Measurement Of Phase Of Ultrashort Pulses And Electron Correlation In Nonsequential Double Ionization

The key work of this dissertation has systematically studied strong-field ionization, one of the fundamental highly nonlinear optical phenomena in the interaction of matter and intense laser pulses. The content mainly contains the dependence of above-threshold ionization on the carrier-envelope phase of few-cycle pulses and the effect of electron correlation in strong-field nonsequential double ionization, including the dependence on the carrier-envelope phase, manipulating the dynamics in nonsequential double ionization process via the permanent dipole of molecules and the microscopic dynamics in the resonant double ionization at laser intensities below the recollision threshold.For few-cycle pulses, the rescattered photoelectrons in above-threshold ionization are predominantly created in short time intervals near the maximum of the pulse envelope. By quantum mechanical calculations, we find that the large-scale fringes in the high-energy photoelectron energy spectra induced by the interference of the long and short quantum orbits are very sensitive to the carrier-envelope phase of few-cycle pulses, especially at high laser intensities. Therefore, we propose a method to accurately measure the carrier-envelope phase. Measuring the slight shift of the interference fringes in the high-energy cutoff region can achieve the precise measurement of the carrier-envelope phase.By numerically solving the time-dependent Schr(o|¨)dinger equation, the high-order above-threshold ionization of asymmetric molecules in few-cycle pulses has been investigated. The resulting high-order spectra is very sensitive to the carrier-envelope phase of few-cycle pulses. Because of the existing of an asymmetric well in asymmetric molecules, the left-right asymmetry of high-energy photoelectron yield is different from the case of atoms. Using the left-right asymmetry of high-energy photoelectron yield of asymmetric molecules instead of atoms to measure the carrier-envelope phase can achieve a higher resolution.The dependence of nonsequential double ionization of Ar atoms in few-cycle pulses on the carrier-envelope phase has been investigated by numerically solving the two-electron time-dependent Schr(o|¨)dinger equation. The simulated two-electron momentum spectra exhibit asymmetry, which varies with the carrier-envelope phase. The resulting momentum distributions of the Ar²⁺ ions are in good agreement with the experimental results qualitatively, the ratio of left-right double ionization yield is very similar with the case of atoms. In addition, compared with the infinity-range interaction, the double ionization is enhanced for the short-range interaction between the two electrons.The quantum mechanical simulations of double ionization of asymmetric molecule HeH⁺ in intense laser pulses show that the two-electron momentum spectra exhibit asymmetry. This asymmetry depends on the laser intensity, i.e., double ionization mechanisms. The distinct charge configuration of HeH⁺ is responsible for the effect. According to this point, we propose an approach to control the dynamics in nonsequential double ionization process by changing the angle of the permanent dipole of asymmetric molecules relative to laser field polarization. Whereafter, we firstly demonstrate the manipulating of the direction of two-electron emission and the total double ionization yield in strong-field nonsequential double ionization with this approach. The component of the permanent dipole along the laser polarization controls the direction of two-electron emission, while the transversal component controls the recollision probability and thus the total double ionization yield.We have investigate the microscopic dynamics and energy correlation in nonsequential double ionization at laser intensities below the recollision threshold. For near-infrared wavelengths, the quantum mechanical simulations of the electron correlated momentum spectra shows several prominent features, revealing a resonant double ionization process, in which the two electrons simultaneously absorb photons of an integer number and share excess energy from the strongly correlated doubly excited states. The Coulomb repulsion between the two electrons is released into the kinetic energy in continuum states.