共查询到20条相似文献,搜索用时 109 毫秒
1.
Philipp Reissaus Tomas Waldemarsson Jürgen Blum Dominik Clément Isabel Llamas Harald Mutschke Frank Giovane 《Journal of nanoparticle research》2006,8(5):693-703
In order to find reliable collector surfaces for the Mesospheric Aerosol – Genesis, Interaction and Composition (MAGIC) sounding rocket experiment, intended to collect atmospheric nanoparticles, the sticking efficiency of nanoparticles was measured on several targets of different materials. The nanoparticles were generated by a molecular beam apparatus in Jena, Germany, by laser ablation (Al2O3 particles, diameter 5–50 nm) and by laser pyrolysis (carbon particles, diameter 10–20 nm). In a vacuum environment (>10−5 mbar) the particles condensed from the gas phase, formed a particle beam, and were accelerated to ∼
∼1 km/s. The sticking efficiency on the target materials carbon, gold and grease was measured by a microbalance. Results demonstrate moderate to high sticking probabilities. Thus, the capture and retrieval of atmospheric nanoparticles was found to be quantitatively feasible. 相似文献
2.
S. Yu. Udovichenko 《Technical Physics》1998,43(8):974-977
The dynamics of charged particle beams under the influence of their self-magnetic field and an external magnetic field is
examined on the basis of equations for the trajectory of a boundary particle. A study is made of the change in the dynamics
of fast particles due to the influence of the electric field of the partially neutralized space charge of the beam, the stationary
electric field, and the field of the oscillations in the quasineutral beam plasma. Changes in the total beam energy caused
by the self-electric field and in the longitudinal velocity owing to the self-magnetic field are taken into account.
Zh. Tekh. Fiz. 68, 106–109 (August 1998) 相似文献
3.
N. Vogel 《JETP Letters》1998,67(9):647-654
The dynamics of x-ray emission from a low-voltage laser-induced discharge was studied with the aid of a picosecond x-ray streak
camera. Directed x-ray emission in the spectral range from 100 eV to 10 keV in the form of point sources and thin layers with
lifetimes ranging from 30 ps to 1 ns was observed in a low-voltage vacuum discharge (U=150 V) initiated by a picosecond laser beam. X-ray emission from a discharge was detected with a time delay (1–20 ns) relative
to ignition by the laser beam in order to prevent the radiation of the laser plasma from entering the detector. Detection
of directed x-ray emission in a low-voltage vacuum discharge is demonstrated.
Pis’ma Zh. éksp. Teor. Fiz. 67, No. 9, 622–627 (10 May 1998) 相似文献
4.
V. G. Shvedov A. S. Desyatnikov A. V. Rode Y. V. Izdebskaya W. Z. Krolikowski Y. S. Kivshar 《Applied Physics A: Materials Science & Processing》2010,100(2):327-331
In this paper we show that laser beams containing phase singularity can be used for trapping and guiding light-absorbing particles
in air. The experiments were performed with agglomerates of carbon nanoparticles with the size in the range 0.1–10 μm; the
typical cw laser power was of a few mW. The stability of open-air three-dimensional trapping was within ±2 μm in both the transverse
and the longitudinal directions. The particle position on the beams axis within the trap can be controlled by changing the
relative intensity of two beams. The distinguishing feature of the trapping strategy is that particles are trapped at the
intensity minimum of the beam, thus with minimum heating and intervention into the particle properties, which is important
for direct studies of particle properties and for air-trapping of living cells. 相似文献
5.
ABSTRACTWhen a pulsed laser gets tightly focused onto a target-liquid interface, plasma formation occurs which leads to nucleation of nanoparticles based on the choice of target and its affinity to the surrounding liquid. Here, we report the generation of Titanium Oxide nanoparticles at titanium–water interface from defocused diverging laser beam rather than from converging tightly focused beam. This is done to tackle the laser-induced fragmentation of ejected nanoparticles in the beam path which widens the nanoparticulate statistics as laser energy gets consumed by the nanoparticles thereby causing a reduction in the ablation efficiency of the target material. The use of diverging laser beam effectively takes most of the ablated species away from the beam path and improvises on the ablation phenomena with yield up to 4?mg/h. The utility of the derived nanoparticulates under such conditions is then checked from its photocatalytic activity which shows 70% photodegradation of environmental pollutants. 相似文献
6.
V. A. Maisheev 《Journal of Experimental and Theoretical Physics》1997,85(6):1102-1109
The head-on propagation of a beam of γ grays through the field of a laser wave is investigated. The optical properties of the laser wave (as a medium) are described
by the dielectric tensor. The refractive indices are determined, and the polarization characteristics of electromagnetic normal
modes capable of propagating in such a medium are investigated. Relations are derived to describe the variation of the initial
polarization and intensity of a γ-ray beam as it propagates in a laser field. The influence of laser intensity on the investigated process is discussed.
Zh. éksp. Teor. Fiz. 112, 2016–2029 (December 1997) 相似文献
7.
