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1.
Li Tszen’ Fen’ G. E. Remnev M. S. Saltymakov V. I. Gusel’nikov V. A. Makeev I. V. Ivonin E. P. Naiden V. I. Yurchenko 《Russian Physics Journal》2007,50(1):66-70
The results of examination of the GaAs-target erosion under irradiation by a high-power pulsed ion beam are reported. In the experiments, use was made of a high-power
pulsed ion source with the following parameters: ion energy — 250 keV, target current density — 350 A/cm2, pulse duration — 80 ns, target energy density — up to 7 J/cm2. The target erosion coefficient and its dependence on the number of successive pulses are measured. It is found that the
surface roughness parameter is increased with the number of successive beam pulses. A regular structure of surface relief
is observed to form in the case where the number of pulses > 20–40.
__________
Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 66–70, January, 2007. 相似文献
2.
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
3.
A mechanism acceleration of electrons to relativistic velocities in a thin metal film irradiated with ultrashort (τ
L
≤1 ps) high-power (I>16 W/cm2) laser pulses is proposed. The acceleration is due to a resonance action of the nonuniform field on a portion of the electrons,
viz., those which oscillate in the direction transverse to the film with a frequency close to the frequency of the field.
Pis’ma Zh. éksp. Teor. Fiz. 66, No. 1, 8–12 (10 July 1997) 相似文献
4.
An experimental study is presented on measurements of optical spectrum of the laser light scattered from solid surface irradiated
by Ti:sapphire laser pulses up to an intensity of 1.2 × 1018 W cm−2. The spectrum has well-defined peaks at wavelengths corresponding to 2ω and 3/2ω radiations. The spectral features vary with the laser intensity and show blue-shift with increasing laser intensity. At a
constant laser fluence, the spectrum is red-shifted with increasing laser pulse duration. The observed results are explained
in terms of the density scale length variation of the plasma and laser chirp. 相似文献
5.
A simple electromagnetic transport system was constructed to identify very rare positrons produced in a powerful laser beam
interaction with a target. Testing experiments were carried out with CO2-laser (1012 W/cm2) beam pulses (τ=50 ns,f=0.01 Hz) focused on the copper target, as well as with a 96 MeV alpha-particle beam irradiated carbon target. The results
showed that the developed system could be effectively used for positron identification and evaluation of their energy by means
of a time-of-flight method. The computerized system to deal with this problem, together with others related to the power laser
beam interaction with targets, has been constructed. 相似文献
6.
A method has been proposed to analyze the dynamics of interband two-photon absorption in a nonlinear medium excited by a sequence
of picosecond laser pulses of variable intensity and continuous probe radiation. Induced absorption leading both to hysteresis
in the dependence of the absorption on the intensity of laser pump radiation and to the opacity of crystals at the pump wavelength
has been revealed in initially transparent ZnWO4 and PbWO4 crystals irradiated by a train of 523.5-nm pulses with a duration of 20 ps at pump intensities of 5 to 140 GW/cm2. The kinetics of an increase in absorption and its subsequent relaxation at a 523.5-nm picosecond excitation of the crystals
have been measured with continuous 633-nm probe radiation. An exponential component of the increase in absorption with the
time constant τ = 2−3.5 and 8–9.5 μs depending on the direction of the linear polarization of pump radiation has been revealed
at 300 K in ZnWO4 and PbWO4 crystals, respectively. The absorption relaxation kinetics in the crystals are complicated and approach an exponential at
a late stage with the constant τ = 40−130 and 12–80 ms for the ZnWO4 and PbWO4 crystals, respectively. 相似文献
7.
L. Palladino A. Reale G. Taglieri D. Batani S. Bollanti P. Di Lazzaro F. Flora T. Letardi G. Schina M. Belli A. Scafati 《Il Nuovo Cimento D》1993,15(8):1133-1146
Summary We present a detailed study of XUV and soft X-ray emission from Cu plasma produced by an excimer laser at intensitiesI
L≦8·1011 W/cm2. The XeCl excimer laser (ψ≈308 nm) delivers pulses with energyE
L≈2.3 J, temporal durationt
L≈100 ns and brightnessB≧1014 W/cm2 sr. We recorded a spectral conversion efficiency η=0.5% eV−1 forI
L=4·1011W/cm2 in the aluminium window at 73eV with a harder X-ray tail around ≈400eV. We also measured the dependence of X-ray signal on
laser intensity and viewing angle. Experimental results have been compared with some analytical laser-plasma interaction models. 相似文献
8.
