基于脉冲CO2激光锡等离子体光刻光源的极紫外辐射光谱特性研究

研究了不同条件下脉冲放电CO₂激光烧蚀平板锡靶产生的等离子体极紫外辐射特性, 设计并建立了一套掠入射极紫外平焦场光栅光谱仪, 结合X射线CCD探测了光源在6.5～16.8 nm波段的时间积分辐射光谱,得到了极紫外光谱随激光脉宽, 入射脉冲能量及背景气压的变化规律。实验结果发现：入射激光脉冲能量在30～600 mJ变化时,极紫外辐射光谱的强度随辐照激光脉冲能量的增加而增加, 但并不是线性关系, 具有饱和效应, 且产生极紫外辐射的脉冲能量阈值约为30 mJ,当激光脉冲能量为425 mJ时具有最高的转换效率,此时中心波长13.5 nm处2%带宽内的转换效率约为1.2%。激光脉冲半高全宽在50～120 ns范围内变化时, 极紫外辐射光谱的峰值位置均位于13.5 nm,光谱形状几乎没有什么变化, 但是脉宽从120 ns变到52 ns后,由于激光功率密度的提高,极紫外辐射强度也随之增强了约1.6倍。极紫外光谱的强度随背景气压的增大而迅速下降, 当腔内空气气压为200 Pa时, 极紫外辐射光子几乎被全部吸收,而当缓冲氦气气压为7×104 Pa时,仍能够探测到微弱的极紫外辐射信号,计算表明100 Pa的空气对13.5 nm极紫外光的吸收系数为3.0 m-1,而100 Pa的He气的吸收系数为0.96 m-1。     

Radiative Characteristics of Shock-Heated Oxygen

Journal of Applied Spectroscopy - The emission spectra of oxygen behind the front of a strong shock wave were studied in the range of shock wave speeds of 5.7–7.4 and 8.1–10.0 km/s at...     

Study of the absorption characteristics of molecular oxygen in the Schumann-Runge system at high temperatures: I. Calculations of absorption spectra

A program for calculating the absorption and emission spectra of diatomic molecules that can take into account the vibrational-rotational interaction and nonequilibrium conditions of the gaseous medium is created. The program also allows one to perform calculations for a particular experimental setup by specifying the corresponding instrumental function. The absorption cross sections of molecular oxygen are calculated in the Schumann-Runge system for the temperature range 1000–6000 K and the wavelength interval 130–280 nm. These calculations are compared with the experimental data obtained behind the shock wave front in oxygen-argon mixture at different temperatures for a number of wavelengths in the range of 160–270 nm.     

空气电晕放电发展过程的特征发射光谱分析与放电识别

局部空气放电是导致高压输变电设备绝缘劣化的重要因素。空气放电中丰富的发射光谱信息与放电特征存在直接映射关系。采用针-板电极模拟了空气电晕放电的发展过程,并检测了放电由弱变强过程中的“紫外-可见光-近红外”波段在200～980 nm范围内的发射光谱。放电初期的发射光谱主要由氮气分子N₂的带状光谱组成,分别为N₂第二正带系(second positive system, SPS)和N₂第一正带系(first positive system, FPS)。放电程度加深后,发生能级跃迁的粒子种类更加丰富,由此产生了带状光谱与线状光谱相互交叠的复杂谱线,光谱范围也由放电初期的280～460 nm扩展至200～980 nm。放电处于临界击穿时,发射光谱的强度急剧增加,强度最高值出现在500.715和777.202 nm处,分别对应氮离子N⁺和氧原子O的辐射谱线,这意味着微观放电过程再次发生改变。基于空气放电机理分析得到：放电初期、放电加深、放电临界击穿三个阶段中强度占优的谱峰或谱带分别由N₂...     

Shadowgraph investigation of plasma shock wave evolution from Al target under 355-nm laser ablation

The propagation of a plasma shock wave generated from an Al target surface ablated by a nanosecond Nd:YAG laser operating at 355 nm in air is investigated at the different focusing positions of the laser beam by using a time-resolved shadowgraph imaging technique. The results show that in the case of a target surface set at the off-focus position, the condition of the focal point behind or in front of the target surface greatly influences the evolution of an Al plasma shock wave, and an ionization channel forms in the case of the focal point set in front of the target surface. Moreover, it is found that the shadowgraph with the evolution time around 100 ns shows that a protrusion appears at the front tip of the shock wave if the focal point is at the target surface. In addition, the calculated results of the expanding velocity of the shock wave front, the mass density, and pressure just behind the shock wave front are presented based on the shadowgraphs.     

