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1.
Thermoelastic wave induced by pulsed laser heating 总被引:6,自引:0,他引:6
In this work, a generalized solution for the thermoelastic plane wave in a semi-infinite solid induced by pulsed laser heating
is developed. The solution takes into account the non-Fourier effect in heat conduction and the coupling effect between temperature
and strain rate, which play significant roles in ultrashort pulsed laser heating. Based on this solution, calculations are
conducted to study stress waves induced by nano-, pico-, and femtosecond laser pulses. It is found that with the same maximum
surface temperature increase, a shorter pulsed laser induces a much stronger stress wave. The non-Fourier effect causes a
higher surface temperature increase, but a weaker stress wave. Also, for the first time, it is found that a second stress
wave is formed and propagates with the same speed as the thermal wave. The surface displacement accompanying thermal expansion
shows a substantial time delay to the femtosecond laser pulse. On the contrary, surface displacement and heating occur simultaneously
in nano- and picosecond laser heating. In femtosecond laser heating, results show that the coupling effect strongly attenuates
the stress wave and extends the duration of the stress wave. This may explain the minimal damage in ultrashort laser materials
processing.
Received: 23 May 2000 / Accepted: 26 May 2000 / Published online: 20 September 2000 相似文献
2.
R. Lopez R. Ruiz R.F. Haglund Jr. L.C. Feldman 《Applied Physics A: Materials Science & Processing》2002,74(2):307-310
We describe the fabrication by room-temperature pulsed laser deposition of a transparent conductor comprising alternating
layers of silver and aluminum oxide, forming a metallo-dielectric filter. Transmittances of 0.7 over specific wavelength bands
were achieved with resistivities as low as 6.0×10-6 Ω cm, almost two orders of magnitude lower than that of the best single-substrate thin films, such as indium tin oxide. The
resistivity can be predicted without adjustable parameters and designed using a simple parallel-circuit model; the optical
properties are well described by standard matrix transmission calculations. This demonstrates that pulsed laser deposition
may be used to fabricate prototypes of high-quality transparent conductors with predictable properties for conducting windows
where low-temperature deposition is critical, as in organic light-emitting diodes and for non-linear optical films.
Received: 10 June 2001 / Accepted: 9 August 2001 / Published online: 20 December 2001 相似文献
3.
In this paper we report the results of an investigation into surface deformation caused by thermal effects during excimer
laser ablation of polyimide. Obvious surface deformation around hole entrances was observed during the experiment. The surface
topology and cross section of the ablated holes were analyzed using topography measurement tool and scanning electron microscopy.
It was shown that a micro-hump of 17 to 150 nm in height and 1 to 3 μm in width was formed above the level of the unablated
surface. The deformed surface showed rough and color-changed characteristics. An optical diffraction model was employed to
explain the cause of this kind of deformation. It was found that the ablating and heating by a near- and under-threshold laser
beam became a thermal effect in polyimide material ablation, which was contributed to by a diffraction effect of the optical
projection system.
Received: 9 October 2001 / Accepted: 17 October 2001 / Published online: 23 January 2002 相似文献
4.
C. Grivas S. Mailis R.W. Eason E. Tzamali N.A. Vainos 《Applied Physics A: Materials Science & Processing》2002,74(4):457-465
UV (325 nm) holographic recording of gratings in indium oxide films fabricated by reactive pulsed laser deposition has been
investigated as a function of growth temperature, oxygen pressure and angle of incidence of the plasma plume on the substrate.
The influence of the ambient environment (air or vacuum) and the film temperature during recording has also been studied.
Large steady state refractive index changes up to 6×10-3 were observed in layers grown at an oblique angle of 75°. About 77% of the magnitude of these changes residues after thermal
annealing and is attributed to UV-induced permanent structural rearrangements. In contrast, refractive index changes in films
grown at normal incidence were smaller in magnitude and completely reversible.
Received: 30 July 2001 / Accepted: 20 November 2001 / Published online: 23 January 2002 相似文献
5.
