Jonathan C. T. Barnard

Attosecond impulsive stimulated X-ray Raman scattering in liquid water

Oliver Alexander, Felix Egun, Laura Rego, Ana Martinez Gutierrez et autres

We report the measurement of impulsive stimulated x-ray Raman scattering in neutral liquid water. An attosecond pulse drives the excitations of an electronic wavepacket in water molecules. The process comprises two steps: a transition to core-excited states near the oxygen atoms accompanied …

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Observation of recollision-based high-harmonic generation in liquid isopropanol and the role of electron scattering

Oliver Alexander, Jonathan C. T. Barnard, Esben Witting Larsen, Timur Avni et autres

We report extreme-ultraviolet high-harmonic generation (HHG) from liquid isopropanol, extending up to 50 eV, when using 1800-nm carrier envelope phase stable pulses of 1.8 cycles with intensities below the laser breakdown threshold. We study the mechanism of the harmonic emission through its …

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Optical control of ultrafast structural dynamics in a fluorescent protein

Christopher D. M. Hutchison, James M. Baxter, Ann E. Fitzpatrick, Gabriel Dorlhiac et autres

The photoisomerization reaction of a fluorescent protein chromophore occurs on the ultrafast timescale. The structural dynamics that result from femtosecond optical excitation have contributions from vibrational and electronic processes and from reaction dynamics that involve the crossing through a conical intersection. The …

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Delivery of stable ultra-thin liquid sheets in vacuum for biochemical spectroscopy

Jonathan C. T. Barnard, Jacob P. Lee, Oliver Alexander, Sebastian Jarosch et autres

The development of ultra-thin flat liquid sheets capable of running in vacuum has provided an exciting new target for X-ray absorption spectroscopy in the liquid and solution phases. Several methods have become available for delivering in-vacuum sheet jets using different nozzle designs. …

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Interaction of an intense few-cycle infrared laser pulse with an ultrathin transparent liquid sheet

Clément Ferchaud, Sebastian Jarosch, Timur Avni, Oliver Alexander et autres

We experimentally study the interaction between intense infrared few-cycle laser pulses and an ultrathin (∼2 µm) flat liquid sheet of isopropanol running in vacuum. We observe a rapid decline in transmission above a critical peak intensity of 50 TW/cm2 of the initially …

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The mechanism of high harmonic generation in liquid alcohol

Oliver Alexander, Jonathan C. T. Barnard, Esben Witting Larsen, Timur Avni et autres

The observation of non-perturbative harmonic emission in solids from ultrashort laser pulses [1] sparked a wave of studies [2,3] as a probe of charge carrier dynamics in solids under strong fields and a route to extreme ultraviolet (XUV) attosecond photonic devices [4]. …

Attosecond coherent electron motion in Auger-Meitner decay

Siqi Li, Taran Driver, Philipp Rosenberger, Elio G. Champenois et autres

In quantum systems, coherent superpositions of electronic states evolve on ultrafast time scales (few femtoseconds to attoseconds; 1 attosecond = 0.001 femtoseconds = 10 −18 seconds), leading to a time-dependent charge density. Here we performed time-resolved measurements using attosecond soft x-ray pulses …

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Electronic Population Transfer via Impulsive Stimulated X-Ray Raman Scattering with Attosecond Soft-X-Ray Pulses

Jordan T. O’Neal, Elio G. Champenois, Soléne Oberli, Razib Obaid et autres

Free-electron lasers provide a source of x-ray pulses short enough and intense enough to drive nonlinearities in molecular systems. Impulsive interactions driven by these x-ray pulses provide a way to create and probe valence electron motions with high temporal and spatial resolution. …

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Micrometer-thickness liquid sheet jets flowing in vacuum

Gediminas Galinis, J. Strucka, Jonathan C. T. Barnard, Avi Braun et autres

Thin liquid sheet jet flows in vacuum provide a new platform for performing experiments in the liquid phase, for example X-ray spectroscopy. Micrometer thickness, high stability, and optical flatness are the key characteristics required for successful exploitation of these targets. A novel …

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Planar transmission lines for soil water measurements

Christopher E. Bassey, Jonathan C. T. Barnard

A comparative evaluation of the propagation characteristics of a conventional time domain reflectometry (TDR) probe and a planar (coplanar) transmission line is presented. Numerical analysis is done using quasi-static design equations obtained by conformal mapping. Results show that the coplanar line exhibits …

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Rydberg Terms of the CH3 Radical

Jonathan C. T. Barnard, A. B. F. Duncan

Spectroscopic terms are calculated for two of the three observed Rydberg series in CH3. One-center SCF functions of CH3+, determined by Joshi are used for the core orbitals. The molecular geometry of CH3+ is assumed to be unchanged for the Rydberg states. …

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Rydberg Terms of Acetylene

Elwood W. Greene, Jonathan C. T. Barnard, A. B. F. Duncan

It is assumed that two observed Rydberg series in acetylene correspond to (ns) and (nd) orbital excitation. Calculations in a one-electron approximation support the assumption in both cases. The core is assumed to be frozen and linear and interatomic distances unchanged from …

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