金纳米颗粒的紫外、蓝紫光波段光致荧光特性

采用电化学方法制备出粒径在20～30 nm的悬浮胶体金纳米颗粒。研究了金纳米颗粒的荧光发射光谱特性。在377和459 nm观察到两个荧光发射峰,分别位于紫外和蓝紫光波段,对应的敏感激发波长为220 nm。减小激发光强度或降低金纳米颗粒的粒子数密度都会使377 nm处的荧光发射峰强度减弱。位于459 nm处的荧光发射峰对激发光强度和颗粒数密度变化更为敏感,并且在激发光强度降低到一定阈值或粒子数密度高于一定阈值后消失。随着激发光强度的增加,位于377和459 nm处的两发射峰强度逐渐靠近,其比值逼近于1。实验结果与随机分布介质的自组织散射式谐振腔理论符合得较好。这表明胶体金纳米颗粒中存在循环多重散射,并由此引发了蓝光及紫外波段的荧光增强,这在光存储和全色显示等方面具有潜在的应用前景。     

Analysis of Plasmadynamic Nanosecond-Range Processes in the Formation of Shock Waves from Pulsed Discharges

We have studied the dynamics of the plasma glow of pulsed discharges (sliding surface discharge and combined volume discharge with plasma electrodes) in the nanosecond range (100–12 000 ns) in stationary air and in the flow behind the front of a plane shock wave with Mach numbers 1.7–5.0 in the shock tube channel. The temporal characteristics of the flow, the radiation spectra, and the discharge currents in air are compared in the pressure range 5–150 Torr, a pulsed voltage of 20–30 kV, and a current of about 1 kA. It is shown that the time of current under various conditions does not exceed 400 ns, and the duration of the glow can reach a few microseconds. It is shown that as a result of energy supply near the planar shock wave front, the decay of discontinuities occurs with the formation of shock waves and contact surfaces. The positions of the plasma glow regions are compared with the positions of discontinuity surfaces of numerically calculated gasdynamic parameters in the flow.     

Grid turbulence and its interaction with a shock wave

Turbulent fluctuations of density and pressure in air and argon in a shock tube have been investigated as well as their interaction with a shock wave reflected from a perforated plate at the end of a shock tube. Air and argon were used as test gases. The Mach number of the incident shock was 1.9–3.9, that one of the reflected shock was 1.4–2.4. The turbulent length scale behind the incident shock was measured as well as that one behind the reflected shock. The last value is a few times less than the former. It was established that there is overpressure in the turbulent flow behind the reflected shock. The value of the overpressure is 12% in argon and 9% in air.     

Development of gas-dynamic perturbations propagating from a distributed sliding surface discharge

Results are presented from experimental studies of the plasma layer structure of a distributed sliding surface discharge excited in quiescent air and in a uniform gas flow behind a plane shock wave at gas densities of 0.03–0.30 kg/m³. The dynamics of weak shock waves generated after discharge initiation was studied. According to the experimental and simulation results, 40% of the discharge energy transforms into heat within a surface gas layer in the energy input stage, which lasts up to 200 ns.     

入射激波诱导环氧丙烷爆炸特征研究

用自行设计激波管点火测试技术,实验研究了温度范围760-1380K间入射激波诱导下环氧丙烷的点火机理。利用激波管压力传感器测定了H*(486.1) 和O (470.5nm)随激波诱导强度变化的点火时间特征。实验结果表明：在低马赫数下氢氧自由基出现时间较接近,1.5-2.5马赫间随激波诱导强度增大而线性减小;而马赫大于2.5后,氧自由基的出现时间迅速减小,是由于高活化能的氧自由基的点火时间对强激波较敏感,而诱导强度大于3.5马赫后对两者点火影响区别就下明显了。实验数据将有益于含能材料点火时间的研究。     

