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1.
A new mechanism of a “Coulomb explosion,” where ions are accelerated by the electric field separating charges at the magnetic
Debye radius r
B∼B/4πen
e, is proposed on the basis of a nonquasineutral model of electronic vortices in a magnetic field. It is shown by means of
numerical calculations that in the process of acceleration of the ions a collisionless shock wave, whose front has an effective
width of the order of δ∼r
B, determined by the breakdown of quasineutrality, is formed in a time of the order of ω
pi
−1
, where ωpi is the ion plasma frequency. The origin of such explosive dynamics is the formation of “holes” in the electron density at
characteristic times of the order of ω
pe
−1
(ωpe is the electronic plasma frequency) as a result of the generation of electronic vorticity by the Weibel instability of an
electromagnetic wave. Calculations for a laser pulse with intensity J∼6×1018 W/cm2 show that the ions expand in the radial direction with velocities up to 3.5×108 cm/s.
Pis’ma Zh. éksp. Teor. Fiz. 70, No. 10, 669–674 (25 November 1999) 相似文献
2.
Md. Salimullah R. R. Sharma V. K. Tripathi 《Applied Physics A: Materials Science & Processing》1981,25(3):361-365
Using the fluid model for the nonlinear response of ions, we have studied the nonlinear scattering of an electromagnetic ion
cyclotron wave off the ion acoustic wave in a plasma. The low frequency nonlinearity arises through the parallel ponderomotive
force on ions and the high frequency nonlinearity arises through the nonlinear current density of ions. For a typical nonisothermal
plasma (T
e/T
i∼10) the threshold for this instability in a uniform plasma is ∼1mW/cm2. At power densities ≳102 W/cm2, the growth rate for backscatter turns out to be ∼104s−1. 相似文献
3.
J. Hoffman W. Mróz A. Prokopiuk Z. Szymanski 《Applied Physics A: Materials Science & Processing》2008,92(4):921-926
The plasma plume induced during ArF laser ablation of a graphite target is studied. Velocities of the plasma expansion front
are determined by the optical time of flight method. Mass center velocities of the emitting atoms and ions are constant and
amount to 1.7×104 and 3.8×104 m s−1, respectively. Higher velocities of ions result probably from their acceleration in electrostatic field created by electron
emission prior to ion emission. The emission spectroscopy of the plasma plume is used to determine the electron densities
and temperatures at various distances from the target. The electron density is determined from the Stark broadening of the
Ca II and Ca I lines. It reaches a maximum of ∼9.5×1023 m−3 30 ns from the beginning of the laser pulse at the distance of 1.2 mm from the target and next decreases to ∼1.2×1022 m−3 at the distance of 7.6 mm from the target. The electron temperature is determined from the ratio of intensities of ionic
and atomic lines. Close to the target the electron temperature of ∼30 kK is found but it decreases quickly to 11.5 kK 4 mm
from the target. 相似文献
4.
E. Yu. Loktionov A. V. Ovchinnikov Yu. Yu. Protasov D. S. Sitnikov 《Bulletin of the Lebedev Physics Institute》2010,37(3):82-84
Optical gas-dynamic processes occurring in polymeric targets ((CH2O)
n
, (C2F4)
n
) exposed to ultrashort laser pulses (τ
0.5 ∼ 45 − 70 fs; λ
I,II,III
= 266, 400, 800 nm; and E/S ∼ 0.1 − 40 J/cm2 at r
0 ∼ 20 μm) were studied under normal conditions and in vacuum (p ∼ 10−2 Pa). The dynamics of the mass flow from the target surface (m′ ∼ 10−5 − 10−4 g/J) was studied and the spectral-energy thresholds of laser ablation, the electron density distribution (n
e
∼ 1014 − 1018 cm−3), the mass-averaged velocity of the material flow from the target surface (∼ 103 m/s), and the chemical composition and average temperature in the near-surface plasma formation (T ∼ 5000 K) were determined using interference microscopy, emission spectroscopy, and shadowgraphy. 相似文献
5.
