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Measurements of multiphoton ionization coefficients with ultrashort ultraviolet laser pulses 总被引:1,自引:0,他引:1
Multiphoton ionization coefficients of atmospheric gases were measured with ultrashort ultraviolet laser pulses. The values
were obtained using two different experimental setups and the pressure range covered four orders of magnitude. The coefficients
were pressure-independent and consistent with numbers predicted by the nonresonant Keldysh theory.
Received: 13 June 2000 / Revised version: 5 October 2000 / Published online: 7 February 2001 相似文献
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The analytic formula of the ionization efficiency in the process of double resonance enhanced multi-photon ionization (DREMPI) is derived from the dynamic rate equation about the interaction of photon and material. Based on this formula, the ionization efficiency and the laser power index versus laser intensity in the DREMPI process of NO molecule, via A2E and S2E intermediate resonant states, is numerically simulated. It is shown that the ionization efficiency of NO molecule increases with the laser intensity until getting saturation, while the laser power index decreases with the enhancement of the laser intensity and changes to zero at last. The variation of the laser power index with the laser intensity indicates that the ionization efficiency reaches saturation in the one, two, and three excitation steps respectively. It is also found that the narrower the laser pulse duration is, the higher becomes the laser intensity for saturation. 相似文献
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Effects of the carrier-envelope phase of chirped laser pulses in the multiphoton ionization regime 总被引:1,自引:0,他引:1
By solving the time-dependent Schr?dinger equation for the Cs atom, we find that, as long as the spectral bandwidth is sufficiently broad, the asymmetry of photoelectron ejection is strongly phase dependent and persists even when the chirped pulse duration becomes more than several cycles. The asymmetry survives even after the angle integration over the hemisphere, implying that the detection efficiency can be significantly improved. This counterintuitive and robust finding provides a simple way to measure the phase for both transform-limited and chirped pulses. 相似文献
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A classical ensemble method is used to investigate nonsequential double ionization(NSDI) of Ar atoms irradiated by linearly polarized few-cycle laser pulses. The correlated-electron momentum distribution(CMD) exhibits a strong dependence on the carrier-envelope phase(CEP). When the pulse duration is four cycles, the CMD shows a cross-like structure, which is consistent with experimental results. The CEP dependence is more notable when the laser pulse duration is decreased to two cycles and a special L-shaped structure appears in CMD. Recollision time of returning electrons greatly depends on CEP, which plays a significant role in accounting for the appearance of this structure. 相似文献
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Eremina E Liu X Rottke H Sandner W Schätzel MG Dreischuh A Paulus GG Walther H Moshammer R Ullrich J 《Physical review letters》2004,92(17):173001
The electron momentum correlation after nonsequential double ionization of N2 and O2 in ultrashort light pulses at light intensities near 1.5 x 10(14) W/cm(2) has been investigated. The experimental results reveal distinctive differences between the molecular species and between molecules and atoms of similar ionization threshold. We provide evidence that recollision double ionization is the essential mechanism and trace the origin of the differences back to the symmetry of the orbitals occupied by the valence electrons. 相似文献
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We report for the first time the proper conditions to observe Autler-Townes splitting (ac-Stark splitting) from vibrationally coherent states belonging to the different electronic terms of a diatomic molecule. Wave packet dynamics simulations demonstrate that such a process is feasible by multiphoton resonance ionization of the molecule Na2 with a single ultrashort intense laser pulse. With the ultrahigh time resolution of a femtosecond laser pulse, one can directly measure the absolute value of the transition dipole moment between any kinds of molecular states by this kind of Autler-Townes splitting, which is a function of the internuclear distance R. 相似文献
