共查询到20条相似文献,搜索用时 31 毫秒
1.
Vogel N. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1999,27(4):864-871
The temporal evolution of X-ray emission of laser-induced discharges was investigated by means of a picosecond X-ray streak camera. Point-like structures with small divergence and thin hot layers of intense X-ray radiation with life time from 30 ps to 1.5 ns in a spectral range 100 eV-10 keV have been found in a comparatively low voltage vacuum discharge (U≈150 V-2.7 kV) initiated by picosecond laser beam. The radiation of laser induced breakdown was investigated just after breakdown as well as with a delay time (up to 20 ns) relative to the ignition point by the laser beam in order to eliminate the X-ray radiation coming from the laser-produced plasma 相似文献
2.
S. A. Pikuz A. Maksimchuk D. Umstadter M. Nantel I. Yu. Skobelev A. Ya. Faenov A. Osterheld 《JETP Letters》1997,66(7):480-486
Laser satellites are detected in the emission spectra of magnesium and aluminum plasmas produced by femtosecond laser pulses.
This is made possible by the realization of picosecond time resolution in a high-luminosity x-ray spectrograph with a spherically
curved mica crystal. The temporal characteristics of these newly recorded spectral lines show unequivocally that they are
formed as a result of nonlinear processes.
Pis’ma Zh. éksp. Teor. Fiz. 66, No. 7, 454–459 (10 October 1997) 相似文献
3.
A. É. Bugrov S. Yu. Gus’kov V. B. Rozanov I. N. Burdonskii V. V. Gavrilov A. Yu. Gol’tsov E. V. Zhuzhukalo N. G. Koval’skii V. N. Kondrashov M. I. Pergament V. M. Petryakov S. D. Tsoi 《Journal of Experimental and Theoretical Physics》1999,88(3):441-448
We have experimentally investigated the interaction of high-power neodymium laser pulses in the intensity range 1013–1014 W/cm2 with flat low-density (0.5–10 mg/cm3) agar-agar targets under conditions of interest for problems of inertial nuclear fusion. Optical and x-ray methods with high
temporal and spatial resolution were used to examine the dependence of absorption and scattering of the incident beam on the
initial mean density and thickness of the irradiated samples. We show that when a porous target is irradiated, a bulk absorption
layer of high-temperature plasma is produced inside the target whose dimensions are determined by the initial density of the
material. The time dependence and spectral composition of the harmonics 2ω
0 and 3ω
0/2 observed in the plasma-scattered radiation are measured. A theoretical model is developed that describes the interaction
of high-power laser pulses with a porous medium. Predictions of the model, based on the hypothesis of two stages of homogenization
of the target material—a fast stage (0.1–0.3 ns) and a slow stage (1–3 ns), are in good agreement with the experimental data.
Zh. éksp. Teor. Fiz. 115, 805–818 (March 1999) 相似文献
4.
S. Dobosz M. Schmidt M. Perdrix P. Meynadier O. Gobert D. Normand K. Ellert T. Blenski A. Ya. Faenov A. I. Magunov T. A. Pikuz I. Yu. Skobelev N. E. Andreev 《Journal of Experimental and Theoretical Physics》1999,88(6):1122-1129
The x-ray spectra of a plasma generated by heating CO2 and Ar clusters with high-intensity femtosecond laser pulses with q
las≃1018 W/cm2 are investigated. Spatially resolved x-ray spectra of a cluster plasma are obtained for the first time. Photoionization absorption
is observed to influence the spectral line profiles. The recorded features of the x-ray emission spectra definitely indicate
the existence of a large relative number of excited ions (≃10−2–10−3) with energies of 0.1–1 MeV in such a plasma. Possible mechanisms underlying the acceleration of ions to high energies are
discussed. It is shown that the experimental results can be attributed to the influence of ponderomotive forces in standing
waves generated by the reflection of laser radiation from the clusters.
Zh. éksp. Teor. Fiz. 115, 2051–2066 (June 1999) 相似文献
5.