入射激波诱导环氧丙烷爆炸特征研究

用自行设计激波管点火测试技术,实验研究了温度范围760-1380K间入射激波诱导下环氧丙烷的点火机理。利用激波管压力传感器测定了H*(486.1) 和O (470.5nm)随激波诱导强度变化的点火时间特征。实验结果表明：在低马赫数下氢氧自由基出现时间较接近,1.5-2.5马赫间随激波诱导强度增大而线性减小;而马赫大于2.5后,氧自由基的出现时间迅速减小,是由于高活化能的氧自由基的点火时间对强激波较敏感,而诱导强度大于3.5马赫后对两者点火影响区别就下明显了。实验数据将有益于含能材料点火时间的研究。     

Ultraviolet gas-discharge lamp on iodine molecules

The emission characteristics of a pulsed-periodic UV radiation source are reported. The source excited by a pulsed-periodic capacitive discharge initiated in helium-iodine vapor, neon-iodine vapor, or krypton-iodine vapor mixtures radiates in the spectral range 200–450 nm. It is shown that most of the plasma radiation power concentrates in the integral line of the iodine atom (206.2 nm) and in the D′-A′ band of the iodine molecule with a maximum at 342 nm. The radiation intensity of the lamp is optimized in accordance with the partial pressure of the inert gases. The discharge plasma parameters that are of interest for simulating the process kinetics and the output characteristics of an UV source based on molecular iodine, atomic iodine, and xenon iodide are calculated in helium-iodine vapor and xenon-iodine vapor mixtures.     

Dynamics of the nanosecond destruction of stressed granite during shock loading

The method of luminescence with a time resolution of 2 ns has been applied to studying the dynamics of the surface destruction of uniaxially compressed granite by a shock wave caused by electric discharge in air near its surface. The shock impact causes emission of jets of positively charged ions from the most strongly distorted regions on the sample surface. It has been discovered that, when the compressing stress reaches ~0.92–0.95 times the sample’s breaking stress, two maxima can be observed on the time dependence of the jet intensity. The first maximum corresponds to the shock wave reaching the sample surface and the second maximum corresponds to the crack destroying the sample.     

On the possibility of laboratory shock wave studies of the equation of state of a material at gigabar pressures with beams of laser-accelerated particles

The possibility of laboratory shock wave studies of the equation of state of a material with beams of laser-accelerated charged particles at pressures an order of magnitude higher than those reached in current experiments has been discussed. The possibility of the generation of a plane quasistationary shock wave with a pressure of several gigabars behind its front at the irradiation of a target by a laser beam with an energy of several kilojoules and an intensity of about 10¹⁷ W/cm², which is accompanied by the generation of fast electrons with an average energy of 20–50 keV, has been justified.     

Pressure fluctuations within a turbulent gas flow and their interaction with a shock wave

The interaction of a shock wave with a turbulent air flow is investigated experimentally. The turbulence was created with the aid of a grid. On its reflection from a perforated disc the wave propagated through a turbulent flow. The Mach number of the incident shock was equal to 1.9–4, the Mach number of the reflected wave was equal to 1.6–2.5. We found the autocorrelation functions of pressure fluctuations and their phase diagrams. The turbulent length scale of pressure fluctuations behind the incident shock was determined. The appropriate quantity behind the reflected wave is less of an order as compared with the previous case. It is established that the pressure behind the reflected wave in the turbulent flow is 7–8% higher as compared with the pressure in the laminar flow, if other conditions are the same.     

高超声速再入试验的辐射光谱定量测量

利用膨胀管对宽度为45 mm和90 mm的半圆柱模型进行了地球再入高超声速流动试验,再入速度为8 km/s。试验利用配有ICCD相机的光谱仪,测量了具有空间分辨的激波后辐射光谱,光谱范围为250~550 nm,得到了沿流体方向的激波辐射轮廓线。分析发现在该光谱范围内辐射主要为CN(B-X)带系分子光谱。利用卤钨灯对该波段光谱进行定标,得到了激波层辐射的绝对辐射亮度。通过采用两种模型辐射亮度对模型宽度归一化后发现,绕流场高温气体辐射存在较强的自吸收现象,同时观测到了绕流场激波的三维效应。通过实验发现,CN(B-X)Δv=0带系的3-3振动带系385.2 nm波长位置和0-0带系388.4 nm波长位置辐亮度之比随着流场靠近模型边缘而逐渐下降,这表明激波层内辐射的动态非平衡特征。     

