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51.
由Q-开关Nd:YAG激光器产生的1.06μm、10ns的脉冲激光辐射大气中的铝靶所产生的等离子体发射光谱的研究结果。当作用在铝靶表面的功率密度在1.0×10 ̄9W/cm ̄2-1.4×10 ̄(10)W/cm ̄2范围时,测定了等离子体在200至880nm波长范围内的空间、时间分辨发射光谱。实验发现,等离子体中N ̄+离子的辐射谱线与连续辐射同时出现并一起消失,随激光强度的增加N ̄+离子密度以指数关系增加,在激光源方向N ̄+离子的运动速度为零。从靶表面逸出的热电子与氮原子碰撞及随后发生的级联电离过程是产生N ̄+离子和空气等离子体的原因。 相似文献
52.
S. Borodziuk A. Kasperczuk T. Pisarczyk S. Yu. Gus'kov J. Ullschmied E. Krousky K. Masek M. Pfeifer K. Rohlena J. Skala M. Kalal J. Limpouch P. Pisarczyk 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,41(2):311-317
Efficiency studies of laser driven thin metal disks
acceleration using the first harmonic (λ1=1.315 μm) of
the Prague Asterix Laser System (PALS) and subsequent craters creation
produced by collisions of these disks with massive targets are presented.
Several different disks made of aluminium and copper foils with diameters of
300 μm and 600 μm and thicknesses of 11 μm (Al) and 3.6 μ
m (Cu) were employed. Disks were placed at the distance of either 100 μ
m or 300 μm in front of aluminium massive targets. The following
irradiation conditions were used: the laser beam energy of 120 J, the focal
spot diameter of 200 μm, and the pulse duration of 0.4 ns (FWHM). A
three-frame interferometric system was employed to determine electron
density distributions in plasma corona. Shape and volume of craters were
obtained by crater replica technology and microscopy measurements. The aim
of these investigations was to analyse conditions leading to the most
effective energy transfer in the process of collision of the accelerated
disks with solid targets. The overall efficiency of these processes was
characterized by the volume of craters produced in such targets. 相似文献
53.
Li Yang Paul W. May Lei Yin James A. Smith Keith N. Rosser 《Journal of nanoparticle research》2007,9(6):1181-1185
Crystalline carbon nitride nanopowders and nanorods have been successfully synthesized at room temperature and pressure using
the novel technique of pulsed laser ablation of a graphite target in liquid ammonia solution. High-resolution transmission
electron microscopy (HRTEM), selected area electron diffraction (SAED), and Fourier transform infrared spectroscopy (FTIR)
were used to systematically study the morphology, nanostructure and chemical bonding. The experimental composition and structure
of the nanoparticles are consistent with the theoretical calculations for α-C3N4. After 2 h ablation the particles had a size distribution ∼8–12 nm, whereas after 5 h ablation the particles had grown into
nanorod-like structures with a crystalline C3N4 tip. A formation mechanism for these nanorods is proposed whereby nanoparticles are first synthesized via rapid formation
of an embryonic particle, followed by a slow growth, eventually leading to a one-dimensional nanorod structure. 相似文献
54.
55.
Excimer laser ablation at 308 nm has been used to texture the surfaces of a variety of materials of interest for optoelectronic and biotechnological applications. Using a range of pre- and post-processing methods, we are able to produce nano-, micro- and meso-scale features over large areas rapidly in materials such as crystalline Si, porous silicon and TiO2. Texturing of porous silicon leads to the growth of crystalline dendritic structures, which distinguishes them dramatically from the conical pillars formed from crystalline silicon. Regular arrays of Si microdots are formed by irradiating a Si surface pre-covered with a Cr thin film grating. Nano-crystalline porous TiO2 films are easily ablated or compacted with laser irradiation. However, at low enough laser fluence, surface roughening without complete loss of porosity is possible. 相似文献
56.
Nanoparticles were synthesized by irradiating a nickel target with femtosecond laser pulses in high vacuum, and subsequently analyzed. The proof-of-principle experiments aim to modify the size characteristics of the produced nanoparticles. For nickel it is found that: (i) ultraviolet laser pulses lead to a remarkable change in the nanoparticles size distribution with respect to visible laser pulses; (ii) irradiation of the femtosecond pulses induced ablation plume with a second, delayed ultraviolet laser pulse can change the size characteristics of the produced nanoparticles. 相似文献
57.
Recent studies demonstrated that the process to produce metal and oxide nanoparticles by laser ablation of consolidated microparticles is a convenient and energy-efficient way to prepare nanoparticles. In this work, the novel process is applied to nanoparticle synthesis in the liquid environment and the results are compared with those by the gas-phase process. Metal and oxide nanoparticles are synthesized by pulsed laser ablation of the compacted metal microparticles using a Q-switched Nd:YAG laser in water. It is shown that the process is effective for preparing nanoparticle suspensions having relatively uniform size distributions. While the laser fluence and the degree of compaction strongly influence the size of the produced nanoparticle in air, the sedimentation time is shown to be the most critical factor to determine the mean size of the suspended particles. 相似文献
58.
Polydiphenylsilylenemethylene (PDPhSM) thin films, which are difficult to fabricate by conventional methods because of their insolubility and high melting point, have been synthesized by using laser-ablated metal nanoparticles for the thermal ring-opening polymerization of 1,1,3,3-tetraphenyl-1,3-disilacyclobutane (TPDC) in this paper. TPDC was first evaporated on silicon substrates and then exposed to metal (Pt, Cu and Ag) nanoparticles deposition by laser ablation prior to heat treatment. The catalytic activity of Pt, Cu and Ag nanoparticles has been studied. The results showed that the mean diameter of Pt nanoparticles was the smallest, Cu nanoparticles the moderate and Ag nanoparticles the biggest, while the polymerization efficiency for Pt nanoparticles was the highest, Cu nanoparticles the moderate and Ag nanoparticles the lowest. In addition, the penetration behaviours of Pt, Cu and Ag nanoparticles into the TPDC monomer films during laser ablation were different due to the particle size or the chemical interaction between metal nanoparticles and TPDC molecules. 相似文献
59.
The mass Δm removed per pulse in laser ablation was shown to correlate with the acoustic signal A and the beam diameter ?. The functional forms of Δm(A, ?) were deduced for aluminum and polyvinyl chloride, for fluence ranging from 1.5 through 88 J cm− 2. Δm so computed agreed with empirical values within experimental error. For samples whose mass is sensitive to environmental factors, off-line measurement of Δm was shown to be unreliable and real-time measurements such as acoustic monitoring became essential. 相似文献
60.
We demonstrate the nanosecond time-gated spectroscopy of plume luminescence in UV laser ablation of human hair. Clear and sharp peaks of calcium ion (Ca+) appear in the spectrum although the Ca content is only 0.1% in human hair. Highly sensitive detection of Ca is thus possible. In the experiment, the peak intensity of Ca+ was measured for human hair samples of female subjects over a wide range of age, and compared to the bone mineral density of the lumbar vertebrae of the subjects themselves. Our experimental results suggest that this specific spectroscopy has the potential for novel diagnoses including monitoring of daily Ca intake and a screening diagnosis of osteoporosis. The spectroscopic system and time transition of plume-luminescence spectra are also described. 相似文献