共查询到20条相似文献,搜索用时 15 毫秒
1.
The effects of different laser pulse widths on laser-induced ionization imaging of microstructures embedded in transparent materials are investigated. It is shown that a femtosecond laser-induced ionization probe can detect the variation of elemental composition of the sample materials with a higher contrast ratio, whereas the ionization probe generated by picosecond laser pulses is more sensitive to the structural change inside optical materials, which can be well explained by the different roles of multiphoton ionization and avalanche ionization involved in material breakdown. These results also suggest that an optimum diagnosis could be obtained if well-selected laser parameters are employed in ultrafast laser ionization imaging. 相似文献
2.
Analytic formula of the efficiency of optical-optical double-color double-resonance multi-photon ionization (OODR-MPI) is derived from the dynamic rate equation about the interaction of photon and material. Based on this formula, the influence of characteristic of the pump and probe laser on the ionization efficiency of (1+2+1) OODR-MPI process is simulated theoretically. It is shown that the pump laser will affect the ionization efficiency by the number control of the molecules excited to the first resonance state. The ionization efficiency is decided by the probe laser directly. Both of the excited molecules and ionization efficiency increase with the intensity and pulse duration of the laser until saturation. It is also found that the longer the delay time of the probe laser to the pump one is, the lower the ionization efficiency would be. The delay time ought to be smaller than the lifetime of the excited molecule in the practical use of the OODR-MPI technique. 相似文献
3.
We present a new interferometric setup where interference of a fast probe electron affects the ionization cross section of an atom. Interference is detected in the intensity of the inelastically scattered electrons at the Bragg scattering angle in transmission. The crystal serves both as a target for core ionization and as a beam-splitting and phase-shifting device. 相似文献
4.
Favre M. Choi P. Chuaqui H. Kaufman Y. Moreno J. Wyndham E. Zambra M. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1995,23(3):212-220
A detailed experimental study of space charge formation and ionization growth in transient hollow cathode discharges (THCD) is presented. The experiment was performed with an applied step voltage up to 30 kV, with rise time less than 50 ns. The discharge was operated in different gases, at pressures in the range 50-750 mTorr, with cathode apertures ranging from 1 to 5 mm diameter and 5 to 20 mm long, with 10 cm electrode separation. Spatial charge formation, both in the hollow cathode region (HCR) and inter electrode space, has been studied with a capacitive probe array. Properties of high energy electron beams have been measured with a beam-target scintillator-photomultiplier arrangement. Detailed correlations of the electron beam evolution with the charge probe signals inside and outside the HCR clearly demonstrate the role of the electron beam in the initial formation and late evolution of a virtual anode and, in turn, the field enhanced ionization when the anode potential is brought close to the HCR. These results clearly identify the different regimes in which the Hollow Cathode plays a significant role in ionization growth in the inter electrode space and in the processes which eventually lead to electric breakdown 相似文献
5.
S. Klagge 《等离子体物理论文集》1975,15(6):309-317
On the example of the Ne glow discharge with a benzol admixture the possibility of applicating the probe diagnostic in polymerizing plasmas is investigated. Heating the probe at 900°C stetady values for the floating potential, the probe characteristic and its second derivation are obtained. The variation with time of these quantities without heating the probe yields informations about the rate of polymerization. The effect of a benzol admixture from 1% to 20% on the energy distribution function of electrons and the plasma parameters in the tube axis is pointed out. From the second derivation of the characteristic at emissive probe conditions it is possible to deduce in addition to the space potential the influence of the benzol admixture on the ionization mechanism. 相似文献
6.
Zeidler D Staudte A Bardon AB Villeneuve DM Dörner R Corkum PB 《Physical review letters》2005,95(20):203003
We investigate the dynamics of double ionization in aligned nitrogen molecules. An ultrashort, weak laser pulse creates an aligned ensemble of molecules that is ionized with a subsequent, strong probe pulse. We find that the two electrons involved in nonsequential double ionization more likely exit the molecule in the same direction if it is parallel to the probe laser polarization, indicating that they are ejected within a few hundred attoseconds of each other. Double ionization is less probable and takes longer for perpendicular molecules. 相似文献
7.
Ionization of atoms by the spatial gradient of the pondermotive potential in a focused laser beam is investigated. Rydberg ions, formed during the interaction of noble gas atoms with an intense laser pulse, are used to probe the gradient field. Rydberg ion species with higher ionization potentials are produced at locations where the gradient field is largest. The measured Rydberg ion yields differ dramatically from estimates that ignore gradient-field ionization, but are in good agreement with predictions that include the effect. 相似文献
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10.
J. Glosík 《Czechoslovak Journal of Physics》1977,27(5):550-554
The influence of ionization waves irregularity on electron distribution function (EDF) measurement has been investigated. The probe method with sampling technique has been applied. The results show that the time irregularity of high amplitude ionization waves may cause an error in interpretation of the EDF measurement. 相似文献
11.
