共查询到20条相似文献,搜索用时 0 毫秒
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N. G. Semaltianos S. Logothetidis W. Perrie S. Romani R. J. Potter S. P. Edwardson P. French M. Sharp G. Dearden K. G. Watkins 《Journal of nanoparticle research》2010,12(2):573-580
Silicon nanoparticles were generated by femtosecond laser [387 nm, 180 fs, 1 kHz, pulse energy = 3.5 μJ (fluence = 0.8 J/cm2)] ablation of silicon in deionized water. Nanoparticles with diameters from ~5 up to ~200 nm were observed to be formed in
the colloidal solution. Their size distribution follows log-normal function with statistical median diameter of ≈20 nm. Longer
ablation time leads to a narrowing of the nanoparticle size distribution due to the interaction of the ablating laser beam
with the produced nanoparticles. Raman spectroscopy measurements confirm that the nanoparticles exhibit phonon quantum confinement
effects and indicate that under the present conditions of ablation they are partially amorphous. 相似文献
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The influence of temporal pulse shaping on plasma plume generated by ultrafast laser irradiation of aluminum is investigated. Time resolved plasma emission spectroscopy is coupled with a temporal shaping procedure in a closed loop. The ionic emission is enhanced relative to the neutral one via an adaptive optimization strategy. The plasma emission efficiency in case of optimized and ultrashort temporal shapes of the laser pulses are compared, evidencing an enhancement of the ionization degree of the plasma plume. Simplified temporal shapes of the femtosecond laser pulses are extracted from the optimized shape and their corresponding effect on laser induced plasma emission is discussed. 相似文献
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Z. Liu X. Lu Q. Liu S. Sun L. Li X. Liu B. Ding B. Hu 《Applied physics. B, Lasers and optics》2012,108(3):493-500
In this work, supercontinuum conical emission (SC CE) accompanying the filamentation of powerful ultrashort laser pulse in BK7 glass and fused silica is studied. The SC CE is controlled by the laser power density and the sample thickness, and the minimum SC CE cut-off wavelength is about 309?nm in the BK7 glass and 237?nm in the fused silica. The angular distributions of the SC CE in the wavelength range less than 510?nm are measured by using a new method, and it cannot be explained by the Cerenkov emission theory but the unabridged X-Waves solution theory. Meanwhile numerical simulations of the propagation of femtosecond laser pulse in sample are performed to provide theoretical support to our results. 相似文献
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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. 相似文献
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The energy absorption efficiency of high-intensity (~10^{16}W/cm^2) femtosecond laser pulses in a dense jet of large rare-gas clusters has been measured. Experimental results show that the energy absorption efficiency is strongly dependent on the cluster size and can be higher than 90%. The measurement of the ion energy indicates that the average ion energies of argon and xenon can be as high as 90 and 100keV, respectively. The dependence of the average energy of the ions on the cluster size is also measured. At comparatively low gas backing pressure, the average ion energies of argon and xenon increase with increasing gas backing pressure. The average ion energy of argon becomes saturated gradually with further increase of the gas backing pressure. For xenon, the average ion energy drops a little after the gas backing pressure exceeds 9 bar (3.2×10^5 atoms/cluster). The result showing the existence of a maximum average ion energy has been interpreted within the framework of the microplasma sphere model. 相似文献
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The determinist behavior of the femtosecond ablation process allows morphing features well under the diffraction limit by utilizing the thresholding effect, down to the nanometer scale. Because there are a vast range of applications where scaling down the size of the features is a major concern, we investigate the use of superresolving pupil plane filters. As is well known, these filters redistribute the focused optical intensity for a narrower bright spot and, as a trade-off, increase the sidelobes. However, this drawback can be rendered insignificant if all the outer optical power is kept under the determinist threshold value. Two types of pure absorbing binary filter have been tried, giving credence to a size reduction of the ablations in fused silica. 相似文献
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We consider the new mechanism of X-ray generation by clusters under irradiation by femtosecond laser pulses, the so-called collective photorecombination. We develop the theory of the photo-recombination of electrons that pass from atomic clusters at the outer ionization to the ground level of a homogeneously charged cluster. Such a cluster is considered to be a quantum potential well. The dipole approximation is inapplicable for this process. We conclude that X-ray photons in collective photorecombination on a charged cluster as a whole have an energy that is much larger than that for photorecombination on separate atomic ions inside the cluster. For a typical cluster of 2.25 × 106 electrons, with a radius R = 300 Å, and a number density of plasma electrons n e = 2 × 1022 cm?3, we find that at a 5% outer ionization of this cluster, the energy of hard X-ray photons is 7.2 keV. 相似文献
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A.V. Karabutov V.D. Frolov E.N. Loubnin A.V. Simakin G.A. Shafeev 《Applied Physics A: Materials Science & Processing》2003,76(3):413-416
Low-threshold field electron emission (FEE) is reported for periodic arrays of micro-tips produced by laser ablation of Si
wafers. The best samples show emission at threshold fields as low as 4–5 V/μm for n-type Si substrates and of 1–2 V/μm for
p-doped Si substrates, as measured with a flat-screen technique. Auger electron spectroscopy and X-ray electron spectroscopy
reveal island-like deviation of the SiO2 stoichiometry on the tip surfaces, with lateral dimensions of less than 100 nm. Microscopic studies using a special field-emission
STM show that the emission originates from well-conducting regions of sub-micron size. The experimental data suggest FEE from
the tip arrays by a geometric field enhancement of both the individual micro-tip and the narrow conducting channels in the
tip body.
