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.

由强的超短激光脉冲启动和控制的原子和分子过程是等离子体科学和相关技术中日益增长的兴趣的主题。激光诱导单个原子和分子的电离和激发，进而在等离子体介质中产生各种非线性光学现象。一种这样的现象，激光成丝，是通过激光光束的自聚焦实现的，这导致激光脉冲的剧烈收缩并在可控的距离处产生延长的细丝。部分电离等离子体是在成丝激光脉冲后留下的，它可以被后续的激光脉冲探测，并可用于各种实际应用。这项理论研究解决了演化中的灯丝-尾迹通道中的瞬时非线性光学的一个新领域；它探索了在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。这项研究将推动人们更广泛地理解在微观尺度上控制强场光-物质相互作用的方法。它还直接涉及基于细丝的、远程检测复杂混合物的多路方法的最新发展，这是许多技术应用的挑战。这与控制成丝动力学以实现大气中的远程激光有关，与开发新的阿秒脉冲和X射线脉冲源有关。这项研究涉及飞秒激光细丝尾迹通道中离子、高能自由电子和激发中性粒子的相互作用动力学，以及演化系统与探测激光脉冲的相互作用。预期的结果将为有效控制灯丝尾迹非线性光学效应奠定基础。这项任务将结合使用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模型，以及探测激光与介质耦合的密度矩阵计算来解决。其目标包括：1)建立由碰撞电离、中性和离子碰撞电子激发、解离复合、振动激发和弹性散射等相互竞争的过程驱动的丝状尾迹通道和电离栅中离子密度分布和分子/原子激发演化的预测模型；2)通过实施辅助场法和从头计算，计算离子在电离激光脉冲作用下的动态极化率和超极化率系数，并将结果应用于获得丝状尾迹通道中动态二次和四次非线性折射率的演化空间分布；以及3)预测探测激光脉冲与尾迹通道的非线性相互作用的结果，包括由电离光栅介导的双光束耦合、离子旋转复苏以及动态Rabi边带发射的可控空间光谱图案。预期的结果将应用于坦普尔大学高级光子学研究中心(CAPR)的电离相关偏振旋转、旋转-恢复光谱以及灯丝尾迹通道中的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的高次谐波(最高可达X射线)以及在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，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

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.