A compact self-seeded pulsed tunable laser is described. Its optical cavity comprises a diffraction grating, operating at
a grazing angle of incidence as a spectral selector and narrow-band spectral gate. The grating couples two partially overlapping
laser channels: a highly selective master laser and a nonselective slave laser. Due to the implemented efficient intracavity
self-seeding the laser emits spectrally pure single-longitudinal-mode radiation at two independently tunable wavelengths,
with an efficiency and output energy that are typical for nonselective lasers. Results of the experimental investigation of
the laser’s output characteristics are presented.
Received: 12 March 2001 / Revised version: 10 December 2001 / Published online: 7 February 2002 相似文献
6.
The present work develops two numerical models to compute thermal phenomena during pulsed laser welding. The first one which is based on finite difference model calculates the welding width and its penetration by utilizing heat transfer equations. Parametric design capabilities of the finite element code ANSYS were also employed for the simulation of the second model. The transient temperature profiles, the fusion dimensions and the heat affected zones (HAZ) have been calculated here. The thermo-physical properties are dependent on temperature and so a nonlinear solution is employed. It is found that the temperature profile and penetration depth are strongly dependent on the pulse parameters of laser beam. Finally, the results of the two models and the experimental outcomes are compared. 相似文献
7.
WANG Xiaodong PENG Xiaofeng & ZHANG Duanming Laboratory of Phase Change Interfacial Transport Phenomena Department of Thermal Engineering Tsinghua University Beijing China Department of Physics Huazhong University of Science Technology Wuhan China 《中国科学G辑(英文版)》2005,48(1):33-43
Using the Sol-Gel method to produce the KTN ultrafine powder and the sintering technique with K2O atmosphere to prepare KTN ceramics as the targets instead of the KTN single crystal, highly oriented KTN thin films were produced on the transparent single crystal quartz (100) by the pulsed laser deposition (PLD). Since the thermal stress sustained by the quartz is relatively small, the limit temperature of the quartz substrates (300℃) is much lower than that of the P-Si substrates (560℃); the prepared thin film is at amorphous state. Increasing the pulsed laser energy density in the process incorporated with annealing the film after deposition at different temperatures converts the amorphous films into crystal. The optimal pulsed laser energy density and annealing temperature were 2.0 J/cm2 and 600℃, respectively. A discussion was made to understand the mechanism of film production at relatively low substrate temperature by PLD and effects of the annealing temperatures on the forming of the perovskite p 相似文献
8.
G. Perna V. Capozzi 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(4):401-406
CdSe and CdS films, deposited on a sapphire substrate by means of pulsed laser ablation technique, have been investigated
by means of reflectivity and photoluminescence measurements in order to study the effect of such a transparent substrate on
the optical properties of the deposited epilayers. The reflectivity spectra at low temperature have been studied by means
of an analytical model which permits one to obtain the energies of the excitonic resonances. The photoluminescence spectra
show that our CdSe and CdS films present excitonic emission at low temperature, differently from the same films deposited
on quartz. The temperature dependence of the excitonic energy has been analysed by taking into account the contribution of
both the thermal expansion and electron-phonon interaction. The exciton linewidth has been analysed according to well known
phenomenological models.
Received 21 June 2001 and Received in final form 18 November 2001 相似文献
9.
Jijun Wang Zhonghua Shen Baiqiang Xu Xiaowu Ni Jianfei Guan Jian Lu 《Optics & Laser Technology》2007,39(4):806-813
The use of a pulsed laser for the generation of the elastic waves in non-metallic materials in the thermoelastic regime is investigated by using finite element method (FEM), taking into account not only thermal diffusion and the finite spatial and temporal shape of the laser pulse, but also optical penetration and the temperature dependence of material properties. The optimum finite element model is established based on analysis of two important parameters, meshing size and time step, and the stability of solution. Temperature distributions and temperature gradient fields in non-metallic material for different time steps are obtained, this temperature field is equivalent to a bulk force source to generate ultrasonic wave. The laser-generated ultrasound waveforms at the epicenter and surface acoustic waveforms (SAWs) are obtained and the influence of optical penetration into the material on the temperature field and the ultrasound waveforms are analyzed. The numerical results indicate that the heat penetration into non-metallic material is caused mainly by the optical penetration, and the ultrasound waveforms, especially the shape of the precursor, are strongly dependent on the optical penetration depth into non-metallic material. 相似文献
10.
