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101.
We report on the dynamical expansion of pulsed laser ablation of aluminum in ambient pressure of nitrogen using images of the expanding plasma. The plasma follows shock model at pressures of 0.1 Torr and drag model at 70 Torr, respectively, with incident laser energy of 265 mJ. The plasma expansion shows unstable boundaries at 70 Torr and is attributed to Rayleigh-Taylor instability. The growth time of Rayleigh-Taylor instability is estimated between 0.09 and 4 μs when the pressure is varied from 1 to 70 Torr. The pressure gradients at the plasma-gas interface gives rise to self-generated magnetic field and is estimated to be 26 kG at 1 Torr ambient pressure using the image of the expanding plasma near the focal spot. The varying degree of polarization of Al III transition 4s 2S1/2-4p 2P°3/2 at 569.6 nm gives rise to anisotropic emission and is attributed to the self-generated magnetic field that results in the splitting of the energy levels and subsequent recombination of plasma leading to the population imbalance. 相似文献
102.
Minimization of energy consumed in plasma generation is critical for applications, in which a large volume of plasmas is needed. We suggest that a high electron density atmospheric pressure plasmas can be generated by pulsed discharges in potassium seeded argon at an elevated temperature with a very small power input. The ionization efficiency and power budget of pulsed discharges in such plasmas are analytically studied. The results show that ionization efficiency of argon, especially at small reduced electric field E/N (the ratio of the electric field to the gas number density), is improved effectively in the presence of small amount of potassium additives. Power input of pulsed discharge to sustain a prescribed average level of ionization in potassium seeded argon is three orders of magnitude lower than that in pure argon. Further, unlike in pure argon, it is found that very short high-voltage pulses with very high repetition rates are unnecessary in potassium seeded argon. A pulse with lOOns of pulse duration, 5kHz of repetition rate, and 2Td (1 Td = 1 × 10^-21 Vm^2) of E/N is enough to sustain an electron density of 10^19 m^-3 in 1 arm 1500K Ar+0.1% K mixture, with a very small power input of about 0.08 × 10^4 W/m^3. 相似文献
103.
By using the concept of concurrence, we numerically investigate the thermal entanglement between any two nearest-neighbour spins in uniform and periodic anisotropic XY chains in a transverse field at finite temperature T. It is found that the entanglement has more than one critical temperatures on some parameter regions for uniform and periodic chains. We also discuss the behaviour of the thermal entanglement at the vicinity of quantum phase transition of periodic anisotropic XY chains and find that a11 the derivatives aλC have similar behaviour as that of the uniform chain. 相似文献
104.
M. K. Mishra A. Phukan M. Chakraborty K. S. Goswami 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2008,46(2):303-306
This paper reports about the observed energy growth of
both high and low energetic electron species in the target plasma region
with the increase in plasma potential in the source region of a double
plasma device. This situation can be correlated to the injection of an ion
beam from source to target plasma region. Plasma is solely produced in the
source region and a low-density diffuse plasma is generated in the target
region by local ionization between the neutral gas and the high energetic
electrons coming from the source region. The growth of electron energy is
accompanied by a decrease in diffuse plasma density. It is observed that
although energy of high energetic group increases with the injected beam
energy, the diffuse plasma density falls due to their decreasing population. 相似文献
105.
Y. Zhou G.-F. Zhang 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2008,47(2):227-231
We study quantum teleportation via a two-qubit Heisenberg
XXZ chain under an inhomogeneous magnetic field. We first consider entanglement
teleportation, and then focus on the teleportation fidelity under different
conditions. The effects of anisotropy and the magnetic field, both uniform
and inhomogeneous, are discussed. We also find that, though entanglement
teleportation does require an entangled quantum channel, a nonzero critical
value of minimum entanglement is not always necessary. 相似文献
106.
In this Letter, we have calculated the concurrence of the pairwise thermal entanglement for the four-qubit and five-qubit Heisenberg XX chain. It is found that there is a great difference between the even-qubit and the odd-qubit chain in the aspect of the critical temperature and of the existence of the entanglement for the case of the qubit number n no more than 5. 相似文献
107.
A.?Senchuk H.?P.?Kunkel R.?M.?RoshkoEmail author C.?Viddal Li?Wei G.?Williams X.?Z.?Zhou 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,34(3):285-292
Large spin systems as given by magnetic macromolecules or two-dimensional spin arrays rule out an exact diagonalization of
the Hamiltonian. Nevertheless, it is possible to derive upper and lower bounds of the minimal energies, i.e. the smallest energies for a given total spin S. The energy bounds are derived under additional assumptions on the topology of the coupling between the spins. The upper
bound follows from “n-cyclicity", which roughly means that the graph of interactions can be wrapped round a ring with n vertices. The lower bound improves earlier results and follows from “n-homogeneity", i.e. from the assumption that the set of spins can be decomposed into n subsets where the interactions inside and between spins of different subsets fulfill certain homogeneity conditions. Many
Heisenberg spin systems comply with both concepts such that both bounds are available. By investigating small systems which
can be numerically diagonalized we find that the upper bounds are considerably closer to the true minimal energies than the
lower ones.