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E. A. Volkova V. V. Gridchin A. M. Popov O. V. Tikhonova 《Journal of Experimental and Theoretical Physics》2006,102(1):40-52
The ionization of a hydrogen atom in a linearly polarized low-frequency electromagnetic field is investigated by direct numerical integration of the time-dependent Schrödinger equation. The data obtained for various ionization regimes and various initial atomic states are compared with the Keldysh and Perelomov-Popov-Terent’ev (PPT) theories. The validity ranges for the quasi-static model of tunneling ionization and the PPT theory in laser intensity and frequency are determined. The tunneling ionization of the excited 2s and 2p states is discussed. The ionization of a hydrogen atom in an ultrashort (on the order of one optical period) pulse is investigated. 相似文献
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We investigate differential electron momentum distributions in nonsequential double ionization with linearly polarized, few-cycle pulses, using a classical model based on a laser-assisted inelastic (e(-),2e(-)) rescattering mechanism. These yields, as functions of the momentum components parallel to the laser polarization, are highly asymmetric and strongly influenced by the phase difference between the pulse envelope and its carrier oscillation, radically changing their sign around a critical phase. This behavior provides a powerful tool for absolute-phase measurements. 相似文献
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R. Le Harzic D. Breitling S. Sommer C. Föhl K. König F. Dausinger E. Audouard 《Applied Physics A: Materials Science & Processing》2005,81(6):1121-1125
Experimental results related to the influence of time delayed pulses for ablation efficiency with short multi pulses (pulse duration of 5 ps) are reported. A significant improvement of the micro structuring quality at relatively high fluence regime in metals is obtained. Less removed or recast matter is observed and the processed surface appears to be smoother with better roughness. Ablation depths and burr heights are compared for single pulses and double pulses in steel, Al and Cu as a function of scans number. Best results are obtained for weak time delays, typically less than 1 ps. PACS 79.20.Ds; 42.62.Cf; 81.65.Cf 相似文献
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We explore the excitation of water molecules subject to short and intense laser pulses in the frame of time-dependent density function theory (TDDFT) at the level of the time-dependent local-density approximation (TDLDA), applied to valence electrons, coupled non-adiabatically to molecular dynamics (MD) of ions. We first study the optical absorption spectra of the water molecule as an observable in the "linear" domain and results are in good agreement with experiments. We then explore the influence of the laser frequency on the excitation. It is found that when the laser frequency is off-resonant or highly above the resonant region, the excitations are weak whereas for the resonant frequency case, the ionization is enhanced and bond lengths are enlarged. Furthermore, a direct coupling of ions with the laser pulse with the off-resonant frequency is found when investigating the OH bond lengths. We finally study the effect of laser intensity on the excitation of H 2 O and it is found that ionization increases when the laser intensity varies from low to high and we observe stable vibrations to Coulomb fragmentation when the ionization is up to typically two more charge units. 相似文献
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本文利用三维经典系综模型研究了低强度周期量级脉冲驱动排列分子的非次序双电离. 结果表明, 电子对的关联特性强烈地依赖于分子的排列方向和激光脉冲的载波包络相位; 垂直分子反关联电子对的比例总是高于平行分子反关联电子对的比例; 当载波包络相位从0到π 逐渐增加时, 反关联电子对的数目先增加再减少; 对于平行分子, 电子对的释放总是以正关联为主; 而垂直分子的主导关联模式则依赖于激光脉冲的载波包络相位, 当载波包络相位为0.3π-0.7π之间时, 电子对以反关联释放为主, 其他相位下以正关联为主. 本文利用分子势能曲线和电子返回能量很好地解释了电子关联特性对分子排列方向和载波包络相位的依赖关系. 相似文献
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Competition between multiphoton/tunnel ionization and filamentation induced by powerful femtosecond laser pulses in air 总被引:1,自引:0,他引:1
In this work we present experiments by focusing 42 femtosecond laser pulses in air using three differentfocal length lenses: f=100, 30 and 5 cm. For the longest focal length, only the filament, which is aweak plasma column,is observed. When the shorter focal length lens is used, a high density plasma isgenerated near the geometrical focus and coexists with a weak plasma channel of the filamemt. Under thetightest focusing condition, filamentation is prevented and only a strong plasma volume appears at tehgeometrical focus. 相似文献