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: 1806594
• 负责人: Dmitri Romanov
• 金额: $ 22.56万
• 依托单位: Temple University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2018
• 资助国家: 美国
• 起止时间: 2018-08-15 至 2023-01-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1806594&HistoricalAwards=false
• 关键词: Transient; Optical; Nonlinearities; Engendered; Femtosecond

Atomic and molecular processes initiated and controlled by intense, ultrashort laser pulses are a subject of steadily growing interest in plasma science and related technology. The laser-induced ionization and excitation of individual atoms and molecules beget in turn various nonlinear optical phenomena in the plasma medium. One such phenomenon, laser filamentation, is enabled by self-focusing of the laser beam, which results in a drastic contraction of the laser pulse and generation of an extended filament at a controllable stand-off distance. Partially ionized plasma is left in the wake of the filamenting laser pulse; it can be probed by subsequent laser pulses and is open to various practical applications. This theoretical research addresses a new realm of transient nonlinear optics in evolving filament-wake channels; it explores longer-lasting optical consequences of strong-field ionization occurring in a relatively dense plasma. The research will advance broader understanding of means to control strong-field light-matter interaction on a microscopic scale. It also directly addresses recent developments of filament-based, multiplex methods of remote detection of complex mixtures, which is a challenge with many technological applications. It is related to control of filamentation dynamics with the aim of remote lasing in the atmosphere, and to developing new sources of attosecond and X-ray pulses.This research concerns the interrelated dynamics of ions, energetic free electrons, and excited neutrals in wake channels of femtosecond laser filaments, as well as the interaction of the evolving system with probe laser pulses. The expected outcomes will form a basis for effective control of filament-wake nonlinear optical effects. The task will be addressed using a combination of ab initio calculations for nonlinear response of individual ions, kinetic modeling of inhomogeneous ionized-gas medium evolution, and density matrix calculations for probe laser coupling with the medium. The objectives include:1) developing predictive models of the evolution of ion density profiles and molecular/atomic excitation in filament wake channels and ionization gratings, which is driven by competing processes of impact ionization, impact electronic excitation of neutrals and ions, dissociative recombination, vibrational excitation, and elastic scattering; 2) calculating dynamic polarizability and hyperpolarizability coefficients of ions in the wake of the ionizing laser pulse (when perturbative approaches become applicable) by implementing the auxiliary-field approach and ab initio calculations, and applying the results to obtain evolving spatial profiles of dynamic quadratic and quartic nonlinear refractive indices in filament wake channels; and3) predicting outcomes of nonlinear interactions of probe laser pulses with the wake channels, including two-beam coupling mediated by ionization gratings, ionic rotational revivals, and controllable spatial-spectral patterns of dynamic Rabi sideband emission. The expected results will be applied to experiments on ionization-related polarization rotation, rotational-revival spectroscopy, and dynamic Rabi sidebands in filament wake channels at the Center for Advanced Photonics Research (CAPR) at Temple University. Further, the ionization-specific nonlinear effects are related to recent experiments on bright higher harmonic generation (up to X-rays) in highly ionized gases and on igniter-heater processes in filament wake 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.