J. Marczak K. Jach R. ?wierczyński 《Applied Physics A: Materials Science & Processing》2010,100(3):725-731
The interaction of laser radiation with matter leads to the certain kinds of modelling of its surface or volume. These effects
have been demonstrated for a lot of materials, even causing the formation of new scientific and industrial domain, which is
undoubtedly laser material processing and as well as laser cleaning of artworks. Those applications lie in the so-called “low'
region of laser energy densities, represented for short laser pulses by power densities below 109 W/cm2. Paper presents set of equations describing in one-dimensional (1D) model phenomena accompanying to laser–matter interaction.
Target geometry includes two and four layers of different materials, irradiated by ns laser pulses. Effects of radiation absorption
and transport, heat conductivity, target transit to plastic state, melting and evaporation are taken into consideration. The
part of the paper is devoted to the discussion of numerical results, selected in such a way to illustrate the phenomenon of
radiation interaction with materials as well as to show, in whole, possibilities of computer simulation methods. 相似文献
9.
We describe a new technique to measure the UV/visible absorption spectrum of the ablated material during the laser pulse.
The technique utilizes the continuum emission from one laser produced plasma as a light source to measure the absorption properties
of a second laser produced plasma which is formed on a semi-transparent target with an array of 40 μm holes. A 6 ns, 1064
nm laser was used to ablate a Ag target and the plasma absorption was measured in the range 450–625 nm for a laser fluence
of 1 J cm−2. The total absorption cross-section is (0.5–1.5)×10−17 cm2 in the range 450–540 nm. By comparing the measured absorption with a calculation using the plasma spectroscopy code FLYCHK
it can be concluded that, in the wavelength region examined here, the absorption is mainly due to bound-bound transitions. 相似文献
10.
B. Hopp G. Kecskeméti T. Smausz T. Ajtai A. Filep N. Utry A. Kohut Z. Bozóki G. Szabó 《Applied Physics A: Materials Science & Processing》2012,107(2):429-435
Preparation of organic thin layers on various special substrates using the pulsed laser deposition (PLD) technique is an important
task from the point of view of bioengineering and biosensor technologies. Earlier studies demonstrated that particle ejection
starts during the ablating laser pulse resulting in significant shielding effects which can influence the real fluence on
the target surface and consequently the efficiency of layer preparation. In this study, we introduce a photoacoustic absorption
measurement technique for in-situ characterization of ablated particles during PLD experiments. A KrF excimer laser beam (λ=248 nm, FWHM=18 ns) was focused onto pepsin targets in a PLD chamber; the applied laser fluences were 440 and 660 mJ/cm2. We determined the wavelength dependence of optical absorption and mass specific absorption coefficient of laser ablation
generated pepsin aerosols in the UV–VIS–NIR range. On the basis of our measurements, we calculated the absorbance at the ablating
laser wavelength, too. We demonstrated that when the laser ablation generated pepsin aerosols spread through the whole PLD
chamber the effect of absorptivity is negligible for the subsequent pulses. However, the interaction of the laser pulse and
the just formed particle cloud generated by the same pulse is more significant. 相似文献
11.
The particle size distribution, morphology and optical properties of the Au nanoparticle (NP) structures for surface enhanced
Raman signal (SERS) application are investigated in dependence on their preparation conditions. The structures are produced
from relatively thin Au films (10–20 nm) sputtered on fused silica glass substrate and irradiated with several pulses (6 ns)
of laser radiation at 266 nm and at fluencies in the range of 160–412 mJ/cm2. The SEM inspection reveals nearly homogeneously distributed, spherical gold particles. Their initial size distribution of
the range of 20–60 nm broadens towards larger particle diameters with prolonged irradiation. This is accompanied by an increase
in the uncovered surface of the glass substrate and no particle removal is observed. In the absorption profiles of the nanostructures,
the broad peak centred at 546 nm is ascribed to resonant absorption of surface plasmons (SPR). The peak position, halfwidth
and intensity depend on the shape, size and size distribution of the nanostructured particles in agreement with literature.