S. Ito H. Nagaoka T. Miura K. Kobayashi A. Endo K. Torizuka 《Applied physics. B, Lasers and optics》2002,74(4-5):343-347
We have measured detailed thermal lensing in a power amplifier of a terawatt Ti:sapphire laser operating at 50 Hz. The thermal
lensing in the amplifier was evaluated by measuring the optical path difference (OPD) using a Shack–Hartmann-type wavefront
sensor. It was found that the radial dependence of the OPD was almost quadratic in the pumping region, despite inhomogeneous
pumping. Therefore, a simple spherical lens or convex mirror effectively compensates for the thermal lens in our amplifier.
We found that the thermal lens profile was temporally stable, and did not degrade the pointing stability of the amplified
laser pulses. We also found that the time constant of the thermal distortion in our power amplifier was approximately 0.5 s.
Received: 3 September 2001 / Revised version: 23 January 2002 / Published online: 14 March 2002 相似文献
11.
Characteristics of thermo-mechanical laser ablation process are investigated using an original numerical model. In contrast
with previous models, it is based on a microscopic physical model of the micro-explosion process, which combines thermodynamic
behavior of tissue water with elastic response of the solid tissue components. Diffusion of dissipated heat is treated in
one dimension, and the amount of thermal damage is assessed using the Arrhenius model of the protein denaturation kinetics.
Influence of the pulse fluence and duration on temperature profile development, ablation threshold, and depth of thermal damage
is analyzed for the case of Er:YAG laser irradiation of human skin. Influence of mechanical properties on the ablation threshold
of soft tissue is predicted theoretically for the first time. In addition, feasibility of deep tissue coagulation with a repetitively
pulsed Er:YAG laser is indicated from the model.
Received: 9 July 1998 / Revised version: 26 February 1999 / Published online: 26 May 1999 相似文献
12.
D.M. Bubb B. Toftmann R.F. Haglund Jr. J.S. Horwitz M.R. Papantonakis R.A. McGill P.W. Wu D.B. Chrisey 《Applied Physics A: Materials Science & Processing》2002,74(1):123-125
Thin films of the biodegradable polymer poly(DL-lactide-co-glycolide) (PLGA) were deposited using resonant infrared pulsed
laser deposition (RIR-PLD). The output of a free-electron laser was focused onto a solid target of the polymer, and the films
were deposited using 2.90 (resonant with O-H stretch) and 3.40 (C-H) μm light at macropulse fluences of 7.8 and 6.7 J/cm2, respectively. Under these conditions, a 0.5-μm thick film can be grown in less than 5 min. Film structure was determined
from infrared absorbance measurements and gel permeation chromatography (GPC). While the infrared absorbance spectrum of the
films is nearly identical with that of the native polymer, the average molecular weight of the films is a little less than
half that of the starting material. Potential strategies for defeating this mass change are discussed.
Received: 22 August 2001 / Accepted: 23 August 2001 / Published online: 17 October 2001 相似文献
13.
F. Kokai M. Taniwaki M. Ishihara Y. Koga 《Applied Physics A: Materials Science & Processing》2002,74(4):533-536
We deposited amorphous thin films of boron carbide by pulsed laser deposition using a B4C target at room temperature. As the laser fluence increased from 1 to 3 J/cm2, the number of 0.25–5 μm particulates embedded in the films decreased, and the B/C atomic ratio of the films increased from
1.8 to 3.2. The arrival of melt droplets, atoms, and small molecular species depending on laser fluence appeared to be involved
in the film formation. In addition, with increasing fluence the nanoindentation hardness of the films increased from 14 to
32 GPa. We believe that the dominant factor in the observed increase in the films’ hardness is the arrival of highly energetic
ions and atoms that results in the formation of denser films.
Received: 23 March 2001 / Accepted: 1 July 2001 / Published online: 2 October 2001 相似文献
14.
15.
