Visualization of atomic and molecule excitation/ionization processes with ultra-short (attosecond) and optical gated (femtosecond) laser pulses and study of high harmonic generation (HHG) in a filament

使用超短（阿秒）和光门控（飞秒）激光脉冲可视化原子和分子激发/电离过程，并研究灯丝中的高次谐波产生 (HHG)

基本信息

批准号：
RGPIN-2017-06181
负责人：
Witzel, Bernd
金额：
$ 1.53万
依托单位：
Université Laval
依托单位国家：
加拿大
项目类别：
Discovery Grants Program - Individual
财政年份：
2020
资助国家：
加拿大
起止时间：
2020-01-01 至 2021-12-31
项目状态：
已结题

来源：
https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=711463
关键词：
Visualization atomic molecule excitation ionization

项目摘要

In the past year, we have been able to generate with our Femtolaser V system (800 nm, 5 mJ, 1 kHz, CEP stabilized) high harmonic spectra up to 130 eV pulses in a filament created in a differential pumped gas cell. We plan to extend this region with our TOPAS system. We have already measured CEP (carrier envelope phase) stabilized laser pulses of 2400 nm up to 1mJ. The setup will allow us to extend the HHG cut-off region up to 400 eV. The scientific goals are divided into 3 different axes. In a first project we want to study excitation processes and inner-shell ionization as well as inner shell excitation processes of molecules and atoms. Therefore we will use (femtosecond) pump - (sub-femtosecond) probe experiments and measure the electron spectrum of both laser pulses together. We will obtain in the low energy part of the electron spectrum the ATI (above threshold ionization) spectrum of the femtosecond pump laser, the high energy part will measure the probe pulse. We are only limited to laser intensities where the energy distribution of electrons from the ATI-spectrum does not overlap the electron energy spectrum from the probe pulse. This restriction can be overcome when the momentum distribution from the electrons of the pump and probe pulse is different. We want to upgrade our VMI (velocity map imaging) spectrometer to measure both contributions. With this technique we will be able to study inner-shell ionization, inner shell excitation processes of molecules and atoms. This offers us complementary information to HHG experiments. In a second project we want to visualize processes taking place in a sub cycle of a laser. We have started atom ionization/excitation experiments with polarization gated laser pulses and have been the first to publish VMI electron spectra. These laser pulses are composed of circularly polarized sections at the leading and trailing edges of the pulse and of an experimentally defined linearly polarized central part. The central part can be restricted down to a fraction of an optical cycle. Processes taking place only at linear polarization can be restricted in time down to a half cycle. We want to use this method for different wavelengths as well as ionization processes with laser pulses with sub-cycle linear polarization. We want to better understand HHG generation in a filament and continue the experiments we have started recently with 800 nm. Later we will extend these experiments to other wavelengths generated by the TOPAS system. There we want to study the effect of atomic/molecular resonances as well as the possibility to amplify a HHG signal in a filament. Measurements, where the intensity as well as the wavelength dependent HHG spectra are taken at the same time will be an ideal tool to visualize atom/molecular high laser field physics.

在过去的一年中，我们已经能够使用 Femtolaser V 系统（800 nm、5 mJ、1 kHz、CEP 稳定）在差动泵气室中创建的灯丝中生成高达 130 eV 的高次谐波光谱。我们计划通过 TOPAS 系统扩展该区域。我们已经测量了 2400 nm 至 1 mJ 的 CEP（载波包络相位）稳定激光脉冲。该装置将使我们能够将 HHG 截止区域扩展至 400 eV。科学目标分为 3 个不同的轴。在第一个项目中，我们想要研究激发过程和内壳层电离以及分子和原子的内壳层激发过程。因此，我们将使用（飞秒）泵浦-（亚飞秒）探针实验并一起测量两个激光脉冲的电子光谱。我们将在电子谱的低能部分获得飞秒泵浦激光器的ATI（高于阈值电离）谱，高能部分将测量探测脉冲。我们仅限于激光强度，其中来自 ATI 谱的电子能量分布与来自探测脉冲的电子能谱不重叠。当泵浦和探测脉冲的电子的动量分布不同时，可以克服这个限制。我们想要升级我们的 VMI（速度图成像）光谱仪来测量这两种贡献。通过这项技术，我们将能够研究分子和原子的内壳层电离、内壳层激发过程。这为我们提供了 HHG 实验的补充信息。在第二个项目中，我们希望可视化激光子周期中发生的过程。我们已经开始使用偏振门控激光脉冲进行原子电离/激发实验，并率先发布了 VMI 电子光谱。这些激光脉冲由脉冲前缘和后缘处的圆偏振部分以及实验定义的线偏振中心部分组成。中心部分可以限制为光周期的一小部分。仅在线性偏振下发生的过程可以在时间上被限制到半个周期。我们希望将此方法用于不同波长以及具有子周期线性偏振的激光脉冲的电离过程。我们希望更好地了解灯丝中 HHG 的产生，并继续我们最近开始的 800 nm 实验。稍后我们将把这些实验扩展到 TOPAS 系统产生的其他波长。我们想要研究原子/分子共振的影响以及放大灯丝中 HHG 信号的可能性。同时进行强度和波长相关的 HHG 光谱的测量将是可视化原子/分子高激光场物理的理想工具。