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1.
Parametric study of optical emission from two successive laser pulses produced chromium and magnesium plasma is presented.
The line emission from chromium and magnesium plasma showed an increase by more than six times for double laser pulse excitation
than for single-pulse excitation. An optimum increase in emission intensity was noted for inter-pulse delay of ∼2–3 μs for
all the elements. The experimental observations were qualitatively explained on the basis of absorption of second laser pulse
in the pre-formed (by first laser) coronal plasma by inverse Bremsstrahlung process, which were found responsible for the
excitation of more ions and atoms in the plasma. This process starts as the plasma scale length becomes greater than the laser
wavelength. This study further indicated the suitability of this technique in the field of elemental analysis 相似文献
2.
In order to analyze the emission spectrum of a laser-induced plasma for obtaining quantitative information on the abundance of the species present in the plasma it is necessary to study the local thermodynamic equilibrium (LTE) conditions in the plasma and determine the best conditions at which they are satisfied. In the present work Nd:YAG laser light pulses (λ=?1064 nm, 6 ns) of different energies (25, 50, 75 and 100 mJ) are focused using a quartz lens (focal length 10 cm) onto certified aluminum alloy samples in air under atmospheric pressure. The emitted spectra are collected and analyzed using an echelle spectrometer coupled with an intensified charge coupled device camera. The temporal history of the plasma is obtained by recording the emission features at predetermined delays and at a fixed gate width (2500 ns). For each spectrum both electron density and excitation temperature are calculated for each delay time and laser pulse energy; we found that the values of the electron density are decreasing from 1018 to 1017 cm-3. The corresponding excitation temperatures were between 30000 and 4000 K depending on the laser pulse energy and the sample used. The LTE conditions were followed up for the different delays and different energies to determine the temporal range in which they are satisfied. It has been found that in the cases of 25- and 50-mJ laser energies, the LTE conditions were satisfied in the chosen delay range (500–5000 ns). On the other hand, for higher laser energies, the LTE conditions were critical at delay times less than 1500 ns and are satisfied for longer delays. 相似文献
3.
H. B. Fu C. S. Chen B. Y. Man X. Song D. Liu 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2011,65(3):509-513
Characteristics of laser produced Pb plasma were investigated using the spectrograph and
the fast photography by an intensified charge coupled device (ICCD) camera. The optical
emission spectra and images of the plasma were recorded and analyzed. The clear
self-reversed structure can be revealed in the emission spectra of the lead plasma when
the target is at 6 mm before the focus of lens. However, the self- absorption can not be
observed in the spectra if the target is located at the focus. The electron temperature,
the electron number density and the lower level atomic number density were obtained by
fitting the experimental spectra at different delay times under the two circumstances. The
electron number density and the lower level atomic number density are higher, as the
target is at 6 mm before the focus of lens, however the electron temperature is lower as
the target is located at the focus, under the same laser energy. 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.
M. Novotný J. Bulíř J. Lančok M. Jelínek Z. Zelinger 《Czechoslovak Journal of Physics》2006,56(4):381-388
Time- and spatially-resolved optical emission spectroscopy was performed to characterize the plasma produced in a hybrid magnetron-sputtering-laser
deposition system, which is used for TiC or SiC thin films preparation. A graphite target was ablated by a KrF excimer laser
(λ=248 nm,τ=20 ns) and either Ti or Si targets were used for DC magnetron sputtering in argon ambient. Spectra were measured in the range
250–850 nm. The evolution of the spectra with varying magnetron powers (0–100 W) and argon pressures (0.3–10 Pa) was studied.
Spectra of the plasmas produced by a) the magnetron alone, b) the ablation laser alone, and c) the magnetron and the ablation
laser together, were recorded. Spectra (a) were dominated by Ar atoms and Ar+ ions. Emission lines of Ti and Si were detected, when Ti target and Si target was used, respectively. Spectra (b) revealed
emission of C, C+, C2, Ar, Ar+. Spectra (c) showed presence of all previously mentioned species and further of Ti+ ions emission was detected.
