Probing two-path electron quantum interference in strong-field ionization with time-correlation filtering

Attosecond dynamics in strong-field tunnel ionization are encoded in intricate holographic patterns in the photoelectron momentum distributions. These patterns show the interference between two or more superposed quantum electron trajectories, which are defined by their ionization times and subsequent evolution in the laser field. We determine the ionization time separation between interfering pairs of electron orbits by performing a differential Fourier analysis on the measured momentum spectrum. We identify electron holograms formed by trajectory pairs whose ionization times are separated by less than a single quarter cycle, between a quarter cycle and half cycle, between a half cycle and three fourths of a cycle, and a full cycle apart. We compare our experimental results to the predictions of the Coulomb quantum orbit strong-field approximation (CQSFA) with significant success. We also time-filter the CQSFA trajectory calculations to demonstrate the validity of the technique on spectra with known time correlations. As a general analysis technique, the filter can be applied to all energy- and angularly resolved data sets to recover time correlations between interfering electron pathways, providing an important tool to analyze any strong-field ionization spectra. Moreover, it is independent of theory and can be applied directly to experiments, without the need of a direct comparison with orbit-based theoretical methods

Transient vibration and product formation of photoexcited CS2 measured by time-resolved x-ray scattering

We have observed details of the internal motion and dissociation channels in photoexcited carbon disulfide (CS<sub>2</sub>) using time-resolved x-ray scattering (TRXS). Photoexcitation of gas-phase CS<sub>2</sub> with a 200 nm laser pulse launches oscillatory bending and stretching motion, leading to dissociation of atomic sulfur in under a picosecond. During the first 300 fs following excitation, we observe significant changes in the vibrational frequency as well as some dissociation of the C-S bond, leading to atomic sulfur in the both <sup>1</sup>D and <sup>3</sup>P states. Beyond 1400 fs, the dissociation is consistent with primarily <sup>3</sup>P atomic sulfur dissociation. This channel-resolved measurement of the dissociation time is based on our analysis of the time-windowed dissociation radial velocity distribution, which is measured using the temporal Fourier transform of the TRXS data aided by a Hough transform that extracts the slopes of linear features in an image. The relative strength of the two dissociation channels reflects both their branching ratio and differences in the spread of their dissociation times. Measuring the time-resolved dissociation radial velocity distribution aids the resolution of discrepancies between models for dissociation proposed by prior photoelectron spectroscopy work

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 pump–probe 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 pump–probe 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

Forming a Community of Practice to Support Faculty in Implementing Course-Based Undergraduate Research Experiences

There is an urgent need to influence educational change in the methods by which science is taught. Numerous national agencies have called for science, technology, engineering, and mathematics (STEM) educational reform with recommendations to address retention and increase diversity of students in STEM disciplines. One way to address these recommendations is by replacing the widespread traditional approach to foundational laboratory courses with course-based undergraduate research experiences (CUREs). As a creative alternative to one-on-one research mentorships, CUREs scale up the research experience to reach a greater number of students, many of whom would otherwise not be able to participate in research. Increasing the adoption of CUREs in foundational chemistry laboratory courses exposes a larger, more diverse population of STEM students to research experiences. The greatest impact of these experiences occurs in populations that are traditionally underrepresented in STEM disciplines, whose college experiences are enhanced by being a part of a diverse community. A Community of Practice brings together people with a common interest or goal. This chapter describes our steps to form a Community of Practice comprised of faculty from Primarily Undergraduate Institutions, community colleges, and high schools with the goal of providing a supportive framework that lowers barriers to CURE development and implementation for faculty in foundational chemistry laboratories