由强超短激光脉冲引发和控制的原子和分子过程是等离子体科学和相关技术日益增长的兴趣的主题。激光诱导的电离和单个原子和分子的激发反过来在等离子体介质中产生各种非线性光学现象。其中一种现象是激光成丝，它是通过激光束的自聚焦实现的，这会导致激光脉冲的急剧收缩并在可控的隔离距离处产生延长的灯丝。部分电离的等离子体留在丝状激光脉冲后面；它可以通过后续激光脉冲进行探测，并可用于各种实际应用。这项理论研究探讨了演化灯丝尾流通道中瞬态非线性光学的新领域；它探索了相对密集的等离子体中发生的强场电离的更持久的光学后果。该研究将促进对微观尺度上强场光与物质相互作用的控制方法的更广泛理解。它还直接解决了基于灯丝的复杂混合物远程检测的多重方法的最新发展，这对许多技术应用来说是一个挑战。它与控制丝状动力学有关，目的是在大气中远程发射激光，并与开发新的阿秒和 X 射线脉冲源有关。这项研究涉及尾流通道中离子、高能自由电子和激发中性粒子的相互关联的动力学飞秒激光丝，以及不断发展的系统与探测激光脉冲的相互作用。预期结果将为有效控制灯丝尾迹非线性光学效应奠定基础。该任务将通过结合单个离子的非线性响应的从头计算、非均匀电离气体介质演化的动力学建模以及探针激光与介质耦合的密度矩阵计算来解决。目标包括：1) 开发灯丝尾流通道和电离光栅中离子密度分布和分子/原子激发演变的预测模型，这是由碰撞电离、中性子和离子的碰撞电子激发、解离重组的竞争过程驱动的，振动激发和弹性散射； 2) 通过实施辅助场方法和从头计算计算离子在电离激光脉冲之后的动态极化率和超极化系数（当微扰方法适用时），并应用结果来获得动态二次和灯丝尾流通道中的四次非线性折射率； 3）预测探测激光脉冲与尾流通道的非线性相互作用的结果，包括由电离光栅介导的两束耦合、离子旋转复兴和动态拉比边带发射的可控空间光谱模式。预期结果将应用于天普大学高级光子学研究中心 (CAPR) 灯丝尾流通道中与电离相关的偏振旋转、旋转复兴光谱和动态拉比边带的实验。此外，电离特定的非线性效应与最近在高电离气体中产生明亮高次谐波（直至 X 射线）以及灯丝尾流通道中的点火器加热器过程的实验有关。该奖项反映了 NSF 的法定使命，并被视为值得通过使用基金会的智力优点和更广泛的影响审查标准进行评估来支持。

项目成果

Intrapulse impact processes in dense-gas femtosecond laser filamentation

浓密气体飞秒激光成丝中的脉冲内冲击过程

• DOI: 10.1103/physreva.97.063411
• 发表时间: 2018
• 期刊: Physical Review A
• 影响因子: 2.9
• 作者: Romanov, Dmitri A.;Gao, Xiaohui;Gaeta, Alexander L.;Levis, Robert J.
• 通讯作者: Levis, Robert J.

Control of the excited-to-ionized atoms ratio in a dense gas in the wake of an intense femtosecond laser pulse

在强飞秒激光脉冲后控制稠密气体中激发原子与电离原子的比率

• DOI: 10.1103/physreve.105.045210
• 发表时间: 2022
• 期刊: Physical Review E
• 影响因子: 2.4
• 作者: Bajpai, Suyash;Romanov, Dmitri A.
• 通讯作者: Romanov, Dmitri A.

Strong-field molecular alignment mediated by nonadiabatic charge localization

• DOI: 10.1103/physreva.100.063423
• 发表时间: 2019-11
• 期刊: Physical Review A
• 影响因子: 2.9
• 作者: D. Romanov;R. Levis

Excitation gratings in cross-beam filament wake channels in a dense argon gas: Formation, control, and Rabi sideband manifestation

稠密氩气中交叉束灯丝尾流通道中的激发光栅：形成、控制和拉比边带表现

• DOI: 10.1103/physreve.107.065202
• 发表时间: 2023
• 期刊: Physical Review E
• 影响因子: 2.4
• 作者: Bajpai, Suyash;Romanov, Dmitri A.
• 通讯作者: Romanov, Dmitri A.

Delayed ionization and excitation dynamics in a filament wake channel in a dense-gas medium

稠密气体介质中灯丝尾流通道的延迟电离和激发动力学

• DOI: 10.1103/physreva.102.013110
• 发表时间: 2020
• 期刊: Physical Review A
• 影响因子: 2.9
• 作者: Romanov, Dmitri A.;Levis, Robert J.
• 通讯作者: Levis, Robert J.