of the dielectric surface induced by the absorption of the laser energy by the metal structures and the local energy transfer into the dielectric surface. The pattern formation observed in the film and the dielectrics substrate after irradiation of 10 nm chromium layers on fused silica, with laser pulses (Δt _p =25 ns, λ=248 nm), was studied by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Different features with a lateral size down to a few tens of nanometers, like concentric ring patterns, donut-like structures, and bar patterns were observed at the dielectric.     

激光驱动飞片的线面成像VISAR测速技术

以激光驱动飞片速度场诊断为例,展示线面同时成像任意反射面速度干涉仪(VISAR)技术在超高速碰撞研究中的应用前景。将传统VISAR改为成像干涉结构,用变像管扫描相机和高速光电分幅相机分别记录作为信号载体的梳状干涉条纹随时间的变化,实现靶面一条线上各点速度历程和多个时刻二维靶面上所有点速度相对分布的测量。所研制的线面同时成像VISAR具有10μm的空间分辨和约15m/s的速度分辨能力。用其测量了激光驱动铝膜飞片的速度场,直观给出飞片的演化发展过程。实验结果表明,线面同时成像VISAR技术可以为激光驱动飞片、超高速碰撞等领域的理论研究和数值模拟提供有效比对实验数据。     

自由面被烧蚀磁驱动飞片的数值模拟

为了理解磁驱动飞片自由面烧蚀的机理、自由面被烧蚀后飞片的物质状态、自由面被烧蚀后激光速度干涉仪(VISAR)测量的机理等,采用磁驱动数值模拟程序MDSC2对聚龙一号装置上PTS-151发次磁驱动飞片实验中370 m厚飞片进行了模拟和分析。数值模拟表明,334 ns之前飞片自由面部分保持固体状态,334 ns之后飞片自由面部分已经熔化,到340 ns后整个飞片都被熔化。飞片自由面烧蚀的主要机制是电流焦耳加热,热扩散和压缩做功的贡献很小。数值模拟的固体密度反射面速度历史和VISAR测量的速度历史一致。飞片自由面熔化后,VISAR测量的速度是距离自由面最近的固体密度反射面的速度。     

Proposed electrically-pumped,III–V-metal hybrid plasmonic lasers

We propose an electrically-pumped hybrid plasmonic laser through the integration of a semiconductor quantum well laser with a thin metal film. Due to the coupling between the TM waveguide mode in the III–V active layer and the LRSPP mode around the metal thin film, light can be confined in both regions and optical gain can be provided by the active layer. We have shown that the quasi-odd supermode is the preferred lasing mode because of its larger confinement factor and lower modal loss compared to the quasi-even supermode. Through optimizing the gap distance between the active region and the metal film, we can obtain low threshold and a large amount of optical energy confined around the metal film for the hybrid plasmonic laser.     

High frequency impedance spectroscopy study on Gd-doped CeO<Subscript>2</Subscript> thin films

The gadolinia-doped ceria (GDC) thin films were deposited by pulsed laser deposition. Samples with special geometry were prepared which allowed us to characterize GDC film in across-plane direction. The electrical properties of the films were investigated by means of impedance spectroscopy in the frequency range of 10 Hz to 10 GHz and 380–600 K temperature interval. The data analysis was performed by using appropriate equivalent circuit. The equivalent circuit modeled thin GDC film itself, platinum metal connections (traces) in the dielectric medium of sapphire substrate and interfaces between the film and platinum electrodes. Hence, several factors influenced the impedance spectra, namely the properties of substrate, the oxygen-ion transport in the film, ion blocking at the interface between the film and the electrode, and metal traces. The electrical properties of GDC thin films were compared with these of bulk ceramics and showed similar conductivity and dielectric permittivity values. The study also revealed that measurement data at electrical field frequencies of up to 10 GHz were particularly important to correctly estimate electrical properties of GDC thin films, because at high temperatures the electric response of GDC film shifts to high frequencies (higher than 1 MHz at 600 K). The thin film sample preparation for high frequency measurements and fitting of impedance data by using relatively simple equivalent circuit model is presented.