Experimental investigation of plume expansion dynamics of nanosecond laser ablated Al with small incident angle

Experimental study of expansion dynamics of pulsed-laser ablation plasmas from Al is presented. A systematic investigation of plasma plume expansion is done. The laser beam is focused on the target with an incident angle between 0° and 20°. The results show that the plume growth is almost normal to the target surface, irrespective of the incident angle of the laser. Besides, the time evolution of the plasma plume geometry ratio at different incident angles shows that the incident angle of laser beam influences very slightly its shape at later delay time. The results imply that when the incident angle is small (ranging from 0° to 20°), the influence of the incident angle on the plume expansion is rather trivial.     

Spatial and time resolved analysis of CN bands in the laser induced plasma from graphite

Analysis of the emission bands of the CN molecules in the plasma generated from a graphite target irradiated with 1.06 μm radiation pulses from a Q-switched Nd:YAG laser has been done. Depending on the position of the sampled volume of the plasma plume, the intensity distribution in the emission spectra is found to change drastically. The vibrational temperature and population distribution in the different vibrational levels have been studied as function of distance from the target for different time delays with respect to the incidence of the laser pulse. The translational temperature calculated from time of flight is found to be higher than the observed vibrational temperature for CN molecules and the reason for this is explained.     

New fast spectral analysis method for solid materials

We propose a new fast method for direct spectral analysis of solid materials based on laser ablation of the sample in deionized water and real-time transport of the aqueous suspension of nanoparticles into the inductively coupled plasma of an emission spectrometer. As a result, we have all the instrumental and methodological advantages of standard equipment, along with calibration of the spectrometer using standard aqueous solutions. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 3, pp. 281–282, May–June, 2007.     

飞秒激光烧蚀硅表面产生等离子体的发射光谱研究

对中心波长为800 nm,脉宽为100 fs的激光脉冲烧蚀空气中硅(111)产生的等离子体发射光谱进行了时间和空间分辨研究. 结果表明,在等离子体羽膨胀初期(小于50 ns时间范围内),等离子体发射光谱主要由连续光谱构成,此后连续光谱强度逐渐减弱,线状光谱开始占主导地位;在羽体膨胀过程中离子谱线的存在时间短于原子谱线的存在时间. 由时间分辨发射光谱发现在羽体膨胀过程中等离子体辐射波长存在红移现象,波长红移量随时间演化呈二次指数衰减. 最后给出等离子体发射光谱谱线强度的时空演化规律. 关键词： 飞秒激光 脉冲激光烧蚀 等离子体 发射光谱     

Spectroscopic studies of sodium nitrate plasma produced by nanosecond laser ablation

We present the optical emission characteristics of the sodium plasma produced at the surface of sodium nitrate (NaNO₃) also known as Chile saltpeter. We used a Q-switched Nd:YAG (Quantel Brilliant) pulsed laser having a pulse duration of 5?ns and 10?Hz repetition rate which is capable of delivering 400?mJ at 1064?nm and 200?mJ at 532?nm. The target material was placed in front of laser beam in air (atmospheric pressure). The experimentally observed line profiles of neutral sodium have been used to extract the electron temperature using the Boltzmann plot method, whereas the electron number density has been determined from the Stark broadening. The electron temperature is calculated by varying the distance from the target surface along the line of propagation of the plasma plume and also by varying the laser irradiance. Besides, we have studied the variation of number density as a function of laser irradiance as well as its variation with the distance from the target surface. It is observed that electron temperature and electron number density increase as the laser irradiance is increased.     

