eTraj.jl: Trajectory-based simulation for strong-field ionization

The dynamics of light-matter interactions in the realm of strong-field ionization has been a focal point and has attracted widespread interest. We present the eTraj.jl program package, designed to implement established classical/semiclassical trajectory-based methods to determine the photoelectron momentum distribution resulting from strong-field ionization of both atoms and molecules. The program operates within a unified theoretical framework that separates the trajectory-based computation into two stages: initial-condition preparation and trajectory evolution. For initial-condition preparation, we provide several methods, including the Strong-Field Approximation with Saddle-Point Approximation (SFA-SPA), SFA-SPA with Non-adiabatic Expansion (SFA-SPANE), and the Ammosov-Delone-Krainov theory (ADK), with atomic and molecular variants, as well as the Weak-Field Asymptotic Theory (WFAT) for molecules. For trajectory evolution, available options are Classical Trajectory Monte-Carlo (CTMC), which employs purely classical electron trajectories, and the Quantum Trajectory Monte-Carlo (QTMC) and Semi-Classical Two-Step model (SCTS), which include the quantum phase during trajectory evolution. The program is a versatile, efficient, flexible, and out-of-the-box solution for trajectory-based simulations for strong-field ionization. It is designed with user-friendliness in mind and is expected to serve as a valuable and powerful tool for the community of strong-field physics.

强场电离领域内的光与物质相互作用动力学始终是核心研究焦点，受到广泛关注。本文提出了eTraj.jl程序包（eTraj.jl），该程序包旨在实现成熟的基于经典/半经典轨迹的计算方法，以求解原子与分子强场电离过程中的光电子动量分布。本程序基于统一的理论框架开发，将基于轨迹的计算流程划分为两个阶段：初始条件制备与轨迹演化。在初始条件制备环节，程序提供了多种可选方法，包括结合鞍点近似的强场近似（SFA-SPA）、带非绝热展开的SFA-SPA（SFA-SPANE）、适配原子与分子体系的阿莫索夫-德隆-克拉伊诺夫理论（ADK），以及针对分子体系的弱场渐近理论（WFAT）。在轨迹演化环节，可用方案包括采用纯经典电子轨迹的经典轨迹蒙特卡洛（CTMC），以及在轨迹演化过程中纳入量子相位的量子轨迹蒙特卡洛（QTMC）与半经典两步模型（SCTS）。本程序是一款通用、高效、灵活且开箱即用的强场电离轨迹模拟工具，设计时充分兼顾了用户友好性，有望成为强场物理领域极具价值的专业研究工具。