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Chris Sparling

Chronological feed of everything captured from Chris Sparling.

tweet / Apr 14

Some of my worst decisions in life and business came after asking smart, well-meaning mentors for advice. Advice is often like being given the perfect recipe; but your pantry’s full of different ingr

Some of my worst decisions in life and business came after asking smart, well-meaning mentors for advice. Advice is often like being given the perfect recipe; but your pantry’s full of different ingredients. Different timing. Different team. Different tools. And once someone gives advice, they get invested in you following it. If you don’t, they think you didn’t listen. If you do, and it backfires; well, that’s on you. Stories, on the other hand, don’t come with strings. They let you hear what someone actually did, and figure out what fits your situation. Ask for stories.

article / Apr 14

About - Chris Sparling

I'm Chris Sparling. I've spent years in the entrepreneurial world, working my way through various tech ventures. I served as the CFO at MetaLab.

article / Apr 14

Tiny - Chris Sparling

There's a lot online about the company, but I wanted to have a resource on my blog to note some of the key things. ... Chris Sparling on Patron ...

paper / Apr 14

Revisiting the inverse Abel integral for reconstructing velocity-map images

The velocity-map imaging (VMI) technique is used near ubiquitously throughout the study of gas-phase photophysics and chemical dynamics. Many VMI experiments rely on numerical reconstruction techniques to recover the full three-dimensional (3D) velocity distribution of photoproducts from the two-dimensional (2D) geometric projection – the Abel transform of the distribution – that is recorded in a typical experiment. The simplest mathematical approach for this reconstruction procedure is through use of the inverse Abel integral transform. Historically, though, this approach has performed poorly on real experimental data, and so the VMI community has devoted much effort into the development of alternative inversion strategies that avoid direct use of the integral. In this article, we challenge this firmly held belief, and show instead what advantages can be realised through this approach. Unlike many other competing approaches, the reconstruction technique presented here, which we refer to as the modified Abel integral transform (MAIT), does not require the lengthy pre-computation time for a large basis set or any manually adjustable regularisation parameters. Examples involving simulated and real experimental data are used to demonstrate the efficacy of our new approach. This method is shown to perform similarly to the most popular alternative strategies for extracting photoproduct angular distributions, and have a significant advantage over them when handling data with high levels of background noise, in particular.

paper / Apr 14

Non-Dichroic Enantio-Sensitive Chiroptical Spectroscopy

Chiroptical effects using circularly polarized light produce signals that change sign when switching either molecular handedness (enantiosensitivity) or the light helicity (circular dichroism). Here, we break this enantiosensitive-and-dichroic paradigm by measuring a new type of chiroptical signal which is enantiosensitive but not dichroic. We photoionize chiral molecules using a strong laser field and detect the three-dimensional photoelectron momentum distribution. The non-dichroic, enantiosensitive asymmetry is encoded in octupolar and higher multipolar terms in the photoelectron angular distribution, which appear in multiphoton ionization with elliptically polarized fields or cross polarized two-color fields. The robustness of the enantiosensitivity with respect to the relative phase between the vectorial components of the ionizing field represents an example of symmetry protection, and opens unexplored opportunities for imaging ultrafast dynamics in chiral molecules, such as enantiosensitive photoelectron spectroscopy with bright squeezed vacuum states.

paper / Apr 14

Decoupling structural molecular dynamics from excited state lifetimes using few-femtosecond ultraviolet resonant dispersive waves

Optical sources exploiting resonant dispersive wave (RDW) emission are set to revolutionize ultrafast science. We demonstrate this approach by investigating excited state dynamics in morpholine using time-resolved photoelectron imaging. Excitation at 250 nm was achieved via RDW emission inside a helium-filled capillary fibre which, when combined with a short 800 nm probe, realized an instrument response of just 11 ± 2 fs. Two pathways initiate N–H bond fission: an extremely fast (<10 fs) process and a frustrated mechanism (380 fs) with hindered electronic ground state access. Photoelectron angular distributions also indicate average molecular geometry evolving on an intermediate (~100 fs) timescale. This clean distinction between population lifetimes and structural dynamics is enabled by the excellent temporal resolution inherent in RDW-based sources. Electronic structure and nonadiabatic surface hopping calculations support our data interpretation, and the synergy between experiment and theory is vital for developing a complete mechanistic picture. Resonant dispersive wave (RDW) emission enables tunable few-femtosecond UV pulses which can be useful for ultrafast science. Here, the authors investigate ultrafast relaxation and structural evolution of morpholine with enhanced temporal resolution, following excitation via RDWs.