Received 22 October 2002 / Received in final form 4 April 2003 Published online 20 June 2003
RID="a"
ID="a"e-mail: jschnack@uos.de 相似文献
108.
M.?PellarinEmail author E.?Cottancin J.?Lermé J.L.?Vialle M.?Broyer F.?Tournus B.?Masenelli P.?Mélinon 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,25(1):31-40
At the Prague Asterix Laser System Center (PALS) the Asterix iodine laser delivering up to 700 J/0.5 ns is used as a pump
source for X-ray laser experiments and applications. The prepulse technique was applied which is known to improve the neon-like
X-ray laser output at the J = 0-1 transition dramatically. Since Zn slab targets were used the operating wavelength was 21.2 nm. A prepulse having up
to 20 J precedes the main pulse by 10 ns. The main beam and the prepulse beam are focussed by two different optical systems
separately and their foci are superimposed at the target surface. By implementing a half-cavity set-up for double-pass amplification
using a Mo/Si multilayer mirror - which can be used for more than 100 shots - the X-ray laser output was more than 10 times
stronger than at the single pass in a 30 mm long plasma. Double-pass amplification was observed to be most efficient when
the pump pulse duration was at least 150 ps longer than the round trip time ( ≈ 260 ps) in the half-cavity. Under this fundamental
condition the X-ray laser reached saturation in the double-pass regime containing approx. 4 mJ energy which has been proved
to be enough for future applications. In this contribution, the X-ray laser features like divergence in two dimensions, the
beam quality (symmetry), the pointing angle and the integrated intensity giving an estimation of the output energy are investigated
over 110 shots. To characterize the stability of the X-ray laser the shot distribution, the mean value and the standard deviation
for these parameters are evaluated. For 18 shots in a series - what was achievable during one day - the corresponding values
are given, and a statistical analysis carrying out a chi-squared test characterize the Zn X-ray laser as a robust tool suitable
for applications. In the future it is planned to allocate X-ray laser beam time to external research groups.
Received 17 May 2002 / Received in final form 10 September 2002 Published online 6 November 2002
RID="a"
ID="a"e-mail: praeg@fzu.cz 相似文献
109.
Laser plasma thruster 总被引:5,自引:0,他引:5
Luke J.R. Phipps C.R. McDuff G.G. 《Applied Physics A: Materials Science & Processing》2003,77(2):343-348
The laser plasma thruster (LPT) is a new microthruster for small satellites. We report on development and testing of a prototype
LPT. Some advantages of the LPT are: thruster voltage 4 V, mass less than 1 kg, power-to-thrust ratio 10 kW/N, and Isp up to 1000 s. Typical thrust level is 250 μN with PVC fuel. Thrust of 1 mN is expected with energetic fuel. The pre-prototype
continuous-thrust experiment includes the laser mount and heat sink, lens mounts, and focusing mechanism, which are coupled
to the target-material transport mechanism. The target material is applied to a transparent plastic tape, and the laser is
focused on a series of tracks on the tape. The tape-drive hardware and laser-drive electronics are described. Design, construction,
and calibration of the thrust stand are described. During continuous operation, the exhaust plume is deflected in the direction
of the moving tape. When the laser is operated in pulsed mode, the exhaust plume is perpendicular to the tape (parallel to
the optical axis). This provides some thrust-vector control. Measured thrust is 70 μN with PVC fuel, and 550 μN with energetic
fuel, with a specific impulse of 350 s.
Received: 7 October 2002 / Accepted: 20 January 2003 / Published online: 28 May 2003
RID="*"
ID="*"Corresponding author. Fax: +1-505-272-7203, E-mail: luke@iera.nmt.edu 相似文献
110.
Parra E. McNaught S.J. Fan J. Milchberg H.M. 《Applied Physics A: Materials Science & Processing》2003,77(2):317-323
The interaction of high intensity 100-ps laser pulses with micron-sized noble gas (argon and krypton) droplets is experimentally
investigated via a series of pump–probe experiments monitoring the delay-dependent X-ray and extreme ultraviolet (EUV) emission,
and by imaging frequency-doubled probe light scattered from the interaction region. An understanding of the time scales for
this interaction is important for optimization of EUV sources for next-generation lithography that utilizes laser-produced
plasmas (LPP). Depending on the spectral region of interest, the type of emission, and the droplet characteristics, the effective
emission lifetime was found to extend from a few hundred picoseconds to as long as several nanoseconds, in agreement with
the expected plasma expansion, EUV excitation, and recombination emission time scales.
Received: 22 August 2002 / Accepted: 8 February 2003 / Published online: 28 May 2003
RID="*"
ID="*"Corresponding author. Fax: +1-301/3149-363, E-mail: riq@wam.umd.edu 相似文献