The dynamics of a high-current (102–104 A) electron beam with energies of 105–106 eV and picosecond duration (10−10 s) at the output of the accelerator tube is investigated. The slowing of electrons by the residual positive charge on the
surface of the tube is found to have a significant influence in the case of short pulse durations. The distance of the electron
beam from the surface of the tube in vacuum is estimated on the basis of a one-dimensional model. It is shown that the electron
radiation can travel to a distance of several centimeters from the surface at current densities below 20 A/mm2, whereas at high current densities the beam is trapped near the surface.
Zh. Tekh. Fiz. 69, 111–115 (May 1999) 相似文献
6.
Temporal, spatial and spectral characteristics of a multi-keV monochromatic point x-ray source based on vacuum diode with
laser-produced plasma as cathode are presented. Electrons from a laser-produced aluminium plasma were accelerated towards
a conical point tip titanium anode to generate K-shell x-ray radiation. Approximately 1010 photons/pulse were generated in x-ray pulses of ∼18 to ∼28 ns duration from a source of ∼300 μm diameter, athυ = 4.51 keV (K
α emission of titanium), with a brightness of ∼1020 photons/cm2/s/sr. This was sufficient to record single-shot x-ray radiographs of physical objects on a DEF-5 x-ray film kept at a distance
of up to ∼10 cm. 相似文献
7.
A. G. Rousskikh A. V. Shishlov A. S. Zhigalin V. I. Oreshkin S. A. Chaikovsky R. B. Baksht 《Technical Physics》2010,55(11):1619-1627
The results of the experiments on the formation of a plasma emitter with small spatial dimensions for pulsed radiography in
the soft X-ray spectral range are presented. Emitting hot plasma was formed as a result of compression of the plasma jet by
a current pulse with amplitude I
m
= 215 kA and rise time T
fr = 200 ns. For the jet formation, we used a plasma gun based on the arc discharge (I
m
= 8.5 kA and T
fr = 6 μs) initiated by breakdown over the surface of a dielectric in vacuum. The experiments were carried out with aluminum,
tin, copper, and iron plasma jets. A single emitter, i.e., point Z-pinch (PZ-pinch), was formed when an interelectrode gap of a high current generator of 1.3–1.5 mm was used. The smallest spatial dimensions
of the emitting region were obtained with the use of aluminum and tin. For a tin jet, the diameter of the emitting region
was 7 ± 2 μm and its height was 17 ± 2 μm. The emission pulse duration at half-height was 2–3 ns. The total emission yield
per pulse in the spectral range 1.56–1.90 keV was 30–50 mJ for the aluminum pinch and 10–30 mJ for the tin pinch. The developed
method makes it possible to carry out radiographic examination of microobjects (including biological ones) 1–1000 μm in thickness,
with spatial (10–20 μm) and time (2–3 ns) resolution. 相似文献
8.
Amplified spontaneous inner-shell emission produced via an ultrafast burst of high-energy electrons from a femtosecond laser-produced
plasma is proposed as a novel electron-pumped x-ray laser. In this scheme, a population inversion of the upper laser level
is created via impact ionization of atomic inner shells by electron bombardment. Based on the requirement of a positive gain
coefficient for amplifying spontaneous K
α
line emission, a simple pumping threshold is found for the incident electron flux, and feasibility of the scheme is assessed
for a range of low-Z elements.
Published in English in the original Russian journal. Edited by Steve Torstveit.
Pis’ma Zh. éksp. Teor. Fiz. 67, No. 10, 771–776 (25 May 1998) 相似文献
9.
A. N. Chumakov S. A. Petrov N. A. Bosak E. N. Shcherbakova 《Journal of Applied Spectroscopy》2012,79(4):664-669
We have obtained carbon thin films on silicon and glass substrates with multipulse pulsed laser irradiation of graphite under vacuum (p ≈ 2.6 Pa) using a high-frequency series of nanosecond laser pulses (τ = 85 ns, λ = 1060 nm) with pulse repetition frequency f ≈ 10–20 kHz and laser power density q ≈ 15–40 MW/cm2. We established the optimal laser power density and laser pulse repetition frequency for obtaining amorphous nanostructured diamond-like films. 相似文献
10.