From peak intensities of the Raman spectra recorded for Rhodamine 6G in the range of 300–1800 cm−1, the relative signal enhancement by factor between 20 and 603 for individual peaks is estimated. The results confirm that
the obtained structures can be applied for SERS measurements and sensing. 相似文献
12.
A. Caruso N. N. Demchenko V. V. Demchenko S. G. Garanin V. V. Gavrilov A. Yu. Gol'tsov A. I. Gromov S. Yu. Gus'kov Yu. S. Kas'yanov G. A. Kirillov V. N. Kondrashov N. G. Koval'skii I. G. Lebo Yu. A. Merkul'ev V. V. Nikishin V. B. Rozanov A. A. Rupasov R. V. Stepanov C. Strangio S. A. Sukharev V. F. Tishkin G. A. Vergunova N. V. Zmitrenko 《Journal of Russian Laser Research》2000,21(4):335-369
The paper is devoted to recent results concerning investigation of physical processes occurring in a “laser greenhouse” target.
Results of experimental and theoretical studies of laser-pulse interaction with a low-density absorber of the target, namely,
with a porous substance having density close to the plasma critical density, are presented. On the basis of a vast cycle of
experiments carried out in a number of laboratories, it is shown that the absorption of the laser radiation in porous media,
including those with a density exceeding the critical one by at least a factor of 4 to 6, has a bulk nature and is distributed
over the target depth. In particular, the laser-radiation absorption region in a porous substance with density 10−3–10−2 g/cm3 is extended into the target 400–100 μm, respectively. The coefficient of absorption of laser radiation with intensity 1014–1015 W/cm2 in porous substances, including those of the supercritical density, is 70–90%. Experiments have not shown enhanced (compared
to a solid-state target) radiation intensity associated with a possible development of parametric instabilities in an extended
laser plasma of low-density porous media, as well as noticeable contribution of fast electrons to the energy balance and their
effect on the energy transfer. In this paper, theoretical models are developed explaining features of the laser-radiation
absorption and energy transfer in porous media. These models are based on the phenomenon of laser-radiation interaction with
solid components of a porous substance and plasma production inside pores and cells of the medium. The efficiency of energy
conversion in the vicinity of the ignition threshold for the laser-greenhouse target is investigated in the case of an absorber
having the above properties. Numerical calculations have shown that a thermonuclear-gain coefficient of 1 to 2 (with respect
to the energy absorbed) is attained for a laser-radiation energy of 100 kJ.
Translated from Preprint No. 58 of the P. N. Lebedev Physical Institute, Moscow (1999). 相似文献
13.
M. Nève de Mévergnies 《Applied Physics A: Materials Science & Processing》1981,25(3):275-282
The multiphoton dissociation of CF3Cl induced by TEA-CO2 laser pulses has been studied in a focused beam geometry. TheR(10) [00°1–02°0] (
) laser line was used, so as to dissociate preferentially the minor isotopic component13CF3Cl. The isotopic selectivityS and the dissociation probability per pulse ω were measured in the pressure range between 0.25 and 8 Torr. With short laser
pulses (90 ns FWHM),S is found to increase slightly with gas pressure up to 2 Torr, and ω, to increase almost linearly over the whole pressure
range studied. A schematic model is proposed which satisfactorily explains these results if the transition rates across the
energy level spectrum of the CF3Cl molecules are assumed to increase with gas pressure. 相似文献
14.
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
15.
V. M. Gordienko I. A. Makarov V. P. Petukhov A. S. Khomenko 《Journal of Surface Investigation: X-ray, Synchrotron and Neutron Techniques》2010,4(2):183-188
The dependence of the characteristic X-ray radiation yield from CaF2 crystal on the formed microchannel depth under highly intensive (I ∼ 3 × 1015 W/cm2) laser pulses with different contrast was obtained. The maximum of the characteristic X-ray radiation yield at these experimental
conditions corresponded to the microchannel depth of 30–50 μm. The efficiency of the laser radiation conversion to the characteristic
X-ray radiation increased from 6 × 10−8 for the surface up to 10−7 in the microchannel. The dependence of the characteristic X-ray radiation yield on the viewing angle showed that the source
of X-ray radiation was located near the surface inside the microchannel. 相似文献
16.