脉冲激光烧蚀Ge产生等离子体特性的数值模拟

针对激光烧蚀半导体材料Ge初期的特点,建立了1维的热传导和流体动力学模型。对波长为248 nm、脉宽为17 ns、峰值功率密度为4×108 W/cm2的KrF脉冲激光在133.32 Pa氦气环境下烧蚀Ge产生等离子体的特性进行了数值模拟。结果表明：单个激光脉冲对靶的烧蚀深度达到55 nm,蒸气膨胀前端由于压缩背景气体产生压缩冲击波, 波前的速度最大,温度很高。从不同时刻的电离率分布图中得出,在靶面附近区域,Ge的1阶电离始终占优势;在中心区域,脉冲作用时间内,Ge的2阶电离率比1阶电离率大,脉冲结束后,Ge的2阶电离率下降,1阶电离率逐渐变大。     

脉冲Nd∶YAG激光烧蚀Al产生等离子体特征辐射的机理研究

采用时间与空间分辨光谱测量技术,研究了在Ar气为缓冲气体下,用脉冲Nd∶YAG激光烧蚀Al产生等离子体的发射光谱及其随气压的变化规律,对粒子的激发机理进行了讨论,认为特征谱线是由复合辐射为主要机理,并用此结论在一定程度上解释了实验结果。     

Emission properties of laser ablation of SnO2: Sb transparent conducting film and KTiOPO4 crystal

Optical emission spectra of Nd:YAG laser ablation of KTiOPO₄ (KTP) crystal and SnO₂:Sb transparent conducting thin film were recorded and analyzed in vacuum and in air. The integral intensities of spectral lines from laser-ablated KTP crystal were obtained as functions of distance from the target surface and laser power density in vacuum and in air. The ambient gas effects on pulsed laser ablation of target were discussed. We also performed laser ablation of SnO₂:Sb transparent conducting thin film in air and the electron temperature and full-width at half-maximum (FWHM) of atomic and ionic spectral lines in the plasma were quantified using Boltzmann plot method and Lorentzian fit, respectively. Integral intensities of atomic and ionic Sn spectral lines were also obtained as functions of distance from the target surface and laser irradiance. The intensity ratio of ionic and atomic Sn spectral lines as a function of laser power density was got which gives some information about the variation of ionization ratio with laser irradiance in the plasma produced by high-power laser.     

激光脉冲能量对激光诱导Al等离子体辐射特征的影响

使用Nd：YAG激光器烧蚀金属Al靶获得等离子体,利用光谱时-空分辨技 术,在52 mJ～145 mL/pulse激光脉冲能量范围内,关于激光脉冲能量对激光诱导等离子体 辐射特征的影响进行了研究。使用的气体是Ar气,压强为10 kPa。结果发现,激光脉冲能量 升高,引起特征谱线强度增加,连续谱强度也增加;但能量过高,会击穿周围气体,产生气 体微等离子体。此时,特征谱和连续谱几乎不再增强;最大特征辐射强度在145 mJ、10 kPa 、靶前0.1 mm处、延时180 ns获得;同一条件下获得最强背景连续谱,而信号-背景差是在 145 mJ、10 kPa、靶前1.0 mm处、延时450 ns达到最大值。基于Al等离子体不同激光脉冲能 量下的时间-空间分辨谱,对结果进行了简单的讨论。并分别确定了获得最大特征辐射和信 号-背景差的条件。     

Laser plasma plume kinetic spectroscopy of the nitrogen and carbon species

The formation and decay of carbon and nitrogen atoms, CN radicals and C₂ molecules were monitored using spatial‐ and time‐resolved emission spectroscopy in a plasma plume formed during laser ablation of a graphite target in nitrogen atmosphere. A simple exponential model was used to explain the effect of the individual chemical reactions and plasma dynamics on the measured kinetic characteristics. The succession of emissions C → N → CN was observed in the time‐resolved spectra, supporting the suggestion that the CN radical is formed mainly by the direct reaction C + N → CN or C₂ + N₂ → 2CN. The formation of CN radical was enhanced by the additional generation of atomic nitrogen through the RF discharge. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Surface ablation of lithium tantalate by femtosecond laser

We report measurements of the laser induced breakdown threshold in lithium tantalate with different number of pulses delivered from a chirped pulse amplification Ti: sapphire system. The threshold fluences were determined from the relation between the diameter D² of the ablated area and the laser fluence F₀. The threshold of lithium tantalite under single-shot is found to be 1.84 J/cm², and the avalanche rate was determined to be 1.01 cm²/J by calculation. We found that avalanche dominates the ablation process, while photoionization serves as a free electron provider.     

