共查询到20条相似文献,搜索用时 62 毫秒
1.
IJ. Kim I. W. Choi S. K. Lee K. A. Janulewicz J. H. Sung T. J. Yu H. T. Kim H. Yun T. M. Jeong J. Lee 《Applied physics. B, Lasers and optics》2011,104(1):81-86
An ultrahigh contrast laser pulse of over 1011 for 6 ps before the main pulse was achieved by employing a double plasma mirror installed at the end of a 100 TW Ti:sapphire
laser system. Spatial beam qualities such as focusability and stability were found to be extremely sensitive in the range
of 14–360 J/cm2 on the double plasma mirror, while ultrahigh contrast was maintained. At the fluence of 90 J/cm2 the focusability of the ultrahigh contrast laser was not degraded, and the stability was very close to that obtained without
the double plasma mirror when the 2-dimensional normalized standard deviation and the correlation function for several laser
beam profiles were analyzed. These results are requisites for carrying out relativistic laser-plasma interactions with ultrahigh
contrast laser pulses, enabling the use of ultrathin solid targets. 相似文献
2.
We report here an experimental study of the ionic keV X-ray line emission from magnesium plasma produced by laser pulses of
three widely different pulse durations (FWHM) of 45 fs, 25 ps and 3 ns, at a constant laser fluence of ∼1.5 × 104 J cm − 2. It is observed that the X-ray yield of the resonance lines from the higher ionization states such as H- and He-like ions
decreases on decreasing the laser pulse duration, even though the peak laser intensities of 3.5 × 1017 W cm − 2 for the 45 fs pulses and 6.2 × 1014 W cm − 2 for the 25 ps pulses are much higher than 5 × 1012 W cm − 2 for the 3 ns laser pulse. The results were explained in terms of the ionization equilibrium time for different ionization
states in the heated plasma. The study can be useful to make optimum choice of the laser pulse duration to produce short pulse
intense X-ray line emission from the plasma and to get the knowledge of the degree of ionization in the plasma. 相似文献
3.
Hideyuki Horisawa Shigeru Yamaguchi Ikkoh Funaki 《Applied Physics A: Materials Science & Processing》2011,104(3):935-940
Fundamental investigations of plasma diagnostics of a forward laser plasma acceleration employing laser–foil interactions
were conducted for an Al-foil target irradiated with an Nd:YAG laser of 1 J/pulse with pulse width of 10 ns. Temporal evolutions
of electron temperatures and densities were evaluated with electrostatic probes and spectroscopic diagnostics. From the results,
it was shown that an average speed of ions in a forward direction was about 40 km/s. Also, it was shown that the plasma temperature
and density were about 2.5–8 eV and 1010 cm−3, respectively. 相似文献
4.
D. Puerto W. Gawelda J. Siegel J. Bonse G. Bachelier J. Solis 《Applied Physics A: Materials Science & Processing》2008,92(4):803-808
We have studied the plasma formation and ablation dynamics in fused silica upon irradiation with a single 120 fs laser pulse
at 800 nm by using fs-resolved pump-probe microscope. It allows recording images of the laser-excited surface at different
time delays after the arrival of the pump pulse. This way, we can extract both the temporal evolution of the surface reflectivity
and transmission, at 400 nm, for different spatial positions in the spots (and thus for different local fluences) from single
series of images. At fluences well above the visible ablation threshold, a fast and large increase of the reflectivity is
induced by the formation of a dense free-electron plasma. The maximum reflectivity value is reached within ≈1.5 ps, while
the normalized transmission decreases within ≈400 fs. The subsequent temporal evolution of both transient reflectivity and
transmission are consistent with the occurrence of surface ablation. In addition, the time-resolved images reveal the existence
of a free-electron plasma distribution surrounding the visible ablation crater and thus formed at local fluences below the
ablation threshold. The lifetime of this sub-ablation plasma is ≈50 ps, and its maximum electron density amounts to 5.5×1022 cm−3. 相似文献
5.
S. Fourmaux C. Serbanescu R. E. Kincaid A. Krol J. C. Kieffer 《Applied physics. B, Lasers and optics》2009,94(4):569-575
We report K
α
x-ray production with a high energy (110 mJ per pulse at 800 nm before compression/15 mJ at 400 nm after compression), high
repetition rate (100 Hz), and high pulse contrast (better than 10−9 at 400 nm) laser system. To develop laser-based x-ray sources for biomedical imaging requires to use high-energy and high-power
ultrafast laser system where compression is achieved under vacuum. Using this type of laser system, we demonstrate long-term
stability of the x-ray yield, conversion efficiency higher than 1.5×10−5 with a Mo target, and the x-ray spot size close to the optical focal spot. This high-repetition K
α
x-ray source can be very useful for x-ray phase-contrast imaging.
S. Fourmaux and C. Serbanescu contributed equally to this work. 相似文献
6.
