可编程的多波形脉冲低温等离子电源北大核心CSCD

高压脉冲已经运用于许多领域,其中一个就是可以用来产生等离子体电源。脉冲输出参数是脉冲波形、脉冲电压幅度、脉冲频率以及脉冲持续时间等。本文应用现代电力电子技术提出了一种脉冲电路的拓扑结构,通过一定的控制算法可以产生不同的脉冲波形且脉冲幅度可以成倍增加以输出高压脉冲,并开发出了一套可编程的脉冲输出设备以用于生物组织或者材料等的改性加工。电路拓扑采用电容、二极管及开关管配合的方式工作,控制算法由复杂可编程逻辑器件FPGA来实现,通过导通或者关闭开关管来控制电容的充电或者放电以形成脉冲波形。电路拓扑通过Saber仿真软件和实测波形图证实了其可行性。通过单脉冲和多波形脉冲在生物组织上的实验对比,反应了多波形脉冲能够更好的对生物组织进行消融处理。     

可编程的多波形脉冲低温等离子电源

高压脉冲已经运用于许多领域,其中一个就是可以用来产生等离子体电源。脉冲输出参数是脉冲波形、脉冲电压幅度、脉冲频率以及脉冲持续时间等。本文应用现代电力电子技术提出了一种脉冲电路的拓扑结构,通过一定的控制算法可以产生不同的脉冲波形且脉冲幅度可以成倍增加以输出高压脉冲,并开发出了一套可编程的脉冲输出设备以用于生物组织或者材料等的改性加工。电路拓扑采用电容、二极管及开关管配合的方式工作,控制算法由复杂可编程逻辑器件FPGA来实现,通过导通或者关闭开关管来控制电容的充电或者放电以形成脉冲波形。电路拓扑通过Saber仿真软件和实测波形图证实了其可行性。通过单脉冲和多波形脉冲在生物组织上的实验对比,反应了多波形脉冲能够更好的对生物组织进行消融处理。     

气体脉冲压力的激光干涉法测量

对气体动态压力的非接触测量和溯源方法进行了研究。研制了基于激光干涉法测量气体脉冲压力的实验装置,通过光程与压力关系计算分析出气体脉冲压力的幅值和脉宽。建立了动态压力测量模型,并对测量不确定度进行了分析。开展了气体脉冲压力激光干涉测量实验,使用动态压力传感器和激光器进行同步测量,激光干涉法测量结果偏差较小,验证了装置测量的准确性。结果表明：本装置产生的脉冲压力信号稳定可靠,光学测量信号准确度高,具有实时性、非接触、可溯源等优点,可实现气体脉冲压力的测量,装置测量结果的相对标准偏差小于0.8%,测量结果的不确定度小于2%(k=2)。     

TEA CO_2激光器中均匀脉冲放电预电离条件的研究

在TEACO2激光器中，由于气压高，很容易形成弧光放电，导致激光作用停止，因此采用预电离技术是十分重要的。在已取得研究成果的基础上，通过考虑电压上升时间产生的影响，分三种情形对TEACO2激光器中均匀脉冲放电的预电离条件进行了研究，确定了预电离电子密度和最大起始极间场强的允许取值范围。对于电极间加上脉冲高压前预电离就已结束的情形，确定了电压上升时间的最大允许值。     

飞秒激光烧蚀材料表面产生纳米波纹结构的实验

利用飞秒脉冲激光烧蚀可以获得远小于激光中心波长（775nm）量级的周期条纹．通过多脉冲飞秒激光烧蚀Ni、Al、Cu、Ti和Si等材料表面的实验,得到材料表面产生光栅的周期均小于飞秒激光中心波长;采用对比实验,改变入射光的偏振特性,发现波纹周期方向随入射光偏振方向的改变而改变;不改变激光偏振态、脉冲能量为4．2J／cm^2时,沿波纹周期走向,发现平台移动速度为0．1mm／s时,可获得清晰的551nm的金属周期结构;最后应用上述实验结果,在铜片表面制备了长为几十微米、周期为551nm的微纳光栅结构。     

TEA CO2激光器中均匀脉冲放电预电离条件的研究

在ＴＥＡ ＣＯ２激光器中，由于气压高，很容易形成弧光放电，导致激光作用停止，因此采用预电离技术是十分重要的。在已取得研究成果的基础上，通过考虑电压眩升时间产生的影响，分三种情形对ＴＥＡＣＯ２激光器中均匀脉冲放电的预电离条件进行了研究，确定了预电离电子密度和最大起始极间场强的允许取值范围，对于电极间加上脉冲高压前预电离就已结束的情形，确定了电压上升时间的最大允许值。     

自变频激光晶体Nd3+:GdAl3(BO3)4的研究

采用熔盐法生长出尺寸为30mm的Nd3+:GdAl3(BO3)4优质晶体,进行了吸收光谱和荧光光谱的测定研究,计算得到晶体发射截面为σe1061.9=2.9×10-19cm2和σe1338mm=5.5×10-20cm2.采用染料激光器作为泵浦源,对晶体进行了自变频激光实验研究,在紫外可调谐(378-382nm)、绿光531nm、蓝光(436-443nm)、红光(669nm)和红外可调谐(1305-1365nm)波段实现了激光输出,输出的最大功率分别为:105μJ/脉冲、119.5μJ/脉冲、445μJ/脉冲、19μJ/脉冲和31μJ/脉冲.     