Gaofang Li Xin Xue Xian Lin Sannan Yuan Naiyun Tang Fenghong Chu Haoyang Cui Guohong Ma 《Applied Physics A: Materials Science & Processing》2014,114(1):45-50
The unique optical properties of nanoparticles are highly sensitive in respect to particle shapes, sizes, and localization on a sample. This demands for a fully controlled fabrication process. The use of femtosecond laser pulses to generate and transfer nanoparticles from a bulk target towards a collector substrate is a promising approach. This process allows a controlled fabrication of spherical nanoparticles with a very smooth surface. Several process parameters can be varied to achieve the desired nanoparticle characteristics. In this paper, the influence of two of these parameters, i.e. the applied pulse energy and the laser beam shape, on the generation of Si nanoparticles from a bulk Si target are studied in detail. By changing the laser intensity distribution on the target surface one can influence the dynamics of molten material inducing its flow to the edges or to the center of the focal spot. Due to this dynamics of molten material, a single femtosecond laser pulse with a Gaussian beam shape generates multiple spherical nanoparticles from a bulk Si target. The statistical properties of this process, with respect to number of generated nanoparticles and laser pulse energy are investigated. We demonstrate for the first time that a ring-shaped intensity distribution on the target surface results in the generation of a single silicon nanoparticle with a controllable size. Furthermore, the generated silicon nanoparticles presented in this paper show strong electric and magnetic dipole resonances in the visible and near-infrared spectral range. Theoretical simulations as well as optical scattering measurements of single silicon nanoparticles are discussed and compared. 相似文献
8.
J. L. Jiménez Pérez R. Gutierrez Fuentes J. F. Sanchez Ramirez A. Cruz-Orea 《The European physical journal. Special topics》2008,153(1):159-161
Dual beam thermal lens technique is used to determine the
thermal diffusivity of different solvents in presence of gold nanoparticles.
In this technique an Ar+ laser (wavelength 514 nm, power 40 mW) and
intensity stabilized He-Ne laser were used as the heating source and probe
beam respectively. The experimental results showed that thermal diffusivity
values of the studied solvents (water, ethanol and ethylene glycol (EG))
were enhanced by the presence of gold nanoparticles. 相似文献
9.
N. E. Andreev M. V. Chegotov L. M. Gorbunov 《Journal of Experimental and Theoretical Physics》1999,88(6):1066-1071
It is shown that the size of the focal spot has a substantial influence on the dynamics of Mandel’shtam-Brillouin induced
scattering (MBIS) for the laser beam power near critical for striction self-focusing. For small focal spots MBIS suppresses
self-focusing. An increase in the size of the focal spot leads to growth of the MBIS pulsations and the steady-state setup
time. For large enough focal spots MBIS arises in the form of regular intense spikes. Physical processes shaping the dynamics
of MBIS are discussed.
Zh. éksp. Teor. Fiz. 115, 1950–1960 (June 1999) 相似文献
10.
S. Suzuki H. Yamaguchi T. Ishigaki R. Sen H. Kataura W. Krätschmer Y. Achiba 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):369-372
Time evolution of emission by carbon nanoparticles generated with a laser furnace technique was investigated with a high-speed
video camera. Assuming blackbody radiation formula for small spherical particle, the internal temperature of these carbon
nanoparticles was determined as a function of time delay (Δt) after laser vaporization. It was found that the internal temperature of them drastically decreased at Δt < 400μs through collision with the surrounding rare gas inside the furnace. On the other hand, in particular laser vaporization
condition where yields of C60 and other higher fullerenes in the soot were found to be high, an increase in the blackbody emission intensity could be recognized
for longer wavelength ( 660 < λ < 830 nm) at Δt > 400μs. This finding suggests that a certain exothermic process related to the formation of C60 and other higher fullerenes should occur at Δt > 400μs inside the furnace. 相似文献
11.
H. Shu S.-Z. Fu X.-G. Huang M.-X. Ma J. Wu J.-J. Ye J.-H. He Y. Gu 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,44(2):367-370
Using the ninth laser beam (converted to 2ω) of
“Shenguang-II” laser facility and the beam smoothing technology of
lens-array [Appl. Opt. 25, 377 (1986); Phys. Plasmas. 9, 3201 (1995)],
a shock wave with 700 μm (the root-mean-square of
shock breakout time (RMS) RMS ≈ 6.32 ps) flat top was created. An Al-Al
four-step target was designed to do research on shock wave stability in an
Al target. And the shock stability experiment with the Al-Al four-step
target indicated that the shock wave steadily propagated in the Al target of
thickness of about 20–45 μm under the power density of ~ 1.0×1014 W/cm2. 相似文献
12.
Zemin Wang Xiaoyan Zeng Ming Ji Yong Liu 《Applied Physics A: Materials Science & Processing》2009,97(3):683-688
Two methods of preparing Fe nanoparticles at atmospheric pressure were conducted using pulsed laser ablation of a 0.5-mm-diameter
Fe wire and a bulk Fe target. Passivated α-Fe nanoparticles covered with a shell of γ-Fe2O3 were prepared at different process parameters. The influences of average laser power, repetition rate, pulse duration and
carrier-gas pressure on the mean particle size for two laser ablation methods were investigated, respectively. The results
show that the target size has a large effect on the nanoparticle preparation though we have the same range of laser process
parameters. Except the carrier-gas pressure, the influence of the laser parameters on the mean particle size is almost opposite
for the two laser ablation methods. Besides, the ablation mechanisms were discussed to understand the variation of mean particle
sizes with target size. 相似文献
13.