An analytical model of K
α radiation of thin laser targets has been developed. It has been shown that, for such targets, the motion of fast electrons
is significant not only in the target itself but also in vacuum. The considered dependences for the free path length of a
fast electron and for the absorption coefficient of laser radiation on the laser intensity with allowance for the electron
motion in vacuum make it possible to match the results of the proposed model with the experimental data on generation of K
α radiation in wide ranges of laser intensities (1018–1021 W/cm2) and thicknesses (1–100 μm) of targets. 相似文献
17.
S.?Firmino?Mendes C.?M.?Costa V.?Sencadas J.?Serrado?Nunes P.?Costa R.?GregorioJr. S.?Lanceros-Méndez 《Applied Physics A: Materials Science & Processing》2009,94(4):899-904
Laser-induced backside wet and dry etching (LIBWE and LIBDE) methods were developed for micromachining of transparent materials.
Comparison of these techniques is helpful in understanding the etching mechanism but was not realized due to complications
in setting up comparable experimental conditions. In our comparative investigations we used a solid tin film for dry and molten
tin droplets for wet etching of fused-silica plates. A tin–fused-silica interface was irradiated through the sample by a KrF
excimer laser beam (λ=248 nm, FWHM=25 ns); the fluence was varied between 400 and 2100 mJ/cm2. A significant difference between the etch depths of the two investigated methods was not found. The slopes of the lines
fitted to the measured data (slLIBDE=0.111 nm/mJ cm−2, slLIBDE=0.127 nm/mJ cm−2) were almost similar. Etching thresholds for LIBDE and LIBWE were approximately 650 and 520 mJ/cm2, respectively. To compare the dependence of etch rates on the pulse number, target areas were irradiated at different laser
fluences and pulse numbers. With increasing pulse number a linear rise of depth was found for wet etching while for dry etching
the etch depth increase was nonlinear. Secondary ion mass spectroscopic investigations proved that this can be due to the
reconstruction of a new thinner tin-containing surface layer after the first pulse. 相似文献
18.
A. A. Serafetinides H. Gonis M. Makropoulou E. Agapitos N. Kavantzas C. Politopoulos D. Yova 《Il Nuovo Cimento D》1995,17(3):213-219
Summary One of the prerequisites for successful laser angioplasty is the ablation of the atherosclerotic lesions, without thermal
or shock-wave damage of the healthy tissue. In this study was evaluated the effectiveness of a TEA CO2 laser, emitting pulses of the lower TEM mode, 100 ns duration, at a repetition rate of 2.4 Hz, for the ablation of cardiovascular
tissue. Normal and atherosclerotic human arteries (post mortem) were irradiated for a range of fluences up to 10J pulse−1 cm−2. After irradiation, the samples were prepared for histologic examination. The results showed that controlled ablation of
normal and atherosclerotic coronary artery can be accomplished with the TEA CO2 laser, with minimal thermal damage. 相似文献
19.
H. J. Ravindra K. Chandrashekaran W. T. A. Harrison S. M. Dharmaprakash 《Applied physics. B, Lasers and optics》2009,94(3):503-511
Single crystals of a chalcone co-crystal (C18H19NO4/C17H16NO3Br; 0.972/0.028) have been grown by slow evaporation from solution. The powder second harmonic generation (SHG) efficiency
of this chalcone co-crystal is 7 times that of urea. The dependence of second harmonic (SH) intensity on particle size revealed
the existence of phase matching direction in this crystal. The large SHG efficiency observed is mainly due to the unidirectional
alignment of molecular dipoles, in which the dipole moment of each molecule adds to establish a net polarization. The weak
N–H⋅⋅⋅O hydrogen-bond interactions help to stabilize the noncentrosymmetric crystal packing and also contribute partly to the SHG.
The better thermal stability, transparency and high laser damage resistance (>1.5 GW cm−2 at 532 nm, 8 ns) of this chalcone co-crystal indicate that it is a promising material for frequency doubling of diode lasers
down to 470 nm. This molecule also shows a third-order NLO response and good optical limiting property of 8 ns laser pulses
at 532 nm. The mechanism for optical limiting in this chalcone was attributed to two-photon induced excited state absorption
that leads to reverse saturable absorption. The structure–property relationship in this chalcone and related compounds is
discussed based on the experimental results and semiempherical hyperpolarizability calculations. 相似文献
20.
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