The generation of lower (third) and higher harmonics of femtosecond laser radiation in plasmas produced by laser ablation
of different targets with a small atomic number Z (B, Be, Li) has been investigated. The high (10−3) efficiency of third-harmonic generation was observed in plasma produced on the boron surface. Efficient third-harmonic generation
was also observed in beryllium plasma using femtosecond pulses of Ti:sapphire laser radiation (λ = 790 nm) and its second
harmonic (395 nm). We could tune the higher harmonics generation spectrum by tuning the crystal converter when using 395-nm
radiation to be converted. It is shown that, in plasmas formed on targets with small Z, the conversion efficiency and limiting generated harmonic order depend on the delay between the ablation pulse and the pulse
to be converted. 相似文献
7.
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
8.
Material ablation and plasma plume expansion study from Fe and graphite targets in Ar gas atmosphere
S. Mahmood R. S. Rawat S. V. Springham T. L. Tan P. Lee 《Applied Physics A: Materials Science & Processing》2010,101(4):695-699
Study of expansion dynamics of pulsed-laser ablation plasmas from Fe and graphite targets is presented. A 532 nm Q-switched
Nd:YAG laser with fluence of 30 J cm−2 is used to ablate the Fe and graphite targets in various Ar ambient gas pressures. Plasma ablation parameters for the two
target materials are estimated using snow-plow and shock-wave models, which show that the laser beam energy deposited to ablated
species remains at 70% for both targets at all ambient pressures. The plume splitting was observed, more prominently, for
Fe plasma as it moves faster compared to graphite plasma. The difference in plasma plume fronts’ speeds for different targets
was attributed to the significant difference in mass of the ablated plasma for two targets, as estimated from simulation results. 相似文献
9.
A new scheme is proposed for proton and light-ion acceleration to relativistic energies by superstrong laser radiation interacting
with a structured plasma target. The proposal consists in the use of two-component targets consisting of heavy and light ions,
where an ambipolar field is formed under the action of the ponderomotive force of incident radiation, and, in contrast to
the traditional schemes, acceleration starts from the front boundary of the layer. It is shown that, for the optimized target
parameters, monoenergetic GeV ion beams can be produced for radiation pulse intensities on the order of 1021−1022 W/cm2. 相似文献
10.
We report on the implementation of intensity-dependent filter for picosecond pulse temporal cleaning based on an effect of
pulse polarization rotation during the unbalanced phase matched second harmonic generation. The pulse contrast enhancement
by more than two orders of magnitude and filter transmission of ∼25% has been demonstrated at pulse intensities of <1 GW/cm2. A simple and reliable all-solid-state filter scheme was integrated in a two-stage picosecond Nd:YAG regenerative amplifier
seeded with pJ-energy femtosecond pulses of the Yb:KGW oscillator, and allowed us to reduce the ASE intensity level down to
1.5×10−8 with reference to the intensity of main 100 ps and 100 μJ pulse. 相似文献
11.
A high power pulse Nd-glass laser system with plasma mirror is studied. Plasma is created on the surface of a solid target and the action is superradiantly triggered. Long trains of modelocked pulses are generated if the carbon or metal targets are used and Q-switched pulses are observed with dielectric targets like PVC. Tens of joules of light energy are extracted from the laser medium and absorbed by plasma in both regimes. Spatial and temporal structures of the laser beam are very reproducible, the laser action is insensitive to variations in air pressure inside the target chamber. Stimulated Brillouin back-scattering in the underdense plasma is discussed as the nonlinear mechanism governing the plasma reflectivity. 相似文献
12.
A sequential three-dimensional (3D) particle-in-cell simulation code PICPSI-3D with a user friendly graphical user interface
(GUI) has been developed and used to study the interaction of plasma with ultrahigh intensity laser radiation. A case study
of laser–plasma-based electron acceleration has been carried out to assess the performance of this code. Simulations have
been performed for a Gaussian laser beam of peak intensity 5 × 1019 W/cm2 propagating through an underdense plasma of uniform density 1 × 1019 cm − 3, and for a Gaussian laser beam of peak intensity 1.5 × 1019 W/cm2 propagating through an underdense plasma of uniform density 3.5 × 1019 cm − 3. The electron energy spectrum has been evaluated at different time-steps during the propagation of the laser beam. When the
plasma density is 1 × 1019 cm − 3, simulations show that the electron energy spectrum forms a monoenergetic peak at ~14 MeV, with an energy spread of ±7 MeV.
On the other hand, when the plasma density is 3.5 × 1019 cm − 3, simulations show that the electron energy spectrum forms a monoenergetic peak at ~23 MeV, with an energy spread of ±7.5 MeV. 相似文献
13.
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
14.
