Strong Field and Ultrafast Atomic and Molecular Processes

这个项目的重点是从理论上理解强相干辐射与原子和分子的相互作用，包括与可能具有很少光学周期的超短激光脉冲的相互作用。这类过程通常很难处理，因为通常必须非微扰地处理与激光场和原子分子势的电子相互作用，此外，短脉冲相互作用必须与时间相关地描述。最近的工作涉及解决短程势中的弱束缚电子与强激光场的相互作用，结果非常准确地描述了最近在强激光场中负离子分离的实验。这将扩展到用含时微扰理论另外处理弱阿秒或极少飞秒脉冲的存在。对于任意强度的激光脉冲，中性原子靶的库仑场效应将通过直接求解含时薛定谔方程来考虑。有效距离法在很大程度上是解析的，它允许简单地扫描激光频率、强度、偏振、脉冲宽度和载波包络相位的参数空间。然后，含时薛定谔方程的完全数值直接解将聚焦于中性原子情况下参数空间中最感兴趣的区域，这些区域是最常用的实验研究的。建议研究的过程包括：增强高次谐波平台强度的新方法，这是目前产生阿秒脉冲所必需的；研究使用短而少的周期脉冲来控制电子波包的散射，这是所有强场过程中产生平台特征的关键；以及研究库仑场对椭圆偏振激光在阈值以上的电离角分布的影响，以及在多通道阈值下增强强场过程中平台结构的强度。

This project focuses on understanding theoretically the interaction of intense coherent radiation with atoms and molecules, including intereactions with ultrashort laser pulses having possibly few optical cycles. Such processes are in general difficult to treat because electronic interactions with both laser fields and atomic and molecular potentials must in general be treated non-perturbatively, and in addition short pulse interactions must be described timedependently.Recent work has involved the solution of a weakly bound electron in a short-range potentialinteracting with an intense laser field essentially exactly and the results describe very accuratelyrecent experiments for negative ion detachment in intense laser fields. This will be extended to treat in addition the presence of weak attosecond or few femtosecond pulses by means of time-dependent perturbation theory. Coulomb field effects for neutral atom targets will be incorporated by direct solution of the time-dependent Schrdinger equation for a laser pulse (or pulses) of arbitrary intensity. The effective range approach, which is largely analytic, permits a simple scan of the parameter space of laser frequency, intensity, polarization, pulse duration, and carrier envelope phase. The fully numerical direct solution of the time dependent Schrdinger equation will then focus on the most interesting regions of the parameter space for the case of neutral atoms, which are most commonly studied experimentally. Processes proposed for study include novel means of enhancing the intensities of high-order harmonic plateaus, which are currently essential for producing attosecond pulses; investigating the use of short, few cycle pulses to controlrescattering of electron wave packets, which is crucial for production of plateau features in allstrong field processes; and investigating the influence of Coulomb fields on above thresholdionization angular distributions by elliptically polarized laser light and on enhancing the intensities of plateau structures in strong field processes at multichannel thresholds.