Received: 3 May 2002 / Accepted: 1 July 2002 / Published online: 28 October 2002
RID="*"
ID="*"Corresponding author. Fax: +7-095/135-82-34, E-mail: shafeev@kapella.gpi.ru 相似文献
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Time-resolved emission spectroscopy was employed to detect excited species formed in the laser ablation of superconductor
Pb-Bi-Sr-Ca-Cu-O by an excimer laser at various background gas pressures.
A simple model has been created to explain the chemical kinetics of reactions in a plasma plume by its expansion. We explained
the time dependence of plasma emission on the wavelengths of lead, strontium and their oxides. For the purpose of this paper,
we determined reaction rates of lead deexcitation and the rate of recombination of Pb+ ion.
This work was supported by the Grant Agency of Charles University (Grant No. 28/97) and Grant Agency of Academy of Sciences
of the Czech Republic (Grant No. A4040708). 相似文献
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Lithographical laser ablation using femtosecond laser 总被引:1,自引:0,他引:1
Y. Nakata T. Okada M. Maeda 《Applied Physics A: Materials Science & Processing》2004,79(4-6):1481-1483
Lithographical laser ablation was demonstrated using a femtosecond laser with a lithographical optical system. In this method, a femtosecond laser beam passes through a mask and the pattern is imaged on a film by a coherent optical system. As a result, the film is lithographically ablated, and a micron-sized pattern can be generated in a single shot. The resolution of generation was 13 m, and the narrowest width of a generated line was about 4 m. Moreover, the system was applied to transmission gratings as masks, and nano-sized periodic structures such as nano-sized hole matrices and nano-meshes were generated in a single shot. PACS 52.38.Mf; 42.25.Hz; 42.82.Cr; 81.16.-c 相似文献
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在微介观诊断中往往因为空间限制,选择具有亮度高、单色性好、对比度强的特征谱线,而忽略了轫致辐射谱线。率先实验设计了特征谱线和轫致辐射谱线的双光谱诊断X射线光源的方法,在中国工程物理研究院“星光Ⅲ”激光装置飞秒激光束靶室上进行实验,激光功率密度大于1.6×1018 W/cm2,脉宽为30 fs,45°入射靶面。在入射靶前侧,设计了用于特征光谱成像的针孔成像光路,获得Cu纳米颗粒靶产生的特征X射线的焦斑图像,为76 μm,大于刃边方法测得半径为54 μm的焦斑。在靶后侧,设计了轫致辐射成像光路,利用PIX射线CCD获得2×5的圆形Ta组图像。实验表明,利用双光谱成像设计合理,适合微介观材料动态诊断,提高诊断效率。 相似文献
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Spatial distribution of high-energy electron emission from water plasmas produced by femtosecond laser pulses 总被引:1,自引:0,他引:1
Li YT Zhang J Sheng ZM Teng H Liang TJ Peng XY Lu X Li YJ Tang XW 《Physical review letters》2003,90(16):165002
High energy electrons emitted by water plasmas produced by a single or a multiple laser pulse are investigated. The multipulse mode greatly enhances the generation and the temperature of hot electrons. Directional emission of high energy electrons over 25 keV is observed in two symmetric directions with respect to the laser axis and at 46 degrees from the directions of the laser electric field. Two-dimensional particle-in-cell simulations reproduce well the experimental results and indicate that the acceleration mechanism of the high energy electrons is due mainly to the resonance absorption at the edge of the spherical droplets formed by the leading pulse. 相似文献
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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. 相似文献
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A. A. Ilyin E. B. Sokolova S. S. Golik O. A. Bukin K. A. Shmirko 《Journal of Applied Spectroscopy》2012,78(6):861-866
The spectral and temporal characteristics of plasmas produced by femtosecond laser pulses acting on seawater surfaces are
studied. The time dependence of the decay in the intensities of emission lines and the continuum are determined and the electron
density is estimated using the three-body recombination time. It is shown that an atomic line with a low excitation potential
is the most sensitive for femtosecond laser induced breakdown spectroscopy. 相似文献