激光能量对激光诱导Cu等离子体特征辐射强度、电子温度的影响

利用Nd:YAG激光(波长1 064 nm,脉宽10 ns)烧蚀金属Cu靶获得等离子体 .改变激光脉冲能量,观测到Cu的原子谱线和离子谱线随激光脉冲能量有不同的变化关系, 但都在330 mJ/pulse时,谱线强度达到最大,随后在330 mJ～370 mJ/pulse间出现一小平台 ,能量继续增加,各谱线强度减小.同时,使用烧蚀Cu靶产生的五条原子谱线(465.11 nm,5 10.55 nm,515.32 nm,521.82 nm,529.25 nm)的相对强度,在局部热力学平衡近似下,利用B oltzmann图的最小二乘法拟合,测定了不同激光能量下Cu等离子体的电子温度.随激光能量的增加,电子温度近似单调地从1.02×104 K上升到1.46×104 K后,反而有所下降.     

辉光等离子体辅助化学气相沉积低温合成金刚石薄膜的研究

采用辉光放电等离子体增强化学气相沉积 (GP CVD)技术在低温条件下合成了高品质的亚微米金刚石薄膜 ,并通过对合成过程的实时发射光谱诊断确定了 [CH4 H2 ]系统参与金刚石合成反应的主要荷能粒子。对合成过程的研究表明 :采用这种技术能使电子增强热丝化学气相沉积 (EACVD)合成高品质金刚石薄膜的温度从 85 0℃降至 (340± 5 )℃ ;薄膜低温合成中的主要荷能粒子为CH3 、CH ,CH+ 、H 等 ,其中过饱和原子氢保证了高品质金刚石薄膜的合成 ;根据光诊断和探针测量的结果推断近表面辉光放电可在基片表面形成电偶极层 ,该偶极层是进行超常态反应的必要环境 ,并在低温合成中起重要作用     

Investigation of plumes produced by material ablation with two time-delayed femtosecond laser pulses

We experimentally investigated and herewith reported the results of laser ablation of copper and gold with two time-delayed femtosecond laser pulses at 800 nm in vacuum. The ablation plume dynamic was monitored by fast plume imaging and time- and space-resolved optical emission spectroscopy. Optical microscopy was used to follow the ablation depth as a function of the delay between the two laser pulses. Nanoparticles deposition on mica substrates was analysed by atomic force microscopy.We estimate roughly the plume's atomization degree - that is the mass fraction of atomized material over the total ablated mass - from the relative intensities of radiation emitted from atoms and nanoparticles. It is shown that the atomization degree depends critically on the time delay between both laser pulses and on the characteristic time of electron-lattice relaxation. The increase of the atomization degree is accompanied by the decrease of the ablation depth. Atomic force microscopy measurements confirm the partial atomization of nanoparticles, as the analyses of particle deposition on mica substrates show a large decrease of the number of nanoparticles for large delay between the two pulses.     

Laser ablation of AsxSe100−x chalcogenide glasses: Plume investigations

The use of amorphous chalcogenides offers advantages such as remarkable optical properties like a wide transmission window (∼1-20 μm) depending upon composition, making them suitable for sensitive detection of clinical or environmental changes. They also present interesting high (non)linear refractive indices, photorefractive effects, and other properties interesting for wavelength conversion, all-optical switching or modulation, Raman and parametric amplification, laser sources for mid-IR, etc.Slab waveguides based on chalcogenide amorphous films with good adherence and controlled composition can be obtained using pulsed laser deposition allowing to design and to manufacture complex optical functions on waveguides within a small and compact chip. The aim of this work is to characterize the ejection plume obtained by laser ablation of As_xSe_100−x samples in order to get some insight on the process involved for optimizing the pulsed laser deposition process. The dynamics of the plume has been systematically investigated by ICCD camera fast imaging and space- and time-resolved optical emission spectroscopy for samples of various compositions.     