The research was supported by Grant Agency of the Czech Republic No. 202/06/02161, GA ASCR project number A1010110/01 and
Institutional Research Plan AV CR No. AV0Z 10100522. 相似文献
6.
N. Vogel 《JETP Letters》1998,67(9):647-654
The dynamics of x-ray emission from a low-voltage laser-induced discharge was studied with the aid of a picosecond x-ray streak
camera. Directed x-ray emission in the spectral range from 100 eV to 10 keV in the form of point sources and thin layers with
lifetimes ranging from 30 ps to 1 ns was observed in a low-voltage vacuum discharge (U=150 V) initiated by a picosecond laser beam. X-ray emission from a discharge was detected with a time delay (1–20 ns) relative
to ignition by the laser beam in order to prevent the radiation of the laser plasma from entering the detector. Detection
of directed x-ray emission in a low-voltage vacuum discharge is demonstrated.
Pis’ma Zh. éksp. Teor. Fiz. 67, No. 9, 622–627 (10 May 1998) 相似文献
7.
A. Alonso-Medina 《Journal of Quantitative Spectroscopy & Radiative Transfer》2010,111(14):2043-2051
Transition probabilities for 30 spectral lines, arising from the 5d10 6s{8s, 7p, 5f, 5g} electronic configurations of Pb III (20 measured for the first time), have been experimentally determined from measurements of emission line intensities in a plasma lead induced by ablation with a Nd:YAG laser. The line intensities were obtained with the target placed in molecular argon at 6 Torr, recorded at a 400 ns delay from the laser pulse, which provides appropriate measurement conditions, and analysed between 200 and 700 nm. They are measured when the plasma reaches local thermodynamic equilibrium (LTE). The plasma under study had an electron temperature (T) of 21,400 K and an electron number density (Ne) of 7×1016 cm−3. The influence of self-absorption has been estimated for every line, and plasma homogeneity has been checked. The values obtained were compared with previous experimental values and theoretical estimates where possible. 相似文献
8.
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
9.
激光诱导Cu等离子体特性研究 总被引:1,自引:0,他引:1
实验在大气环境下测定激光诱导Cu等离子体的时间分辨发射光谱,通过对ICCD门宽、ICCD与激光脉冲延迟、增益、激光能量等参数的调节来达到最佳的时间分辨光谱.利用最佳光谱图,通过测定的光谱强度和Stark展宽计算激光诱导Cu等离子体的电子温度和电子密度,得出激光诱导Cu等离子体的电子温度和电子密度时间演化特性.结果表明在本实验条件下延时100-1000 ns范围内变化时,相应的电子温度范围为15000 K-5000 K,在200 ns-500 ns时下降的很快,在500 ns后电子温度下降的越来越平稳;延时在200-900 ns之间变化,等离子体的电子密度一直在下降,延时200-600 ns下降着延时的增加的平缓,600-900 ns下降的很快,随着时间的演化,电子密度也越来越小. 相似文献
10.
11.
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
12.
Comparison between single- and double-pulse LIBS at different air pressures on silicon target 总被引:1,自引:0,他引:1
K. Amal S.H. Elnaby V. Palleschi A. Salvetti M.A. Harith 《Applied physics. B, Lasers and optics》2006,83(4):651-657
A comparative study between single- and double-pulse laser-induced breakdown spectroscopy (LIBS) was performed on an n-type silicon(111) target. A new mobile double-pulse instrument for LIBS analysis was used for the measurements. The experiment was carried out at different air pressures of 0.7, 470 and 1000 hPa. It has been found that, in the case of double-pulse LIBS, the emission intensities of atomic and ionic lines are strongly enhanced at higher pressures. Using Stark broadening of the atomic lines of silicon, it was found that the electron number densities for single and double pulses are approximately the same (Ne∼1017 cm-3). Plasma excitation and ionization temperatures were determined from a Boltzmann plot. The double-pulse laser-induced plasma was studied at different interpulse delay times of 1, 2, 5, 10, 15, 25 and 50 μs. The results indicated that the interaction between the laser, plasma and target gives higher atomic and ionic intensities at shorter interpulse delay times. PACS 52.38.Mf; 79.20.Ds; 52.50.Jm 相似文献
13.