纳秒脉冲激光对316L不锈钢微抛光效果的影响

激光微抛光过程中,激光的能量密度对微抛光效果的影响很大.采用纳秒紫外脉冲激光(波长为355 nm,脉冲宽度为35 ns)对316L不锈钢材料进行微抛光实验研究,分析了工件表面的形貌、扫描速度和离焦距离等因素对激光微抛光效果的影响.通过对4种不同表面形貌的抛光效果比较,发现不仅表面粗糙度会影响抛光质量,而且表面的形貌也对激光微抛光的效果有很大影响;激光微抛光时对确定的激光能量密度存在最佳微抛光效果的扫描速度和离焦距离.提出了355 nm紫外纳秒脉冲激光器对316L不锈钢微抛光效果的最佳工艺参数:激光能量密度为0.14 J/cm2,激光脉冲重复频率为20 Hz,扫描速度为18.6 mm/min,离焦距离为81.2μm.在此工艺参数下,316L不锈钢经过微抛光之后,表面粗糙度由123.23 nm降低至80.96 nm.     

激光雷管的研究

1 引言通过对激光起爆炸药的研究,已报道了使用Q开关脉冲激光,在10ns的短时间内,照射大能量的脉冲激光,由于激光爆炸能的输入而产生冲击波起爆炸药的例子。     

连续/脉冲激光再制造FeCrNiCu合金成形层温度场研究

采用非接触式红外高温测试仪对连续/脉冲激光成形两种模式下激光再制造FeCrNiCu合金成形层温度场进行分析,获取了熔池及热影响区温度场分布的一般规律,验证了脉冲激光工艺在控制热输入和成形形变以及降低熔池及热影响区温度方面的工艺优越性。结果表明:脉冲激光成形热影响区峰值温度为730.4~810.5℃,熔池峰值温度为998.7~1383.4℃,明显低于相同工艺下连续输出模式;脉冲激光成形层具有更快的升温及降温速率,利于形成细晶组织和获得良好的力学性能;实际成形实验也进一步验证脉冲激光工艺具有更小的热影响区范围。     

Nanopatterning with interferometric lithography using a compact /spl lambda/=46.9-nm laser

We report the imprinting of nanometer-scale gratings by interferometric lithography at /spl lambda/=46.9 nm using an Ne-like Ar capillary discharge laser. Gratings with periods as small as 55 nm were imprinted on poly-methyl methacrylate using a Lloyd's mirror interferometer. This first demonstration of nanopatterning using an extreme ultraviolet (EUV) laser illustrates the potential of compact EUV lasers in nanotechnology applications.     

A Gigawatt High-Voltage Generator for Coherent Soft X-Ray Generation

A fast gigawatt high-voltage generator was developed to drive an argon-filled capillary for the generation of pulses of coherent short wavelength radiation in the extreme ultraviolet and soft X-ray region. A four-stage double Marx bank that is capable of delivering voltage pulses of 150 to 350 kV at 290-ns transition duration was used to pulse charge a 5-Omega-impedance water-filled pulse-forming line. A fast current pulse with amplitude ranging from 9 to 21 kA and 35-ns transition duration was generated through a 20-cm-long and 3-mm-diameter alumina channel filled with argon. Laser emissions in the Ne-like Ar at 46.9 nm have been observed in the pressure range of 0.14-0.38 mbar. It was also observed that over the spectral range from 20 to 70 nm, no other transitions, except the 46.9-nm line, experienced high gain and strong amplification.     

Short-pulse Injection-locking of a Mercury Chloride Laser

Abstract

We report the injection locking of a mercury chloride discharge laser. This has been achieved using an injection pulse much shorter than the slave pulse duration. Selective enhancement of HgCl laser output at wavelengths to the blue of the usual 558 nm lasing region has been observed. Mercury metastables, produced in the discharge, are found to have an absorption line coincident with an HgCl gain peak at 547 nm, and laser action at this wavelength is inhibited. This absorption has been counteracted by correctly timing the entry of the injected pulse into the slave laser cavity.     