V. D. Zvorykin A. O. Levchenko A. G. Molchanov I. V. Smetanin N. N. Ustinovskii 《Bulletin of the Lebedev Physics Institute》2010,37(2):60-64
The grazing mode of microwave propagation in a hollow plasma waveguide formed by ionization of atmospheric air with a small
easily ionized additive by strong UV pulses of the Garpun KrF laser (λ = 248 nm, the pulse duration and energy are ∼70 ns and ∼50 J) was experimentally demonstrated for the first time. The annular
laser beam produced a hollow tube ∼10 cm in diameter with an electron density of ∼1012 cm−3 in a plasma wall ∼1 cm thick, over whichmicrowave radiation with λ
mw
∼ 8 mm was transmitted to a distance of 60 m. Themicrowave signal transmitted by the waveguide was amplified by a factor
of 6 in comparison with propagation in free space. 相似文献
6.
A magnetized, low-β plasma in pure toroidal configuration is formed and extensively studied with ion mass as control parameter. Xenon, krypton
and argon plasmas are formed at a fixed toroidal magnetic field of 0.024 T, with a peak density of ∼1011 cm−3, ∼4 × 1010 cm −3 and ∼2 × 1010 cm −3 respectively. The experimental investigation of time-averaged plasma parameter reveals that their profiles remain insensitive
to ion mass and suggests that saturated slab equilibrium is obtained. Low-frequency (LF) coherent fluctuations (ω < ω
ci) are observed and identified as flute modes. Here ω
ci represents ion cyclotron frequency. Our results indicate that these modes get reduced with ion mass. The frequency of the
fluctuating mode decreases with increase in the ion mass. Further, an attempt has been made to discuss the theory of flute
modes to understand the relevance of some of our experimental observations. 相似文献
7.
8.
A 3.7 GHz system, which is meant for LHCD experiments on ADITYA tokamak, is used for producing ECR discharge. The ECR discharge
is produced by setting the appropriate resonance magnetic field of 0.13 T, with hydrogen at a fill pressure of about 5 × 10−5 Torr. The RF power, up to 10 kW (of which ∼50% is reflected back), with a typical pulse length of 50 ms, is injected into
the vacuum chamber of the ADITYA tokamak by a LHCD grill antenna and is used for plasma formation. The average coupled RF
power density (the RF power/a typical volume of the plasma) is estimated to be ∼5 kW/m3. When the ECR appears inside the tokamak chamber for the given pumping frequency (f = 3.7 GHz) a plasma with a density (n
e) ∼ 4 × 1016 m−3 and electron temperature ∼8 eV is produced. The density and temperature during the RF pulse are measured by sets of Langmuir
probes, located toroidally, on either side of the antenna. Hα signals are also monitored to detect ionization. An estimate of density and temperature based on simple theoretical calculation
agrees well with our experimental measurements. The plasma produced by the above mechanism is further used to characterize
the ECR-assisted low voltage Ohmic start-up discharges. During this part of the experiments, Ohmic plasma is formed using
capacitor banks. The plasma loop voltage is gradually decreased, till the discharge ceases to form. The same is repeated in
the presence of ECR-formed plasma (RF pre-ionization), formed 10 ms prior to the loop voltage. We have observed that (with
LHCD-induced) ECR-assisted Ohmic start-up discharges is reliably and repeatedly obtained with reduced loop voltage requirement
and breakdown time decreases substantially. The current ramp-up rates also decrease with reduced loop voltage operation. These
studies established that ECR plasma formed with LHCD system exhibits similar characteristics as reported earlier by dedicated
ECR systems. This experiment also addresses the issue of whether ECR plasma formed with grill antenna exhibits similar behavior
as that formed by single waveguide ECR antenna. Our experimental observations suggest that the characteristics of (LHCD system-induced)
ECR-assisted Ohmic start-up discharges show similar properties, reported earlier with normal ECR-assisted Ohmic start-up discharges
and hence LHCD system may be used as ECR system at reduced toroidal magnetic field for other applications like wall conditioning.
相似文献
9.