Study of the X-ray emission from Ta plasma obtained by ns laser ablation

In this work, the continuum spectrum of X-rays originated from the interaction of a moderate intensity ns Nd:YAG laser (1064 nm, 9 ns, 30 Hz, 900 mJ, 10¹¹ W/cm²) with Ta target producing plasma is investigated. Plasma expands unisotropically with a velocity, depending on the pressure of the residual gas in the vacuum chamber. The X-ray intensity is a function of the laser energy and of the gas pressure inside the chamber. The X-ray energy is measured with an X-ray filter positioned in front of the Si(Li) solid-state detector. A temperature of about ～1–2 keV of the hot electrons, responsible for the continuum spectrum emission from the plasma, is calculated from the fit of the X-ray spectrum, applying a Maxwellian distribution.     

光谱诊断冷等离子体作用下甲烷转化机理的初步研究(英文)

冷等离子体是甲烷无氧活化制C2烃较为有效的技术手段之一,由于等离子体反应体系的复杂性,甲烷无氧活化制C2烃反应机理及过程尚不十分清楚。本文采用发射光谱原位诊断技术对冷等离子体作用下甲烷无氧活化制C2烃反应中若干激发态物种进行诊断研究,在250nm～670nm波长范围内检测到下列激发态物种:CH、C和C2。依据激发态物种检测结果、气相色谱反应产物分析结果及等离子体特性,推断了等离子体作用下甲烷无氧活化制C2烃的自由基反应历程。     

脉冲光纤激光修锐青铜金刚石砂轮等离子体特性研究

采用光栅光谱仪 对脉冲光纤激光修锐青铜金刚石砂轮过程中产生的等离子体空间分辨发射光谱进行了测量. 研究了500–600 nm波段范围内的等离子体空间发射光谱强度随激光平均功率和脉冲重复频率的变化情况. 结果表明: 等离子体辐射光谱强度在其径向膨胀方向上距离砂轮表面约2.4 mm处达到最大值. 在局部热力学平衡假设条件下, 根据等离子体中六条铜原子谱线的相对强度, 利用Boltzmann 图法, 计算得到在不同激光功率和重复频 率条件下的等离子体电子温度沿砂轮径向方向的分布规律. 实验结果表明: 在激光修锐青铜金刚石砂轮过程中, 距离砂轮表面约3 mm处等离子体电子温度出现峰值, 其温度最高可达4380 K, 且等离子体电子温度随着激光参数和 空间位置的改变呈现出不同的演变规律. 关键词： 脉冲光纤激光 等离子体发射光谱 激光修锐 电子温度     

射频感应耦合低压等离子体特性分析

采用光谱诊断法和Langmuir单探针法对射频感应耦合Ar气等离子体特性进行分析。通过光栅光谱仪研究了低气压下Ar气等离子体的光谱强度的变化特性,采用Langmuir单探针法测量不同条件下电子密度和电子温度。等离子体发射光谱的光谱强度随着气压和功率的增加而增强,射频功率对光谱强度的影响较明显。当功率从120W增加到180W时,光谱强度将会迅速增加,等离子体发生E模向H模的模式转换。Langmuir单探针法测量的电子密度和电子温度在的变化规律符合E模向H模转换的变化规律。     

气压对激光诱导Al等离子体特征的影响

使用Nd :YAG激光器烧蚀金属Al靶获得等离子体 ,利用光谱时 -空分辨技术 ,在 10 0～ 1× 10 5Pa气压范围内 ,关于环境气体压强对激光诱导的等离子体辐射特征的影响进行了研究。使用的气体是Ar气 ,单脉冲激光能量 145mJ。结果发现 ,气压升高 ,特征谱线强度增加 ,连续谱强度也增加 ;但气压过高 ,在接近大气压时 ,特征谱和连续谱都下降 ;最大特征辐射强度在 10kPa、靶前 0 .1mm处、延时 180ns获得 ;同一条件下获得最强背景连续谱 ,而信号 -背景比是在10 0 0Pa、靶前 1.0mm处、延时 2 50 0ns达到最大值。基于Al等离子体不同气压下的时间 -空间分辨谱 ,对结果进行了简单的讨论。并分别确定了获得最大特征辐射和信号 -背景比的条件 ;以及最佳信号采集区。