Fluctuations of the electric field, the charged particle density, the electron temperature and the plasma potential are simultaneously measured by a probe in the positive column of helium glow discharge at a few torr gas pressure by exciting a small amplitude ionization wave. It is proposed that these values can be determined by analyzing the probe current. 相似文献
12.
Fluctuations of the electric field, the charged particle density; the electron temperature and the plasma potential are simultaneously measured by a probe in the positive column of helium glow discharge at a few torr gas pressure by exciting a small amplitude ionization wave. It is proposed that these values can be determined by analyzing the probe current. 相似文献
13.
We experimentally and numerically investigate the intracavity ionization of a dilute gas target by an ultrashort pulse inside a femtosecond enhancement cavity. Numerical simulations detail how the dynamic ionization of the gas target limits the achievable peak intensity of the evolving intracavity pulse beyond that of linear cavity losses, setting a constraint on the strength of the nonlinear interaction that can be sustained in such optical cavities. Experimental measurements combined with numerical simulations predict ionization levels in a femtosecond enhancement cavity for the first time. We demonstrate how the resonant response of the femtosecond enhancement cavity can itself be used as a sensitive probe of optical nonlinearities at high intensities. 相似文献
14.
A theory is developed for a probe in a strongly ionized high-pressure plasma. The situation discussed is typical of high-pressure
plasmas, where the plasma occupying most of the near-probe layer is in a state of local ionization equilibrium with a common
temperature for electrons and heavy particles. The possibility of determining the parameters of the unperturbed plasma by
analyzing the probe characteristics on its ion saturation segment, transient segment, and for a floating probe potential is
discussed. The calculations are carried out for the example of a strongly ionized xenon plasma at atmospheric pressure.
Zh. Tekh. Fiz. 67, 16–20 (December 1997) 相似文献
15.
《中国物理快报》2016,(4)
We experimentally investigate the double ionization of molecular hydrogen subjected to ultrashort intense laser pulses.The total kinetic energy release of the two coincident H~+ ions,which provides a diagnosis of different processes to double ionization of H_2,is measured for two different pulse durations,i.e.,25 and 5fs,and various laser intensities.It is found that,for the long pulse duration(i.e.,25 fs),the double ionization occurs mainly via two processes,i.e.,the charge resonance enhanced ionization and recollision-induced double ionization.Moreover,the contributions from these two processes can be significantly modulated by changing the laser intensity.In contrast,for a few-cycle pulse of 5fs,only the recollsion-induced double ionization survives,and in particular,this process could be solely induced by the first-return recollision at appropriate laser intensities,providing an efficient way to probe the sub-laser-cycle molecular dynamics. 相似文献
16.
M.H. Elghazaly S. Solyman 《Journal of Quantitative Spectroscopy & Radiative Transfer》2007,103(2):260-271
Some easy to use reasonable approximations for electron impact rate coefficients have been considered. The most important rate coefficients for electron collisions in noble gases are electron-neutral ionization and electron impact excitation. Electron-neutral ionization besides electron impact excitation of some states of the argon and helium atom in direct current (dc) glow discharge plasma has been calculated. The plasma parameters of electron are significant factors for computing the rate coefficients. We present first results of probe diagnostic that includes the double probe measurements of the plasma parameters, namely, electron temperature (Te) and electron density (ne). Electron properties obtained from the double probe characteristic curves including Te and ne as well as the calculated rate coefficients (ionization and excitation) were studied as a function of the axial distance from the cathode while the discharge operating parameters of voltage and pressure were varied. Two regions of the glow discharge were investigated: cathode fall region and negative glow. Particular emphasis was placed on the negative glow region. 相似文献
17.
K. Thomson M. Ziskind C. Mihesan E. Therssen C. Focsa 《Applied Surface Science》2007,253(15):6435-6441
Characterization of polycyclic aromatic hydrocarbons (PAHs) samples has been performed by laser desorption combined with multi-photon ionization technique using two different geometries of the ionization laser beam. This comparative study evidences the strong influence of ionization laser fluence on PAH fragmentation. Through a ∼103 enlargement of the ionization probe volume and 104 reduction of laser fluence over previous studies, fragment free mass spectra are obtained with higher sensitivity and selectivity. The ability to measure fragment free PAH mass spectra is a very important step in the end goal of measuring complex unknown mixtures of PAH desorbed from solid surface such as soot samples. 相似文献
18.
Results of the probe and thermocouple measurements of the constricted stationary glow dis charge in nitrogen and air at pressures up to 60 Torr are given. It was shown that the main energy processes in the column are the heating of the gas and its vibrational excitation. The balance of charged particles is determined by the electron-ion recombination and the stepwise ionization through metastable levels of nitrogen molecules. The results obtained can be used in the numerical simulation of a moving filament during the current constriction in the glow discharge. 相似文献
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