Luteolin and apigenin, extracted from Reseda luteola L., were spectrophotometrically and fluorimetrically studied. The spectra were investigated as a function of pH in methanol/water
solutions (1/2, v/v) in the 2–12 pH range. The absorption spectra markedly shifted to the red by increasing the pH. Three acid–base dissociation
steps were detected for luteolin (pK
a = 6.9; 8.6; 10.3) and two for apigenin (pK
a = 6.6; 9.3). Fluorescence emission was very weak or undetectable (Φ
F < 10−4) in acidic solution, but increased in intensity with increasing the pH. Both molecules exhibited a great propensity towards
complex formation with metal ions, with association constants on the order of 105–107 for the first complexation step; in the presence of excess Al3+ ions, multiple equilibria were detected. A marked fluorescence enhancement was observed upon complexation with Al3+ ions (Φ
F ∼ 1 for luteolin and ∼10−2 for apigenin). 相似文献
10.
J. Cousin W. Chen D. Bigourd M. Fourmentin S. Kassi 《Applied physics. B, Lasers and optics》2009,97(4):919-929
We report on the development of a field deployable compact laser instrument tunable over ∼232 cm−1 from 3.16 to 3.41 μm (2932.5–3164.5 cm−1) for chemical species monitoring at the ppb-level. The laser instrument is based on widely tunable continuous-wave difference-frequency
generation (DFG), pumped by two telecom-grade fiber lasers. DFG power of ∼0.3 mW near 3.3 μm with a spectral purity of ∼3.3
MHz was achieved by using moderate pumping powers: 408 mW at 1062 nm and 636 mW at 1570 nm. Spectroscopic performance of the
developed DFG-based instrument was evaluated with direct absorption spectra of ethylene at 3.23 μm (∼3094.31 cm−1). Absorption spectra of vapor-phase benzene near 3.28 μm (∼3043.82 cm−1) were recorded with Doppler-limited resolution. Line intensities of the most intense absorption lines of the ν
12 band near 3043.8 cm−1 were determined to support development of sensitive mid-infrared trace gas detection of benzene vapor in the atmosphere.
Detection of benzene vapor in air at different concentration levels has been performed for the first time using multi-pass
cell enhanced direct absorption spectroscopy at ∼3.28 μm with a minimum detectable concentration of 50 ppb (1σ). 相似文献
11.
《Il Nuovo Cimento C》1991,14(2):171-193
Summary The data recorded with the neutrino detectors at Mont Blanc, Kamioka, Baksan and with the gravitational-wave detectors in
Maryland and Rome have been analysed searching for correlations associated with SN 1987 A, without presuming or excluding
hypotheses for correlations due to neutrinos and gravitational waves. The statistical analysis has been based on a previous
analysis that showed a correlation among Maryland, Rome and Mont Blanc with a probability to be accidental less than 10−5. Independent correlations are found during a period of one or two hours, around the Mont Blanc 5ν burst (2h 52 min 36 s UT),
among the various sets of data: Mont Blanc-Baksan with a probability to be accidental of the order ofp∼4·10−3, Mont Blanc-Kamioka withp∼4·10−3, Maryland-Rome-Kamioka withp∼5·10−4, Maryland-Rome-Baksan withp∼5·10−2. It is remarkable that the events from all the neutrino detectors follow the signals from the g.w. detectors by a time of
the order of 1/2 or 1 s. At present we will not give a physical interpretation of the observed correlations which have strong
statistical significance.
Professor Edoardo Amaldi died on December 5, 1989. 相似文献
12.
G. K. Ivanov G. V. Golubkov S. V. Drygin I. E. Cherlina 《Journal of Experimental and Theoretical Physics》1997,84(5):888-892
Ionization and dissociation of diatomic molecules induced by a weak field (after preliminarily populating an intermediate
level) and by intense, linearly polarized monochromatic radiation have been studied. Field-induced mixing of rotational components
of various electronic-vibrational states of molecules (such as CO, NO, etc.) at field strength f∼10−4–10−5 atomic units can lead to migration among states with different angular momenta J. Therefore, ions with rotational momenta J
+ much higher than those prescribed by selection rules for three-photon absorption can be formed from molecules in the ground
state. The possibility of selective formation of ions with J
+≫1 and zero projection of the angular momentum on the polarization vector of the external electromagnetic radiation has been
investigated.
