共查询到20条相似文献,搜索用时 31 毫秒
1.
《Physics letters. A》2002,302(4):182-189
The gas dynamics of pulsed laser ablation of silicon target in the helium gas ambient is investigated via direct simulation Monte Carlo method with a real physical scale of target-substrate configuration. A shock driven process is clearly observed. It is shown that the interaction of the shock front with the target surface and the vapor front induce significant backward flux of ablated particles and oscillating behavior of vapor front. A confined layer mixed with high density Si and He atoms is formed around the contact front. Its behavior is important to the nanoparticle formation and deposition. 相似文献
2.
Femtosecond(fs) pulse laser ablation of silicon targets in air and in vacuum is investigated using a timeresolved shadowgraphic method. The observed dynamic process of the fs laser ablation of silicon in air is significantly different from that in vacuum. Similar to the ablation of metallic targets,while the shock wave front and a series of nearly concentric and semicircular stripes,as well as the contact front,are clearly identifiable in the process of ablation under 1×10 5 Pa,these phenomena are no longer observed when the ablation takes place in vacuum. Although the ambient air around the target strongly affects the evolution of the ablation plume,the three rounds of material ejection clearly observed in the shadowgraphs of fs laser ablation in standard air can also be distinguished in the process of ablation in vacuum. It is proven that the three rounds of material ejection are caused by different ablation mechanisms. 相似文献
3.
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。 相似文献
4.
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。 相似文献
6.
A. Bailini 《Applied Surface Science》2006,252(13):4364-4367
The effect of inert gas ionization on the dynamics of a laser ablation plume expanding through a background inert gas is studied. Charge transfer reactions between ablated ions and neutral background gas atoms yield to the formation of a charged layer on the plume expansion front. The energy lost by ablated ions when the plume is slowed down is calculated. The observed microstructure differences between carbon films prepared by pulsed laser deposition in helium, where the ionization mechanism is absent and respectively in argon, where it is present, are well correlated to model predictions. 相似文献
7.
Experimental results concerning the interaction of pulsed volume ionization with the supersonic gas flow in a shock tube are described. The spatiotemporal and spectral characteristics of a nanosecond volume discharge plasma with ultraviolet preionization from plasma electrodes are presented. It is shown that the ionization region can be localized using gasdynamic discontinuities. The coincidence of the glow region with the discharge energy release region is discussed. 相似文献
8.
A new finite-difference method for the numerical solution of gas dynamics equations is proposed. This method is a uniform
monotonous finite-difference scheme of second-order approximation on time and space outside of domains of shock and compression
waves. This method is based on inputting adaptive artificial viscosity (AAV) into gas dynamics equations. In this paper, this
method is analyzed for 2D geometry. The testing computations of the movement of contact discontinuities and shock waves and
the breakup of discontinuities are demonstrated. 相似文献
9.
Time-resolved shadowgraphs and morphology analyses of aluminum ablation with multiple femtosecond laser pulses 下载免费PDF全文
Aluminum ablation by multiple femtosecond laser pulses is investigated via time-resolved shadowgraphs and scanning electron microscope(SEM) images of the ablation spot. The spatial distribution of the ejected material and the radius of the shock wave generated during the ablation are found to vary with the increase in the number of pulses. In the initial two pulses, nearly concentric and semicircular stripes within the shock wave front are observed, unlike in subsequent pulses. Ablation by multiple femtosecond pulses exhibits different characteristics compared with the case induced by single femtosecond pulse because of the changes to the aluminum target surface induced by the preceding pulses. 相似文献
10.
I. A. Doroshchenko I. A. Znamenskaya A. Yu. Kuznetsov I. V. Mursenkova N. N. Sysoev 《Technical Physics》2018,63(5):662-669
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. 相似文献
11.
The influence of inert gas ionisation on the expansion dynamics of a laser ablation plume propagating through an inert gas is studied. Charge transfer reactions between ionised ablated species and gas neutrals lead to the formation of a charged layer of ionised gas atoms in contact with the plume expansion front. The energy lost by fast ablated ions when the plume is slowed down is calculated. For the exemplary carbon ablation in helium and argon atmospheres, where background gas ionisation plays a different role, model predictions agree with the observed microstructural differences of deposited films. 相似文献
12.
Shadowgraph investigation of plasma shock wave evolution from Al target under 355-nm laser ablation 下载免费PDF全文
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. 相似文献
13.