A.V. Simakin V.V. Voronov N.A. Kirichenko G.A. Shafeev 《Applied Physics A: Materials Science & Processing》2004,79(4-6):1127-1132
A review of results on nanoparticles formation is presented under laser ablation of Ag, Au, and Ti solids targets in liquid environments (H2O, C2H5OH, C2H4Cl2, etc.). X-ray diffractometry (XRD), UV-Vis optical transmission spectrometry, and high-resolution transmission electron microscopy (HRTEM) characterise the nanoparticles. The morphology of nanoparticles is studied as a function of both laser fluence and nature of the liquid. The evidence of an intermediate phase of Au-Ag alloy is presented under exposure of a mixture of individual nanoparticles to laser radiation. Self-influence of the beam of a femtosecond laser is discussed under the ablation of the Ag target in liquids under Ti:sapphire laser. The factors are discussed that determine the distribution function of particle size under laser ablation. The influence of laser parameters as well as the nature on the liquid on the properties of nanoparticles is elucidated. PACS 42.62.-b; 61.46.+w; 78.66.-w 相似文献
14.
15.
Spherical semiconductor nanoparticles (ZnS) were specially fabricated by an inexpensive chemical route. The scattering profile
of the nanoparticles was investigated by laser light scattering technique. A beam of polarized light from a diode laser (λ
0 ≈ 630 nm) was allowed to fall on the nanospheres embedded in flexible host matrix Polyvinyl Alcohol (PVA). The light scattered
from the samples were detected by means of analyzer mounted photodiode array from 10° to 170° in steps of 1°. Signals from
the detectors were interfaced with a high resolution data acquisition system and the whole experiment was carried out in differential
mode. Size of the nanoparticles was obtained by using Mie theory and verified by T-matrix approach. The results obtained agree with the XRD and TEM results.
相似文献
16.
A numerical simulation is made of the processes occurring in a plasma lens under conditions when the focusing of a relativistic
electron beam is strongly affected by the ionization of the residual gas in the lens region by the beam itself. The paraxial,
azimuthally symmetric, 1.5-dimensional, electrostatic kinetic model, taking account of plasma production, expansion of the
plasma electrons away from the beam region, and contraction of the ions toward the axis of the beam, was used for the calculation.
The dynamics of the formation of a focal spot is studied, and the size and position of the spot are determined as functions
of time for different values of the gas pressure, initial plasma density, and energy of the beam electrons.
Zh. Tekh. Fiz. 67, 90–94 (October 1997) 相似文献
17.
N. A. Inogamov S. I. Anisimov B. Retfeld 《Journal of Experimental and Theoretical Physics》1999,88(6):1143-1150
The problems studied in this paper involve the action of laser radiation or a particle beam on a condensed material. Such
an interaction produces a hot corona, and the recoil momentum accelerates the cold matter. In the coordinate frame tied to
the accelerated target, the acceleration is equivalent to the acceleration of gravity. For this reason, the density distribution
ρ is hydrostatic in the zeroth approximation. In this paper the structure of such a flow is studied for a two-phase equation
of state. It is shown that instead of a power-law density profile, which obtains for a constant specific-heat ratio, a complicated
distribution containing a region with a sharp variation of ρ arises. Similar characteristics of the density profile arise with isochoric heating of matter by an ultrashort laser pulse
and the subsequent expansion of the heated layer. The formation of a rarefaction wave and the interaction of oppositely propagating
rarefaction waves in a two-phase medium are studied. It is very important to take account of the two-phase nature of the material,
since conditions (p
a
∼1 Mbar) are often realized under which the foil material comes after expansion into the two-phase region of the phase diagram.
Zh. éksp. Teor. Fiz. 115, 2091–2105 (June 1999) 相似文献
18.
The temporal evolution of a long-pulse high-density electron beam in a high-power traveling-wave tube with a periodic magnetic
focusing system is investigated. The relation between the variation of the characteristics of the electron beam and ionization
of the residual gas and particles desorbed from the electrode surfaces is shown. A strong influence of the formation of the
collector plasma and the flux of ions from its surface on the beam dynamics is revealed. The effect of microwave fields in
the transport channel on the characteristics of the beam during its evolution is studied.
Zh. Tekh. Fiz. 67, 54–58 (December 1997) 相似文献
19.
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
20.
The modern approach to designing an injector for the driver of a two-beam accelerator is based on the use of a bunched electron
beam. The results of simulation and comparison of the processes leading to bunching of a relativistic electron beam in a free-electron
laser and in a traveling-wave tube at low electron beam energies are discussed. The simulation and existing experimental results
for bunching of an electron beam in a free-electron laser are compared.
Zh. Tekh. Fiz. 69, 98–102 (February 1999) 相似文献