Zh. éksp. Teor. Fiz. 111, 1624–1632 (May 1997) 相似文献
13.
Y. B. Kale A. Ray R. D’Souza Q. V. Lawande B. N. Jagatap 《Applied physics. B, Lasers and optics》2010,100(3):505-514
We here present a comparative study of frequency stabilities of pump and probe lasers coupled at a frequency offset generated
by coherent photon-atom interaction. Pump-probe spectroscopy of the Λ configuration in D2 transition of cesium is carried out to obtain sub-natural (∼2 MHz) electromagnetically induced transparency (EIT) and sub-Doppler
(∼10 MHz) Autler-Townes (AT) resonance. The pump laser is locked on the saturated absorption spectrum (SAS, ∼13 MHz) and the
probe laser is successively stabilized on EIT and AT signals. Frequency stabilities of pump and probe lasers are calculated
in terms of Allan variance σ(2,τ) by using the frequency noise power spectrum. It is found that the frequency stability of the probe stabilized on EIT is
superior (σ∼2×10−13) to that of SAS locked pump laser (σ∼10−12), whereas the performance of the AT stabilized laser is inferior (σ∼6×10−12). This contrasting behavior is discussed in terms of the theme of conventional master-slave offset locking scheme and the
mechanisms underlying the EIT and sub-Doppler AT resonances in a Doppler broadened atomic medium. 相似文献
14.
A. Ya. Faenov S. A. Pikuz A. G. Zidkov I. Yu. Skobelev P. S. Komarov O. V. Chefonov S. V. Gasilov A. V. Ovchinnikov 《JETP Letters》2010,92(6):375-378
The characteristics of X rays of a laser plasma generated in the interaction of a femtosecond pulse with solid targets in
an air atmosphere have been investigated. It has been shown that the mechanism for the generation of X rays in the interaction
of short intense laser pulses with solid targets in a gas atmosphere is attributed to the generation of fast electrons in
the region of the filamentation of a laser pulse. It has been proven experimentally that under such conditions, the solid
target irradiated by laser radiation of even a low density of about 1015 W/cm2 very efficiently emits ∼10-keV photons. It has been shown theoretically that the maximum energy of accelerated electrons
can reach ɛmax ∼ 100–200 keV under these conditions. This means that the proposed method can provide characteristic radiation with the energy
of photons much higher than 10 keV. 相似文献
15.
M. L. Hamilton R. Peverall G. A. D. Ritchie L. J. Thornton J. H. van Helden 《Applied physics. B, Lasers and optics》2009,97(3):715-722
We have demonstrated the production of ∼1.9 μm near-infrared radiation by using difference frequency generation within a 5%
MgO doped PPLN crystal by coupling ∼735 nm radiation from a tunable external cavity diode laser with relatively high powered
532 nm radiation from both Nd:YVO3 and Nd:YAG lasers. The radiation produced is of low power, ∼15 μW, and was used in conjunction with the sensitivity enhancing
techniques of wavelength modulation spectroscopy (WMS) and cavity enhanced absorption spectroscopy (CEAS). Experiments were
carried out on rotationally resolved transitions in the combination bands of NH3 and CO2 in the 1.9 μm region. An α
min value of 3.6×10−6 cm−1 Hz−1/2 was achieved for WMS measurements on CO2. A comparable α
min value of 2.2×10−6 cm−1 Hz−1/2 was achieved for NH3 using CEAS. The low NIR power indicates that despite the level of MgO doping quoted for the crystal, under prolonged exposure
photorefractive damage has occurred. 相似文献
16.
