椭圆偏振强激光场诱导分子电离过程中的缀饰态和非缀饰态  

Dressed-state and undressed-state during molecular ionization induced by elliptically polarized laser field

作　　者：刘洁[1] 郝小雷[1] LIU Jie;HAO Xiaolei(Institute of Theoretical Physics,State Key Laboratory of Quantum Optics Technologies and Devices,Shanxi University,Taiyuan 030006,China)

机构地区：[1]山西大学理论物理研究所,光量子技术与器件全国重点实验室,太原030006

出　　处：《物理学报》2025年第9期17-26,共10页Acta Physica Sinica

基　　金：国家自然科学基金(批准号:12274273)资助的课题.

摘　　要：分子强场近似(SFA)理论虽然在描述强激光场中分子的超快动力学方面取得了巨大的成功,但是理论本身存在关键的矛盾.一方面SFA基本思想要求初态为无场下的系统本征态,另一方面物理过程的空间平移不变性要求系统初态应当为激光场缀饰态,这两个相互矛盾的要求分别对应非缀饰态和缀饰态两种形式的分子SFA理论,两种理论的有效性和适用条件存在广泛的争议.本文对(椭)圆偏振激光场中N_(2)和Ne_(2)分子的电离过程进行了研究,期望能给出上述争议的解答.椭圆偏振光能有效抑制再散射过程及各种干涉效应的影响,使得电离过程更加干净,因此可以有效甄别缀饰态和非缀饰态的适用条件.本文采用SFA方法及库仑修正强场近似(CCSFA)方法计算了缀饰态和非缀饰态下不同分子轨道对应的光电子动量分布,并与已有的实验结果进行了对比.结果发现,对于Ne_(2)这样核间距较大的分子,必须采用缀饰态才能准确地描述其电离特征;而对于N_(2)这样核间距较小的分子,缀饰态描述则不适用.本文的结论为准确描述激光诱导分子超快过程及相应理论的进一步发展提供了参考.Despite the molecular strong-field approximation(SFA)theory has made remarkable achievements in describing the ultrafast dynamics of molecules in intense laser fields,there are basic inconsistencies in the theory itself.On the one hand,the basic principle of SFA requires that the initial state be an eigenstate of the system in the absence of the field,and on the other hand,the spatial translation invariance of the physical process requires that the initial state of the system be a laser-field-dressed state.These two conflicting requirements correspond to the two forms of molecular SFA theories,namely,the undressed state and the dressed state.The two theoretical validity and applicability conditions are widely disputed.In this paper,we investigate the ionization processes of N_(2) and Ne_(2) molecules in an elliptically polarized laser field and a circularly polarized laser field,aiming to solve the above-mentioned controversies.Elliptically polarized laser can efficiently suppress the re-scattering process and the influence of various interference effects,which makes the ionization process cleaner,and thus can effectively screen the applicable conditions for the dressed and undressed states.We calculate the photoelectron momentum distributions corresponding to different molecular orbitals in the dressed and undressed states by using the SFA and the Coulomb-corrected strong-field approximation and compare them with previous experimental results.For molecules with large nuclear spacing such as Ne_(2),we find that the dressed state is necessary to accurately characterise their ionization,however,for molecules with small nuclear spacing such as N_(2),the dressed state description is inapplicable.The conclusions of this work provide a reference for accurately describing laser-induced molecular ultrafast processes and further developing corresponding theories and molecular ultrafast imaging schemes.

关 键 词：椭圆偏振激光场 分子电离 缀饰态 光电子动量分布 

分 类 号：O562.4[理学—原子与分子物理]