Transient Optical Nonlinearities Engendered by Femtosecond Laser Filamentation in Gases

气体中飞秒激光丝产生的瞬态光学非线性

• 批准号: 2309247
• 负责人: Dmitri Romanov
• 金额: $ 20万
• 依托单位: Temple University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2023
• 资助国家: 美国
• 起止时间: 2023-08-01 至 2026-07-31
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2309247&HistoricalAwards=false
• 关键词: Transient; Optical; Nonlinearities; Engendered; Femtosecond

In an intense, ultrashort laser pulse, the electric field magnitude can reach and exceed characteristic atomic values to produce a partially ionized, nonequilibrium plasma in the pulse wake. Interaction of such pulses with gas media offers an opportunity to take direct control of electrons in the system, and to engage the system in highly nonlinear processes with lasting outcomes. This research project addresses the transitional regime in which the electrons released by the strong-field ionization during the laser pulse become actively interacting with neighbor atoms. The project will concentrate on transient nonlinear optics in the controllable filament-wake channels; the expected results will be linked to a number of current and upcoming experimental activities. The research will advance knowledge of intense laser-matter interactions, a topic of considerable interest for physics, chemistry, and coherent control communities. It also has many technological applications, such as remote lasing in the atmosphere, and developing new sources of attosecond and X-ray pulses. The research activity at the Center for Advanced Photonics Research (CAPR) at Temple University attracts a large number of students at graduate and undergraduate levels, including broad participation of underrepresented groups. These students receive training in high-technology areas of femtosecond laser systems and the related fields of high-volume parallel computations. The project aims at exploring and harnessing the physical mechanisms that create and control a transient alternative state of medium in a filament wake channel and thus determine its nonlinear-optical manifestations. Delayed nonlinear effects are manifest in many recent measurements, including higher harmonics generation, igniter-heater processes, and giant Rabi sideband emission from the channels. The task will be addressed using a combination of ab initio calculations for the nonlinear response of individual ions, kinetic description of the evolution of the inhomogeneous excited medium, and density matrix calculations for probe laser coupling with this medium. The objectives include: (i) developing a predictive description of filament channel formation in a relatively dense gas medium, as driven by the competing processes of inverse Bremsstrahlung on neutrals, impact ionization, and collisional excitation, toward exploring pulse-shape control of the resulting excited system; (ii) tracing evolution of electronic degrees of freedom in the filament wake channels, including structured channels with finite ionization/excitation gratings, as driven by thermalized electrons engaged in collisional processes and affected by Penning ionization and also by dissociative recombination and vibrational excitation in the case of molecular gases; the expected output being the spatio-temporal patterns of the evolving ion density profiles and molecular/atomic excitation; (iii) calculating dynamic polarizability and hyperpolarizability coefficients of ions in the wake of the laser pulse (when perturbative approaches become applicable) by implementing the auxiliary-field approach and ab initio calculations to obtain the evolving dynamic quadratic and quartic nonlinear refractive indices in filament wake channels and ionization gratings; and (iv) investigating hallmark nonlinear interactions of probe pulses with the wake channels and predicting the patterns of molecular rotational revival induced via the transient nonadiabatic charge redistribution mechanism, the patterns of frequency-domain mapping of ionic rotational revivals, and controllable spatial-spectral patterns of dynamic Rabi sideband emission from structured channels.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

在强烈的超短激光脉冲中，电场幅度可以到达并超过特征性原子值，以在脉冲唤醒中产生部分电离的非平衡等离子体。这种脉冲与加油媒体的相互作用提供了一个机会，可以直接控制系统中的电子，并使系统参与具有持久结果的高度非线性过程。该研究项目探讨了激光脉冲期间强场电离释放的电子的过渡状态与邻居原子积极相互作用。该项目将集中在可控的丝效率频道中的瞬态非线性光学元件上；预期的结果将与许多当前和即将进行的实验活动有关。这项研究将提高人们对强烈的激光互动的了解，这是对物理，化学和连贯控制社区感兴趣的话题。它还具有许多技术应用，例如大气中的远程激光，并开发了新的Attosond和X射线脉冲来源。坦普尔大学高级光子学研究中心（CAPR）的研究活动吸引了许多研究生和本科级别的学生，包括代表性不足的群体的广泛参与。这些学生接受了飞秒激光系统的高科技领域的培训以及大容量平行计算的相关领域。该项目旨在探索和利用从细丝唤醒通道中创建和控制暂时替代状态的物理机制，从而确定其非线性光学表现。延迟的非线性效应在许多最近的测量中都表现出来，包括从通道产生更高的谐波，点火器过程和巨型Rabi边带发射。将使用从头算计算的组合来解决该任务，以解决单个离子的非线性响应，对不均匀激发培养基的演变的动力学描述以及与该介质探针激光偶联的密度矩阵计算。这些目标包括：（i）在相对密集的气体介质中对细丝通道形成的预测描述，这是由Bremsstrahlung反向的中性，影响电离和碰撞激发的竞争过程所驱动的，以探索对产生的激发系统的脉冲控制； （ii）追踪灯丝唤醒通道中电子自由度的演变，包括具有有限电离/激发光栅的结构化通道，这是由从事碰撞过程的热元电子驱动的，并受到支头电离的影响，也受到分离性重置和振动的影响。预期的输出是不断发展的离子密度曲线和分子/原子激发的时空模式； （iii）通过实施激光脉冲（当扰动方法变得适用时）来计算离子的动态极化率和超极化系数，并通过实施辅助场方法和从头启动计算，以获得不断发展的动态四次和Quartic Quadratic和Quartic Quartic Quartic Quartic和Quartic的非线性折射式射击循环循环循环和离子式循环量的数量，并获得了离子化频道和离子化度量。 （iv）研究探针脉冲与唤醒通道的标志性非线性相互作用，并通过瞬态非耐绝热电荷重新分布机制，预测分子旋转复兴的模式，频率旋转旋转的频率分析模式，以及可控的空间范围内的范围内的动态统一范围内的动态统一的范围。使用基金会的知识分子优点和更广泛的审查标准，被认为值得通过评估来支持。