Amin Abdolvand Robert W. Lloyd Marc J. J. Schmidt David J. Whitehead Zhu Liu Lin Li 《Applied Physics A: Materials Science & Processing》2009,95(2):447-452
We present results on the growth of highly organised, reproducible, periodic microstructure arrays on a stainless steel substrate
using multi-pulsed Nd:YAG (wavelength of 1064 nm, pulse duration of 7 ns, repetition rate of 25 kHz, beam quality factor of
M
2∼1.5) laser irradiation in standard atmospheric environment (room temperature and normal pressure) with laser spot diameter
of the target being ∼50 μm. The target surface was irradiated at laser fluence of ∼2.2 J/cm2 and intensity of ∼0.31×109 W/cm2, resulting in the controllable generation of arrays of microstructures with average periods ranging from ∼30 to ∼70 μm, depending
on the hatching overlap between the consecutive scans. The received tips of the structures were either below or at the level
of the original substrate surface, depending on the experimental conditions. The peculiarity of our work is on the utilised
approach for scanning the laser beam over the surface. A possible mechanism for the formation of the structures is proposed. 相似文献
17.
E. I. Lakhno E. I. Burmakin I. V. Korzun G. Sh. Shekhtman 《Physics of the Solid State》2012,54(3):504-507
The rubidium monoferrite RbFeO2-based solid solutions with the composition Rb2 − 2x
Fe2 − x
P
x
O4 have been synthesized, and their crystal structure and the temperature and concentration dependences of the total and electron
conductivities have been studied. The introduction of P5+ ions has been found to sharply decrease the electron conductivity that prevails in pure rubidium monoferrite and, at the
same time, to increase the ionic conductivity. The latter becomes dominant as the phosphorus concentration increases. The
maximum rubidium-cation conductivity of the materials under study is ∼3 × 10−2 S/cm at 300°C and ∼3 × 10−1 S/cm at 700°C. The results have been compared with the previously obtained data for similar solid solutions based on rubidium
monogallate and monoaluminate. 相似文献
18.
A fluorescence enhancement phenomenon in the europium (Eu)–Ofloxacin (OF)–Sodium Dodecyl Benzene Sulfonate (SDBS) fluorescence
system was observed when Gd3+ was added. The fluorescence intensity of the systems was measured (λ
ex/λ
em = 280/612 nm) at pH 7.8. Under optimum conditions, a linear relationship between the enhanced fluorescence intensity and
the Eu3+ concentration in the range of 5.0 × 10−10 ∼ 2.0 × 10−7 mol·L−1 was observed. The detection limit of Eu3+ was 1.46 × 10−10 mol·L−1 (S/N = 3). This method was used for the determination of trace amounts of europium in synthetic rare earth samples with satisfactory
results. In addition, the interaction mechanism is also studied. 相似文献
19.
H. Kuwahara 《Applied physics. B, Lasers and optics》1979,20(1):67-73
Intensity self-pulsation in cw semiconductor lasers has been analyzed by computer simulation assuming saturable absorbing
characteristics in the loss term of the rate equation. A loss decrease of about 1% due to the saturable absorber is capable
of generating self-pulsation. The theoretical pumping dependence of the self-pulsation frequency is consistent with the experimental
data. Reflected light in the range of 10−5∼10−3 reduces the self-pulsation. Reflected light of larger than 10−2, however, induces self pulsation whose frequency is locked with the round trip time. The contribution of spontaneous emission
in the range of 10−4∼10−3 also reduces the self-pulsation, while 10−6∼10−5 is ineffective. 相似文献
20.
Loktionov E. Yu. Ovchinnikov A. V. Protasov Yu. S. Protasov Yu. Yu. Sitnikov D. S. 《Optics and Spectroscopy》2012,112(4):631-637
The opto-mechanical characteristics, such as the specific mechanical recoil momentum, the specific impulse, and the energy
efficiency, of the laser ablation of flat polymer targets ((C2F4)
n
, (CH2O)
n
) have been determined experimentally for the first time for the case of excitation with femtosecond pulses (τ ∼ 45–70 fs)
of UV-IR (λ ∼ 266, 400, 800 nm) laser radiation (I
0 up to 1015 W/cm2) under normal atmospheric and vacuum (p ∼ 10−4 mbar) conditions. The efficiency of mechanical recoil momentum generation is analyzed for various regimes of the laser irradiation. 相似文献