15 research outputs found
Dissecting Sub-Cycle Interference in Photoelectron Holography
Multipath holographic interference in strong-field quantum tunnel ionization
is key to revealing sub-Angstrom attosecond dynamics for molecular movies. This
critical sub-cycle motion is often obscured by longer time-scale effects such
as ring-shaped patterns that appear in above-threshold ionization (ATI). In the
present work, we overcome this problem by combining two novel techniques in
theory and experimental analysis: unit-cell averaging and time-filtering data
and simulations. Together these suppress ATI rings and enable an unprecedented
highly-detailed quantitative match between strong-field ionization experiments
in argon and the Coulomb-quantum orbit strong-field approximation (CQSFA)
theory. Velocity map images reveal fine modulations on the holographic
spider-like interference fringes that form near the polarization axis. CQSFA
theory traces this to the interference of three types of electron pathways. The
level of agreement between experiment and theory allows sensitive determination
of quantum phase differences and symmetries, providing an important tool for
quantitative dynamical imaging in quantum systems.Comment: 13 Pages, 8 figure
Multi-channel photodissociation and XUV-induced charge transfer dynamics in strong-field-ionized methyl iodide studied with time-resolved recoil-frame covariance imaging
The photodissociation dynamics of strong-field ionized methyl iodide (CH3I) were probed using intense extreme ultraviolet (XUV) radiation produced by the SPring-8 Angstrom Compact free electron LAser (SACLA). Strong-field ionization and subsequent fragmentation of CH3I was initiated by an intense femtosecond infrared (IR) pulse. The ensuing fragmentation and charge transfer processes following multiple ionization by the XUV pulse at a range of pumpâprobe delays were followed in a multi-mass ion velocity-map imaging (VMI) experiment. Simultaneous imaging of a wide range of resultant ions allowed for additional insight into the complex dynamics by elucidating correlations between the momenta of different fragment ions using time-resolved recoil-frame covariance imaging analysis. The comprehensive picture of the photodynamics that can be extracted provides promising evidence that the techniques described here could be applied to study ultrafast photochemistry in a range of molecular systems at high count rates using state-of-the-art advanced light sources.</p
Femtosecond pulse parameter estimation from photoelectron momenta using machine learning
Deep learning models have provided huge interpretation power for image-like data. Specifically, convolutional neural networks (CNNs) have demonstrated incredible acuity for tasks such as feature extraction or parameter estimation. Here we test CNNs on strong-field ionization photoelectron spectra, training on theoretical data sets to 'invert' experimental data. Pulse characterization is used as a 'testing ground', specifically we retrieve the laser intensity, where 'traditional' measurements typically lead to 20% uncertainty. We report on crucial data augmentation techniques required to successfully train on theoretical data and return consistent results from experiments, including accounting for detector saturation. The same procedure can be repeated to apply CNNs in a range of scenarios for strong-field ionization. Using a predictive uncertainty estimation, reliable laser intensity uncertainties of a few percent can be extracted, which are consistently lower than those given by traditional techniques. Using interpretability methods can reveal parts of the distribution that are most sensitive to laser intensity, which can be directly associated with holographic interferences. The CNNs employed provide an accurate and convenient ways to extract parameters, and represent a novel interpretational tool for strong-field ionization spectra
Multi-channel photodissociation and XUV-induced charge transfer dynamics instrong-field-ionized methyl iodide studiedwith time-resolved recoil-framecovariance imaging
The photodissociation dynamics of strong-field ionized methyl iodide (CH3I) were probed using intense extreme ultraviolet (XUV) radiation produced by the SPring-8 Angstrom Compact free electron LAser (SACLA). Strong-field ionization and subsequent fragmentation of CH3I was initiated by an intense femtosecond infrared (IR) pulse. The ensuing fragmentation and charge transfer processes following multiple ionization by the XUV pulse at a range of pumpâprobe delays were followed in a multi-mass ion velocity-map imaging (VMI) experiment
Multi-channel photodissociation and XUV-induced charge transfer dynamics in strong-field-ionized methyl iodide studied with time-resolved recoil-frame covariance imaging
The photodissociation dynamics of strong-field ionized methyl iodide (CH3I) were probed using intense extreme ultraviolet (XUV) radiation produced by the SPring-8 Angstrom Compact free electron LAser (SACLA). Strong-field ionization and subsequent fragmentation of CH3I was initiated by an intense femtosecond infrared (IR) pulse. The ensuing fragmentation and charge transfer processes following multiple ionization by the XUV pulse at a range of pumpâprobe delays were followed in a multi-mass ion velocity-map imaging (VMI) experiment. Simultaneous imaging of a wide range of resultant ions allowed for additional insight into the complex dynamics by elucidating correlations between the momenta of different fragment ions using time-resolved recoil-frame covariance imaging analysis. The comprehensive picture of the photodynamics that can be extracted provides promising evidence that the techniques described here could be applied to study ultrafast photochemistry in a range of molecular systems at high count rates using state-of-the-art advanced light sources