S.?Sujecki L.?Sójka E.?Bere?-Pawlik Z.?Tang D.?Furniss A.?B.?Seddon T.?M.?Benson 《Optical and Quantum Electronics》2010,42(2):69-79
A simple Dy3+-doped chalcogenide glass fibre laser design for mid-infrared light generation is studied using a one dimensional rate equation
model. The fibre laser design employs the concept of cascade lasing. The results obtained demonstrate that efficient cascade
lasing may be achieved in practice without the need for fibre grating fabrication, as a sufficient level of feedback for laser
action is provided by Fresnel light reflection at chalcogenide glass fibre–air interfaces. Further enhancement of the laser
efficiency can be achieved by terminating one of the fibre ends with a mirror. A numerical analysis of the effect of the Dy3+ doping concentration and fibre loss on the laser operation shows that with 5 W of pump power, at 1.71 μm wavelength, output
powers above 100 mW at ∼ 4.5 μm wavelength can be achieved with Dy3+ ion concentrations as low as 3 × 1019 cm−3, when fibre loss is of the order 1dB/m. 相似文献
15.
R. A. Ganeev H. Singhal P. A. Naik J. A. Chakera A. K. Srivastava T. S. Dhami M. P. Joshi P. D. Gupta 《Applied physics. B, Lasers and optics》2010,100(3):581-585
The results of enhanced harmonic generation in fullerene-containing plasma plumes using laser radiation of different wavelengths,
pulse durations, and phase modulation are presented. Odd and even harmonics up to the 29th order of 800 nm radiation have been extended in the case of two-color orthogonal polarization pump of C60-containing plasma plumes. The conversion efficiency for the odd and even harmonics in the vicinity of SPR of the C60-containing plasma (40–70 nm) was estimated to be in the range of 10−4. 相似文献
16.
N. Muhammad D. Whitehead A. Boor W. Oppenlander Z. Liu L. Li 《Applied Physics A: Materials Science & Processing》2012,106(3):607-617
The demand for micromachining of coronary stents by means of industrial lasers rises quickly for treating coronary artery
diseases, which cause more than one million deaths each year. The most widely used types of laser for stent manufacturing
are Nd:YAG laser systems with a wavelength of 1064 nm with pulse lengths of 10−3–10−2 seconds. Considerable post-processing is required to remove heat-affected zones (HAZ), and to improve surface finishes and
geometry. Using a third harmonic laser radiation of picosecond laser (6×10−12 s pulse duration) in UV range, the capability of the picosecond laser micromachining of nitinol and platinum–iridium alloy
for coronary stent applications are presented. In this study dross-free cut of nitinol and platinum–iridium alloy tubes are
demonstrated and topography analysis of the cut surface is carried out. The HAZ characteristics have been investigated by
means of microscopic examinations and measurement of micro-hardness distribution near the cut zones. 相似文献
17.
We show that photoionization of wide band gap silicate glasses by infrared ultrashort laser pulses can occur without laser-induced
damage. Two glasses are studied, fused silica and a multi-component silicate photo-thermo-refractive (PTR) glass. Experiments
are performed by low numerical aperture focusing of ultrashort laser pulses (100 fsec<τ<1.5 psec) at the wavelengths 780 nm, 1430 nm, and 1550 nm. Filaments form inside both glasses and are visibly observable
due to intrinsic luminescence. Keldysh’s theory of nonlinear photoionization is used to model the formation of filaments and
values of about 1013 W cm−2 for the laser intensity and 1019 cm−3 for the free electron density are estimated for stable filaments to arise. Laser-induced damage is studied by the generation
of a third harmonic from an interface created between a damage site and the surrounding glass matrix. It is found that third
harmonic generation occurs only after several thousands of laser shots indicating that damage is not a single-shot phenomena.
The ability to photoionize PTR glass without damage by ultrashort laser pulses offers a new approach for fabricating diffractive
optical elements in photosensitive glass. 相似文献
18.
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
19.
The mechanism of generation of terahertz radiation upon irradiation of a target by short (∼ 0.1 ns) high-intensity laser pulses
(I ∼ 1018−1019 W cm−2) is investigated by numerical simulation using the relativistic electromagnetic PIC code. The interaction of such a pulse
with the target, a plasma is formed on it. Electrons emitted from the plasma form a virtual cathode whose oscillations are
determined not only by their self-field, but also by the field of ions of the plasma. Generation occurs in the terahertz frequency
range with the efficiency thrice as high as in the absence of ions (i.e., with traditional reditron generation mechanism).
The explanation for this effect is also given. 相似文献
20.
A new scheme is proposed for proton and light-ion acceleration to relativistic energies by superstrong laser radiation interacting
with a structured plasma target. The proposal consists in the use of two-component targets consisting of heavy and light ions,
where an ambipolar field is formed under the action of the ponderomotive force of incident radiation, and, in contrast to
the traditional schemes, acceleration starts from the front boundary of the layer. It is shown that, for the optimized target
parameters, monoenergetic GeV ion beams can be produced for radiation pulse intensities on the order of 1021−1022 W/cm2.
Original Russian Text ? A.V. Korzhimanov, A.A. Gonoskov, A.V. Kim, A.M. Sergeev, 2007, published in Pis’ma v Zhurnal éksperimental’noĭ
i Teoreticheskoĭ Fiziki, 2007, Vol. 86, No. 9, pp. 662–669. 相似文献