V. K. Unnikrishnan Kamlesh Alti V. B. Kartha C. Santhosh G. P. Gupta B. M. Suri 《Pramana》2010,74(6):983-993
Plasma produced by a 355 nm pulsed Nd:YAG laser with a pulse duration of 6 ns focussed onto a copper solid sample in air at
atmospheric pressure is studied spectroscopically. The temperature and electron density characterizing the plasma are measured
by time-resolved spectroscopy of neutral atom and ion line emissions in the time window of 300–2000 ns. An echelle spectrograph
coupled with a gated intensified charge coupled detector is used to record the plasma emissions. The temperature is obtained
using the Boltzmann plot method and the electron density is determined using the Saha-Boltzmann equation method. Both parameters
are studied as a function of delay time with respect to the onset of the laser pulse. The results are discussed. The time
window where the plasma is optically thin and is also in local thermodynamic equilibrium (LTE), necessary for the laser-induced
breakdown spectroscopy (LIBS) analysis of samples, is deduced from the temporal evolution of the intensity ratio of two Cu
I lines. It is found to be 700–1000 ns. 相似文献
14.
The laser produced plasma in air by Q-switch Nd:YAG pulses with 50 mJ and 7 ns was analyzed using Mach-Zehnder interferometer. The interferograms were taken at various delay times after single pulses induced gas breakdown. The 3D electron density distribution at early times of the plasma is investigated. To determine the 3D electron density distribution of the plasma, the FFT analysis is applied to extract the phase of the reconstructed interferograms and the numerical inverse Abel transformation is used to calculate the refractive index. The results provide an understanding of the electron density temporal and spatial evolution of laser induced plasma in air from 18 ns and up to 100 ns of plasma lifetime. 相似文献
15.
Enrique Camps L. Escobar-Alarcón V. H. Castrejón-Sánchez P. Tolentino-Eslava 《Applied Physics A: Materials Science & Processing》2008,93(3):759-763
Amorphous carbon thin films were deposited by laser ablation of a graphite target, using the fundamental line of a 5 ns Nd:YAG
laser. Deposition was carried out as a function of the plasma parameters (mean kinetic ion energy and plasma density), determined
by means of a planar probe. In the selected working regimes the optical emission from the plasma is mainly due to atomic species,
namely C+ (426.5 nm); however, there is also emission from other atomic species and molecular carbon. The hardness and resistivity
could be varied in the range between 10 and 25 GPa, and 108 and 1011 Ω cm, respectively. The maximum values were obtained at a 200 eV ion energy and 6×1013 cm−3 plasma density, where the maximum quantity of C–C sp3 bonds was formed, as confirmed by Raman spectroscopy. 相似文献
16.
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
17.
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
18.
利用波长532nm,脉宽15ns的Nd:YAG 激光器作用于Cu靶上,研究了产生等离子体的紫外段(180 nm~300 nm)发射光谱。在局部热力学平衡条件下,采用Boltzmann图表法估算了等离子体的电子温度,得到了电子温度随时间和空间的变化,以及电子温度随激光能量密度的变化。结果显示,随着激光能量的变化,电子温度有一个极大值。随着时间的发展,电子温度先减小,而后增大,接着缓慢减小。随着距靶面距离的增加,电子温度呈下降趋势。 相似文献
19.
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
20.
利用Nd:YAG激光器产生的1064 nm、10 ns脉冲激光聚焦在空气中的Ti靶,观测了激光诱导Ti等离子体发射光谱.调节激光能量为45 mJ/pulse,分析了时间范围在0到4000 ns的时间分辨发射光谱和谱线轮廓以及展宽.在局部热力学平衡(LTE)条件下,利用Saha-boltzmann图法拟合电子温度,Saha方程计算电子密度,讨论了等离子体电子温度和电子密度随时间的演化规律.结果表明,在所讨论的时间范围内,谱线的强度在延时250 ns处达到最大,250 ns后随着延迟时间的增加减小,电子密度和电子温度在延时1000 ns内快速衰减,1000 ns后衰减速度变慢. 相似文献