V K Senecha Y B S R Prasad M P Kamath A S Joshi G S Solanki A P Kulkarni S Gupta R Pareek H C Pant 《Pramana》2000,55(5-6):789-795
An investigation of x-ray emission from Cu plasma produced by 1.054 μm Nd:glass laser pulses of 5 ns duration, at 2 × 1012 − 2 × 1013 W cm−2 is reported. The x-ray emission has been studied as a function of target position with respect to the laser beam focus position.
It has been observed that x-ray emissions from ns duration plasma show a volume effect similar to subnanosecond plasmas. Due
to this effect the x-ray yield increases when target is moved away relative to the best focal plane of the laser beam. This
result supports the theoretical model of Tallents and has also been testified independently using suitably modified theoretical
model for our experimental conditions. While above result is in good agreement with similar experimental results obtained
for sub-nanosecond laser produced plasmas, it differs from result claiming filamentation rather than pure geometrical effect
leading to x-ray enhancement for ns plasmas. 相似文献
11.
Thomas Lehecka Andrew Mostovych Jeffrey Thomas 《Applied Physics A: Materials Science & Processing》2008,92(3):727-741
Time resolved emission from the interaction of ultra-short (∼200 fs) laser pulses with aluminum and copper targets was investigated.
Measurements show that emission from the laser produced plasma in air is significantly more intense than in near vacuum conditions
and that the emission in air can extend for periods exceeding 100 ns. Modeling the laser–target–air coupling shows that the
laser–target interaction can lead to blast wave shock waves being launched in the ambient air and that the emission from the
shocked air dominates over emission from the target surface. The long term emission measurements in air are in agreement with
the modeling results. 相似文献
12.
A. E. Bugrov S. Yu. Gus’kov V. B. Rozanov I. N. Burdonskii V. V. Gavrilov A. Yu. Gol’tsov E. V. Zhuzhukalo N. G. Koval’skii M. I. Pergament V. M. Petryakov 《Journal of Experimental and Theoretical Physics》1997,84(3):497-505
We have experimentally investigated the processes of laser light absorption and energy transfer in porous targets made of
“agar-agar” (C14H18O7) with an average density of 1–4 mg/cm3 illuminated by the focused beam of a neodymium laser with an intensity of 1014 W/cm2 within a pulse of duration 2.5 ns. Many important scientific and technical problems, e.g., inertial-confinement thermonuclear
fusion, the creation of lasers in the x-ray regime, and the modeling of astrophysical phenomena under laboratory conditions,
can be successfully addressed by using low-density porous media as components of such targets. In our experiments with porous
targets of variable density and thickness we used optical and x-ray diagnostic methods, which ensured that our measurements
were made with high temporal and spatial resolution. We show that a region forms within the porous target consisting of a
dense high-temperature plasma which effectively absorbs the laser radiation. Energy is transferred from the absorption region
to the surrounding layer of porous material at up to 2×107 cm/s. Experimental data are in good agreement with the predictions of our theoretical model, which takes into account the
specific features of absorption of laser radiation in a porous material and is based on representing the energy transfer within
the material as a hydrothermal wave.
Zh. éksp. Teor. Fiz. 111, 903–918 (March 1997) 相似文献
13.
R. P. Babertsyan É. S. Badalyan G. A. Egiazaryan É. I. Ter-Gevorkyan 《Technical Physics》1998,43(9):1035-1038
A steady-state Penning ion source is studied experimentally. Depending on the geometric parameter l
a
(the anode length to diameter ratio) and pressure, maxima are observed in the discharge current and in the ion beam current
extracted from an aperture at the center of the cathode. It is shown that at pressures of the order of 10−4 Torr, two maxima appear in these currents: one, for short discharge gaps with l
a
=1–1.5, corresponds to a diverging ion beam, and the other, for longer anodes with l
a
=4–5, to a collimated ion beam. At pressures of the order of 10−5 Torr, only one maximum appears in these currents, for short anodes l
a
=2–3 with a diverging ion beam. A physical explanation is proposed for these findings.
Zh. Tekh. Fiz. 68, 29–32 (September 1998) 相似文献
14.