U.?Yusupaliev 《Bulletin of the Lebedev Physics Institute》2009,36(8):239-244
Using an ionization sensor, it was found that weakly ionized plasma with an ionization degree larger than 10?6 is formed under exposure to UV radiation of a high-current pulsed electric discharge in gas (air, nitrogen, xenon, and krypton) at atmospheric pressure at a distance of ~1.2–2.5 cm from the discharge boundary. It was shown that the structure of such discharge includes, in addition to the discharge channel, a dense shell and a shock wave, also a region of weakly ionized and excited gas before the shock wave front. The mechanism of discharge expansion in dense gas is ionization and heating of gas involved in the discharge due to absorption of the UV energy flux from the discharge channel and the flux of the thermal energy transferred from the discharge channel to the discharge shell due to electron thermal conductivity. 相似文献
14.
U. Yusupaliev 《Bulletin of the Lebedev Physics Institute》2009,36(8):245-251
Using an ionization sensor, it was found that weakly ionized plasma with an ionization degree larger than 10−6 is formed under exposure to UV radiation of a high-current pulsed electric discharge in gas (air, nitrogen, xenon, and krypton)
at atmospheric pressure at a distance of ∼1.2–2.5 cm from the discharge boundary. It was shown that the structure of such
discharge includes, in addition to the discharge channel, a dense shell and a shock wave, also a region of weakly ionized
and excited gas before the shock wave front. The mechanism of discharge expansion in dense gas is ionization and heating of
gas involved in the discharge due to absorption of the UV energy flux from the discharge channel and the flux of the thermal
energy transferred from the discharge channel to the discharge shell due to electron thermal conductivity. 相似文献
15.
The effect of creation of an excess concentration of free electrons in an anomalously thick layer (≈5 cm) ahead of an explosively
driven shock wave in noble gases is discussed and interpreted. This effect is the ionization of excited 1u-state molecules produced due to the absorption of a small intensity flux (as compared to the ionization one) of photons (with
energies substantially lower than the atom ionization threshold) by unexcited colliding complexes and van der Waals molecules.
A model is proposed which explains the excitation of xenon molecules ahead of the radiationless shock wave of an open discharge.
The absorption spectra of colliding complexes and van der Waals molecules adjacent to each other near the atomic absorption
lines can be resolved into two spectra, and these spectra can be changed by an increase in gas temperature. As a result, radiation
capable of exciting van der Waals molecules penetrates through the shock wave of an open discharge and excites xenon molecules
there.
The present work develops further the knowledge concerning the radiation energy transport in the shock wave front. It also
proves that in front of an explosively driven shock wave a great number of excited molecules of noble gases are actually formed,
and this means considerable progress toward a VUV laser with optical pumping.
Translated from Preprint No. 56 of the P. N. Lebedev Physical Institute, Moscow, 1993. 相似文献
16.
Aivaras Urnie?ius Nerijus ?iaulys Via?eslav Kudria?ov Valdas Sirutkaitis Andrius Melninkaitis 《Applied Physics A: Materials Science & Processing》2012,108(2):343-349
We studied evolution of femtosecond laser ablation by employing novel method of time-resolved off-axis digital holographic microscopy. Phase and amplitude profiles of early shock front and ablation plume dynamics of irradiated tempered steel were reconstructed from the digital holograms. In order to gain additional information, digital holographic microscopy was combined with plasma emission imaging. By using both techniques simultaneously we studied material response to multi-pulse irradiation, shock wave propagation, ablation plume formation and plasma emission. The significant changes in ablation performance were observed when using multi-pulse irradiation if compared to widely investigated single-shot regime. 相似文献
17.
18.
激光在半导体加工行业(特别是硅材料)具有广阔的应用前景。激光与硅作用过程极其复杂,本文主要研究了紫外激光脉冲对硅进行烧蚀的形貌特征以及环境气体的影响。研究表明,紫外激光烧蚀硅产生激光等离子体的电离效应对烧蚀特性起了决定性的影响:气化、电离物的产生为材料的去除提供了条件,同时激光等离子体冲击波会把相变材料有效排出,激光等离子体光谱的电离效应则把空气中的氧元素有效电离并沉积到烧蚀产物中。 相似文献
19.
Experimental observation of ionization and shock fronts in foam targets driven by thermal radiation 下载免费PDF全文
The behaviours of ionization and shock propagation in
radiatively heated material is crucial for the understanding of
indirect drive inertial confinement fusion as well as some
astrophysics phenomena. In this work, radiation field with a peak
temperature of up to 155 eV was generated in a gold cavity heated by
four laser beams on the SG-II laser system and was used to irradiate
a plastic foam cylinder at one end. The radiatively ablated foam
cylinder was then backlighted side-on by x-ray from a
laser-irradiated Ti disk. By observing the transmission decrease due
to the shock compression of the foam cylinder, the trajectories of shock
front were measured, and from the onset of the intense thermal
emission from the side of the cylinder, the propagations of
the ionization front were also observed on the same shot. The
experimental measurements were compared to predictions of the
radiation hydrodynamics code Multi-1D and reasonable agreements were
found. 相似文献