T. Li Q. Lou J. Dong Y. Wei J. Liu 《Applied Physics A: Materials Science & Processing》2000,71(3):271-276
Numerical calculations based on a thermal model were presented, which describe the process of target heating and ablation
of cobalt during irradiation by 30-ns laser pulses at 308 nm. The attenuation of laser by vapor has been taken into account
in this model. As results of the calculations, the temperature distribution beneath the target surface and the temporal evolution
of surface temperature were given. The dependence of ablation rate on laser fluence was also studied based on this model.
The surface ablation of cobalt with pulsed excimer laser was investigated experimentally. Our model considering proper vapor
attenuation has shown to be in good agreement with the experimental results.
Received: 20 January 2000 / Accepted: 13 March 2000 / Published online: 5 July 2000 相似文献
16.
Vaporization and Plasma Shielding during High Power Nanosecond Laser Ablation of Silicon and Nickel 下载免费PDF全文
A thermal model to describe the high-power nanosecond pulsed laser ablation is presented. It involves the vaporization and the following plasma shielding effect on the whole ablation process. As an example of Si target, we obtainthe time evolution of the calculated surface temperature, ablation rate and ablation depth. It can be seen that plasma shielding plays a more important role in the ablation process with time. At the same time, the ablation depth with laser fluence based on different models is shown. Moreover, we simulate the pulsed laser irradiation Ni target. The evolution of the transmitted intensity and the variation of ablation depth per pulse with laser fluence are performed. Under the same experimental conditions, the numerical results calculated with our thermal model are more in agreement with the experimental data. 相似文献
17.
Ion synthesis and laser annealing of Cu nanoparticles in Al2O3 总被引:1,自引:0,他引:1
A.L. Stepanov V.N. Popok D.E. Hole I.B. Khaibullin 《Applied Physics A: Materials Science & Processing》2002,74(3):441-446
Al2O3 samples with Cu nanoparticles, synthesised by ion implantation at 40 keV with a dose of 1×1017 ion/cm2 and a current density from 2.5 to 12.5 μA/cm2, were annealed using ten pulses from a KrF excimer laser with a single pulse fluence of 0.3 J/cm2. The copper depth distribution, formation and modification of metal nanoparticles under the ion implantation and laser treatment
were studied by Rutherford backscattering (RBS), energy dispersive X-ray (EDX) analysis, atomic force microscopy (AFM) and
optical spectroscopy. It was found that laser annealing leads to a reduction in the nanoparticle size without diffusion of
metal atoms into the bulk. The change in particle size and the possibility for oxidation of the copper particles are examined
in the framework of Mie theory. Calculations presented show that under excimer laser treatment, Cu nanoparticles are more
likely to be reduced in size than to undergo oxidation.
Received: 19 April 2001 / Accepted: 7 November 2001 / Published online: 23 January 2002 相似文献
18.
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 相似文献
19.
X.Y. Chen K.H. Wong C.L. Mak J.M. Liu X.B. Yin M. Wang Z.G. Liu 《Applied Physics A: Materials Science & Processing》2002,74(5):703-706
Selective growth of single-oriented (110), (100) and (111) MgO films on Si (100) substrates without buffer layers was obtained
via a two-step method by pulsed laser deposition. It was found that the orientation of the films was determined at the initial
deposition stage by the substrate temperature only. The ambient pressure during deposition, the laser fluence and the etching
of the Si substrates have no apparent effect on the orientation of the films, but affect their crystalline quality. Under
the present deposition conditions, the surfaces of all three different single-oriented films were very smooth and devoid of
any particulates.
Received: 23 January 2001 / Accepted: 6 June 2001 / Published online: 2 October 2001 相似文献
20.
J.C.S. Moraes A. Scalabrin M.D. Allen K.M. Evenson 《Applied physics. B, Lasers and optics》2002,74(6):541-543
Through the optical pump technique we have reinvestigated the CHD2OH molecule as a source of far-infrared (FIR) laser lines using for the first time a CO2 laser lasing on regular, hot, and sequence bands. As a consequence, we present here spectroscopic data of 16 new FIR laser
transitions from this molecule. Furthermore, we also present a catalogue of all FIR laser lines generated from CHD2OH.
Received: 13 July 2001 / Revised version: 25 October 2001 / Published online: 14 May 2002 相似文献