The well-known defects of the surface of a solid, microscopic projections and spikes, play a decisive role in electron emission
induced by an electric field. If there are mobile electrons of holes in the solid, then the electric field is enhanced by
a factor of 10–100 at the tip of a microscopic projection. This effect was discovered in electrostatics more than a century
ago. In turn, the probability of tunnel emission of an electron from a metal into a vacuum is an exponential function of the
electric field strength. Correspondingly the electron emission current density at the tip of a microscopic spike can be larger
than that on a smooth surface by an astronomical factor. This effect is particularly strikingly manifested when picosecond
pulses of infrared laser radiation of moderate power are used to initiate autoelectronic emission. Relative to a smooth surface,
the emission current density is enhanced by hundreds of orders of magnitude. These experimental conditions can be used to
scan the surface of a conducting material with a laser beam and to detect all the microscopic projections, in order to male
detailed observations with subpicosecond time resolution of the phase transition from autoelectronic emission to explosive
emission.
Polytechnic University, Tomsk. Institute of Electrophysics, Ural Branch of the Russian Academy of Sciences. French National
Scientific Center, Saclay, France. Translated from Izvestiya Vysshikh Uchenbnykh Zavedenii, Fizika, No. 11, pp. 42–44, November,
1997. 相似文献
15.
S. Dobosz M. Schmidt M. Perdrix P. Meynadier O. Gobert D. Normand Ya. Faenov A. I. Magunov T. A. Pikuz I. Yu. Skobelev N. E. Andreev 《JETP Letters》1998,68(6):485-491
The x-ray spectra of a plasma produced by heating CO2 clusters with intense femtosecond laser pulses with λ=0.8 μm and λ=0.4 μm are investigated. Spatially resolved x-ray spectra
of the cluster plasma are obtained. The observed characteristic features of the x-ray emission spectra show unequivocally
that such a plasma contains quite a large relative number of ions (≃10−2–10−3) with energies of 0.1–1 MeV. The contour of the OVIII Lyα line is found to have characteristic features that are especially conspicuous when the clusters are heated with second-harmonic
pulses. These features cannot be explained by any mechanisms known to the authors.
Pis’ma Zh. éksp. Teor. Fiz. 68, No. 6, 454–459 (25 September 1998) 相似文献
16.
É. Yu. Khautiev P. S. Antsiferov L. A. Dorokhin K. N. Koshelev Yu. V. Sidel’nikov 《Technical Physics》1998,43(11):1373-1375
Experiments are described in which a plasma focus is used simultaneously as an inductive store and a current switch. The obtained
rates of current growth on a load of 0.01 Ω is 1012 A/s, and the maximum values of the switched current lie in the range 50–100 kA. The technique is seen as promising for employing
a capillary discharge as a source of laser medium for the soft x-ray region.
Zh. Tekh. Fiz. 68, 110–113 (November 1998) 相似文献
17.
Results are presented from the first stage of studies on the passage of an electron beam with energy 100–500 eV in a magnetic
field of 300–700 Oe through the curvilinear solenoid of the KRéL unit, the latter being a prototype of the closing segment
of the Drakon stellarator system, in the plasma-beam discharge regime. The ion density at the end of the curvilinear part
of the chamber, n
i
≈8×108–1010 cm−3, the electron temperature T
e
≈4–15 eV, and the positions at which the beam hits the target for different distances from it to the electron source are determined
experimentally. The motion of the electron beam is computationally modeled with allowance for the space charge created by
the beam and the secondary plasma. From a comparison of the experimentally measured trajectories and trajectories calculated
for different values of the space charge, we have obtained an estimate for the unneutralized ion density of the order of 5×107 cm−3.
Zh. Tekh. Fiz. 69, 22–26 (February 1999) 相似文献
18.