Bi靶激光等离子体极紫外光源以及碎屑辐射特性研究

激光等离子体极紫外光源具有体积小、稳定性高和输出波长可调节等优势,在极紫外光刻领域发挥着重要的作用。Bi靶激光等离子体极紫外光源在波长9～17 nm范围内具有较宽的光谱,可应用于制造极紫外光刻机过程中所需的极紫外计量学领域。利用平像场光谱仪和法拉第杯对Bi靶激光等离子体极紫外光源以及离子碎屑辐射特性进行了实验研究。在单脉冲激光打靶条件下,实验中观察到Bi靶激光等离子极紫外光谱在波长12.3 nm处出现了一个明显的凹陷,其对应着Si L-edge的吸收,是Bi元素光谱的固有属性。相应地在波长为11.8和12.5 nm位置处产生了两个宽带的辐射峰。研究了两波长光谱特性以及辐射强度随激光功率密度的变化。结果表明,在改变聚焦光斑大小实现不同激光功率密度（0.7×1010～3.1×1010 W·cm-2）过程中,当功率密度为2.0×1010 W·cm-2时两波长处的光辐射最强,其原因归结为Bi靶极紫外光辐射强度受激光能量用于支撑等离子膨胀的损失和极紫外光被等离子体再吸收之间的平衡制约所致。在改变激光能量实现不同激光功率密度过程中,由于烧蚀材料和产生两波长所需高阶离子随着功率密度的增加而增加,增强了两波长处的光辐射。进一步,研究了双脉冲激光对Bi靶极紫外光谱辐射特性影响,实验发现双脉冲打靶下原来在单脉冲打靶时出现在波长13～14 nm范围内的凹陷消失。最后,对单脉冲激光作用Bi靶产生极紫外光源碎屑角分布进行了测量。结果表明,当探测方向从靶面法线方向移动到沿着靶面方向上的过程中,探测到Bi离子动能依次减小,并且离子动能随激光脉冲能量降低而呈线性减小。此项研究有望为我国在研制极紫外光刻机过程所需的计量学领域提供技术支持和打下夯实的基础。     

样品温度和空间约束两种方法相结合对激光诱导击穿光谱的影响

升高样品温度和采用空间约束能提高激光诱导击穿光谱的信号强度,两种技术的结合可以进一步提高激光诱导击穿光谱的光谱强度.本文在空气环境中研究了升高样品温度和空间约束效应两种方法相结合对激光诱导击穿光谱的影响,测量了激光诱导铝等离子体的时间分辨光谱.实验结果表明:升高样品温度能增加激光诱导击穿光谱的信号强度,高温样品能耦合更...     

Observation of nonequilibrium radiation behind strong shock waves in low-density air

Nonequilibrium radiation phenomena behind strong shock waves in low-density air are observed by using a couple of CCD camera systems in a shock tube experiment. The simultaneous observation for total radiation and its spectral radiation is carried out in order to elucidate spaced-ependent contribution of an individual radiation spectrum to the total radiation intensity. The results are shown for the shock velocity range from 9.0 km/s to 12.1 km/s at the initial pressure 13.3 Pa. Wavelength range is selected from 300 nm to 445 nm to investigate mainly the contributions from UV radiation. It is found that the band spectra due to the molecular species N₂⁺ and CN mainly contribute to the first-peak, while the spectra due to the atomic species O⁺ and N mainly contribute to the formation of the second-peak. It is also found that the Balmer series in H spectra strongly contributes to the second-peak. The radiation along the tube wall surfaces is composed of the same constituents as those around the tube axis as well as the spectra coming from the impurities.     

Oxygen spectral lines for diagnostics of atmospheric laser-induced plasmas

In the present study OI spectral lines are measured, tested, and developed for diagnostics of laser-induced plasma experiments in air. The plasma plume was generated by the interaction of a 6-ns 750-mJ Nd:YAG laser at the fundamental wavelength of 1.06 µm with a standard Al target of known elemental composition in air. The emitted spectrum was in the range 200–1000 nm and was recorded using an Echelle spectrograph equipped with a time-gated ICCD camera. The measurements were performed at several delay times (0–10 µs). Based on LTE assumption, the excitation temperature is derived using a Boltzmann plot of OI emission lines. The FWHM of the Stark broadened OI line at 844.65 nm is used for electron density measurements at different times.