Strong Field and Ultrafast Atomic and Molecular Processes

本项目侧重于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周期的超短激光脉冲的相互作用。这样的过程通常很难处理，因为与激光场以及原子和分子势的电子相互作用通常必须以非摄动的方式处理，此外，短脉冲相互作用必须以时间依赖性的方式描述。最近的工作涉及到一个弱束缚电子在短距离电位下与强激光场基本准确地相互作用的解决方案，其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。这将被扩展到用时间相关的微扰理论来处理弱阿秒或少数飞秒脉冲的存在。中性原子靶的库仑场效应将通过直接解任意强度激光脉冲的时变薛定谔方程来考虑。有效距离方法，很大程度上是解析的，允许对激光频率、强度、极化、脉冲持续时间和载波包络相位的参数空间进行简单扫描。时间相关薛定谔方程的完全数值直接解将集中在中性原子情况下参数空间中最有趣的区域，这是最常在实验中研究的。提出的研究过程包括提高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；研究使用短周期脉冲来控制电子波包的再散射，这对于在所有强场过程中产生平台特征至关重要；利用椭圆偏振激光研究库仑场对上述阈值化角分布的影响，以及对多通道阈值下强场过程中平台结构强度增强的影响。

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.