P. Urayama W. Zhong J.A. Beamish F.K. Minn R.D. Sloboda K.H. Dragnev E. Dmitrovsky M.-A. Mycek 《Applied physics. B, Lasers and optics》2003,76(5):483-496
This article describes the design and characterization of a wide-field, time-domain fluorescence lifetime imaging microscopy
(FLIM) system developed for picosecond time-resolved biological imaging. The system consists of a nitrogen-pumped dye laser
for UV–visible–NIR excitation (337.1–960 nm), an epi-illuminated microscope with UV compatible optics, and a time-gated intensified
CCD camera with an adjustable gate width (200 ps-10-3 s) for temporally resolved, single-photon detection of fluorescence decays with 9.6-bit intensity resolution and 1.4-μm spatial
resolution. Intensity measurements used for fluorescence decay calculations are reproducible to within 2%, achieved by synchronizing
the ICCD gate delay to the excitation laser pulse via a constant fraction optical discriminator and picosecond delay card.
A self-consistent FLIM system response model is presented, allowing for fluorescence lifetimes (0.6 ns) significantly smaller
than the FLIM system response (1.14 ns) to be determined to 3% of independently determined values. The FLIM system was able
to discriminate fluorescence lifetime differences of at least 50 ps. The spectral tunability and large temporal dynamic range
of the system are demonstrated by imaging in living human cells: UV-excited endogenous fluorescence from metabolic cofactors
(lifetime ∼1.4 ns); and 460-nm excited fluorescence from an exogenous oxygen-quenched ruthenium dye (lifetime ∼400 ns).
Received: 23 February 2003 / Published online: 22 May 2003
RID="*"
ID="*"Corresponding author. Fax: +1-734/9361-905, E-mail: mycek@umich.edu 相似文献
19.
Evolution of vacancy defects in the surface layers of a metal irradiated with a pulsed electron beam
The distribution of vacancy defects in the surface layers of α-Fe after irradiation with a high-current pulsed electron beam is studied experimentally by unique nuclear-physical methods
— low-energy positron annihilation, Rutherford backscattering (RBS), and proton-induced x-ray emission (PIXE). Regions with
low local density, which are sources of crater formation on the surface of the irradiated sample, are observed by scanning
a proton microbeam. Positron lifetime measurements reveal that as the electron beam power increases, nonequilibrium vacancies
tend to be captured by carbon impurity atoms.
Pis’ma Zh. éksp. Teor. Fiz. 65, No. 8, 618–622 (25 April 1997) 相似文献
20.
D. I. Vaisburd S. I. Tverdokhlebov T. A. Tukhfatullin 《Russian Physics Journal》1997,40(11):1064-1082
A dense pulsed electron beam and nanosecond pulse length has been used to inject negative electric charge into various dielectric
materials (single crystals, glasses, composites, plastics) for initiation of electron field emission from the dielectric into
a vacuum. It has been shown that upon reaching a critical electric field in the bulk and at the dielectric surface there is
intense critical electron emission. The local current density from the emission centers reaches a record value (for dielectrics)
of the order of 106 A/cm2. The emission occurs in the form of a single gigantic pulse. The measured amplitude of the emission current averaged over
the emitting surface is the same order of magnitude as the injected electron current: 10–1000 A. the emission current pulse
lages behind the current pulse of the primary electron beam injected into the sample. The delay time is in the range 1–20
nsec and decreases with increasing current density of the injected beam. Direct experimental evidence is found for intense
generation of carriers (band or quasifree electrons) in the near-surface layer of the dielectric in a strong electric field
due to the Frenkel-Poole effect and collisional ionization of traps, usually various donor levels. This process greatly strengthens
the field emission from the dielectric. It has been shown experimentally that the emission is nonuniform and is accompanied
by “point bursts” at the surface of the dielectric and ionized plasma spikes in the vacuum interval. These spikes are the
main reason that the transition of the field emission into “bursts” is critical, similar to the current which has been previously
observed in metals and semiconductors. However there are a number of substantial differences. For example the critical field
emission current density needed for the transition into “bursts” is three orders of magnitude less than for metals. If we
provide sufficient electron current at the surface or from the bulk of the dielectric to the emission centers, then the critical
emission is always accompanied by a vacuum discharge between the surface of the dielectric and a metallic collector. A detailed
computer model of the processes in the dielectric during injection of a high-density electron beam has been developed which
allows one to understand the complex physical pattern of the phenomenon.
Tomsk Polytechnic University. Institute of High-Current Electronics, Siberian Section, Russian Academy of Sciences. Translated
from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 45–67, November, 1997. 相似文献