Simultaneous quantification of etoposide and etoposide phosphate in human plasma by capillary electrophoresis using laser-induced native fluorescence detection

A method using capillary electrophoresis with UV laser-induced native fluorescence detection was developed as a sensitive and selective assay for the simultaneous determination of etoposide and etoposide phosphate in human plasma. Laser-induced native fluorescence detection with a frequency-doubled argon ion laser at an excitation wavelength of 257 nm was used for the simultaneous assay of etoposide and etoposide phosphate in plasma to improve the sensitivity compared to that obtained with UV absorption. The detection system consists of an imaging spectrograph and an intensified CCD camera which views an illuminated 1.5-mm section of the capillary. This setup is able to record the whole emission spectra of the analytes to achieve additional wavelength-resolved electropherograms. In the concentration range of 200 microg/L-50 mg/L in plasma for etoposide and 100 microg/L-20 mg/L for etoposide phosphate, coefficients of correlation were better than 0.998. Within-day variation determined with three different concentrations showed accuracies ranging from 91.0 to 109.3% for etoposide and from 91.2 to 109.9% for etoposide phosphate (n = 6) with a precision of about 8%. Day-to-day variation presented accuracies ranging from 91.8 to 107.9% for etoposide and from 94.4 to 109.3% for etoposide phosphate with a relative standard deviation less than 6% (n = 5). To our knowledge, this is the first method for the simultaneous quantification of etoposide and etoposide phosphate in plasma samples.     

交流量热法测量SiO2薄膜的热扩散率

介绍了交流量热法测量薄膜热扩散率的原理和系统组建，用脉宽为纳秒级的超短激光脉冲作为热源，测量了Si衬底上厚度为100nm和500nm的SiO2薄膜水平方向上的热扩散率，实验结果表明该结构的热扩散率比SiO2体材料的要小，并且随着SiO2层厚度的减小，热扩散率也减少。     

Modulated laser source for monitoring the stability of detectors employing photomultipliers

Light from an argon high stability laser is used together with an acoustic-optic modulator to provide constant energy calibration pulses to the photomultiplier tubes in an experimental setup. This solution is proposed as the most appropriate when many (up to one/two hundred) of PMTs must be monitored and controlled for gain stability. In our case, gain changes should be limited to 1% which means a still better reproducibility for both the intensity and the width of the calibrator light pulses. In this paper we motivate our choice, present a simple crystal controlled pulse generator which assures the required long-term width stability and give the results obtained in several experimental runs.     

Dust particle formation in low pressure Ar/CH4 and Ar/C2H2 discharges used for thin film deposition

This paper deals with the study of the temporal and spatial evolution of the dust formation in two types of capacitively coupled discharges in Ar/C₂H₂ and Ar/CH₄ gas mixtures used for thin film deposition. To initiate the particle growth in the Ar/CH₄ discharge it is necessary either to apply transiently high power to the discharge or to inject transiently a pulse of C₂H₂. In the Ar/C₂H₂ discharge, however, the particles are formed spontaneously at constant low power. Due to the different initiation process the further temporal evolution of the dust formation is significantly different for both kind of gas mixtures. In the case of argon/acetylene the formation of dust particles shows a periodical behavior, which is not observed in the argon/methane mixture. The dust particles are detected by means of laser light scattering and by measuring the extinction of the laser after passing the discharge. The chemical nature of the particles was studied in situ by means of a multi pass FTIR-spectrometer. The thin film deposition was measured with an in situ ellipsometer.     

Effect of voltage and capacitance in nanosecond pulse discharge enhanced laser-induced breakdown spectroscopy

The laser ablation fast pulse discharge plasma spectroscopy (LA-FPDPS) technique has demonstrated its validity to enhance the optical emission of laser-induced plasma. It has the potential to improve the performance of traditional LIBS measurement. Very recently, LA-FPDPS with a nanosecond pulse discharge circuit has been developed, which has a better capability to enhance the optical emission intensity of laser plasma compared with that using a microsecond pulse discharge circuit. In this paper, the effect of the discharge capacitance and discharge voltage on the optical emission of soil plasma generated by LA-FPDPS with a nanosecond pulse discharge circuit is evaluated in detail. In addition, the stability of the time delay between the laser firing and discharge, and between the discharge and optical emission, has been carefully investigated.     

Development of a detector for ultratrace nitrogen in argon using low-pressure, capillary glow discharge molecular emission spectrophotometry

A highly sensitive detector was developed for determining parts per billion of nitrogen in high-purity argon. The method is based on the spectrophotometric determination of the emission intensity from the nitrogen molecule excited in the lowest vibrational transitions of the electronic C(3)Π(u) → B(3)Π(g) system. A capillary glow discharge technique was applied to excite nitrogen in an argon flow at several Torr. The low-pressure, capillary glow discharge method offered high sensitivity for detecting trace nitrogen in argon. The response of the detector was proportional in the range of nitrogen concentrations from 0.1 ppb, which correspond to S/N = 3, to 100 ppm.     

Analysis of 1ω bulk laser damage in KDP

The influence of laser parameters on laser-induced damage in the bulk of KDP is difficult to determine because the damage manifests as discrete sites a few micrometers in diameter distributed throughout a relatively large volume of material. Here, we present a method to directly measure the size and location of many thousands of such sites and correlate them to the laser conditions that produced them. This technique is used to characterize the effects of pulse duration on damage initiated by 1053?nm light in the bulk of KDP crystals. We find that the density of damage sites produced by 1053?nm light is less sensitive to pulse duration than was previously reported for 526?nm and 351?nm light. In addition, the effect of pulse duration on the size of the damage sites produced appears insensitive to wavelength.