Update August 2017 – this article is now published in PRL, under the alternative title Molecular Frame Reconstruction Using Time-Domain Photoionization Interferometry.
Phys. Rev. Lett. 119, 083401 (2017), DOI: 10.1103/PhysRevLett.119.083401
(Feb 2017) New manuscript on the arxiv:
(Submitted on 29 Jan 2017)
Photoionization of molecular species is, essentially, a multi-path interferometer with both experimentally controllable and intrinsic molecular characteristics. In this work, XUV photoionization of impulsively aligned molecular targets (N2) is used to provide a time-domain route to “complete” photoionization experiments, in which the rotational wavepacket controls the geometric part of the photoionization interferometer. The data obtained is sufficient to determine the magnitudes and phases of the ionization matrix elements for all observed channels, and to reconstruct molecular frame interferograms from lab frame measurements. In principle this methodology provides a time-domain route to complete photoionization experiments, and the molecular frame, which is generally applicable to any molecule (no prerequisites), for all energies and ionization channels.
arxiv 1701.08432 (2017)
Supplementary material (theory, data and code) available at DOI: 10.6084/m9.figshare.4480349.
Update 28/06/17 – Now published in J. Phys. B, special issue on Correlations in Light-Matter Interactions.
Angle-resolved (AR) RABBIT measurements offer a high information content measurement scheme, due to the presence of multiple, interfering, ionization channels combined with a phase-sensitive observable in the form of angle and time-resolved photoelectron interferograms. In order to explore the characteristics and potentials of AR-RABBIT, a perturbative 2-photon model is developed; based on this model, example AR-RABBIT results are computed for model and real systems, for a range of RABBIT schemes. These results indicate some of the phenomena to be expected in AR-RABBIT measurements, and suggest various applications of the technique in photoionization metrology.
Paul Hockett 2017 J. Phys. B: At. Mol. Opt. Phys. 50 154002
Pre-print available via Authorea, DOI: 10.22541/au.149037518.89916908.
arXiv 1703.08586 (2017)
See also the recent AR-RABBIT presentation for a brief intro to this topic.
Open science – the practice of making full research projects open and accessible, from inception to publication – is an increasingly important topic, and even appearing in the popular press, particularly with regard to transparency and reproducible in research… hence open science can be viewed as the opposite of bad science.
John Arnold Made a Fortune at Enron. Now He’s Declared War on Bad Science
Open science (along with the more general notion of open data) is also part of the Canadian Government’s Open Government action plan, which includes the statement that:
The Government of Canada will maximize access to federally-funded scientific research to encourage greater collaboration and engagement with the scientific community, the private sector, and the public.
As part of our work towards open science, our articles are increasingly available on open platforms (arXiv, Authorea). And, now, good things are happening with our data too. Thanks to the Open Science Foundation (OSF) and Figshare, it’s now easy to share data, code etc. and make it citable with a DOI.
Some of our recent open science data can be found at:
Time-dependent Wavepackets and Photoionization – CS2 (2013 – present)
Our ongoing work on the calculation of time-dependent wavepackets and observables in photoionization is now collected in an OSF project (DOI: 10.17605/OSF.IO/RJMPD). Aspects of this work have previously been published, but much of the detail and methodology underlying the calculations has remained sitting on our computers. As part of our Open Science Initiative, we’re letting this data go free! Head over to the OSF project “Time-dependent Wavepackets and Photoionization – CS2” for more.
Time-resolved multi-mass ion imaging: femtosecond UV-VUV pump-probe spectroscopy with the PImMS camera (2017)
Bootstrapping to the Molecular Frame with Time-domain Photoionization Interferometry (2017)
Time Delay in Molecular Photoionization (2016)
Let your data be free!
Feb. 2017 – New article in Chemical Physics Letters:
Kwanghsi Wang(a) , Vincent McKoy(a), Paul Hockett(b), Albert Stolow(b, c, d),Michael S. Schuurman(b, d),
a A. A. Noyes Laboratory of Chemical Physics, California Institute of Technology, Pasadena, California 91125, USA
b National Research Council Canada, 100 Sussex Drive, Ottawa, Ontario K1A 0R6, Canada
c Department of Physics, University of Ottawa, ON K1N 6N5 Canada
d Department of Chemistry and Biomolecular Sciences, University of Ottawa, Ottawa, ON, K1N 6N5, Canada
- • Time-resolved photoelectron angular distributions around conical intersections are studied.
- • Ab initio multiple spawning method is applied to obtain wavepacket densities.
- • Geometry and energy dependent photoelectron matrix elements are employed.
- • Molecular and laboratory photoelectron angular distributions are used to illustrate the non-adiabatic dynamics.
- • Photoelectron spectra are compared with measured values.
We report results from a novel fully ab initio method for simulating the time-resolved photoelectron angular distributions around conical intersections in CS2. The technique employs wavepacket densities obtained with the multiple spawning method in conjunction with geometry- and energy-dependent photoionization matrix elements. The robust agreement of the calculated molecular-frame photoelectron angular distributions with measured values for CS2 demonstrates that this approach can successfully illuminate, and disentangle, the underlying coupled nuclear and electronic dynamics around conical intersections in polyatomic molecules.
UPDATE: 4th April 2017
The article is now published in the Journal of Chemical Physics, with an accompanying press release, The Inner Lives of Molecules, from AIP.
The full dataset and analysis scripts are now also available via OSF, DOI: 10.17605/OSF.IO/RRFK3.
Feb. 2017 – new article on the arXiv:
(Submitted on 2 Feb 2017)
The Pixel-Imaging Mass Spectrometry (PImMS) camera allows for 3D charged particle imaging measurements, in which the particle time-of-flight is recorded along with (x,y) position. Coupling the PImMS camera to an ultrafast pump-probe velocity-map imaging spectroscopy apparatus therefore provides a route to time-resolved multi-mass ion imaging, with both high count rates and large dynamic range, thus allowing for rapid measurements of complex photofragmentation dynamics. Furthermore, the use of vacuum ultraviolet wavelengths for the probe pulse allows for an enhanced observation window for the study of excited state molecular dynamics in small polyatomic molecules having relatively high ionization potentials. Herein, preliminary time-resolved multi-mass imaging results from C2F3I photolysis are presented. The experiments utilized femtosecond UV and VUV (160.8~nm and 267~nm) pump and probe laser pulses in order to demonstrate and explore this new time-resolved experimental ion imaging configuration. The data indicates the depth and power of this measurement modality, with a range of photofragments readily observed, and many indications of complex underlying wavepacket dynamics on the excited state(s) prepared.
arXiv 1702.00744 (2017)
Now published in JCP:
The Journal of Chemical Physics 147, 013911 (2017);
Also on Authorea, DOI: 10.22541/au.149030711.19068540
New on the arxiv:
ePSproc: Post-processing suite for ePolyScat electron-molecule scattering calculations
ePSproc provides codes for post-processing results from ePolyScat (ePS), a suite of codes for the calculation of quantum scattering problems, developed and released by Luchesse & co-workers (Gianturco et al. 1994)(Natalense and Lucchese 1999)(R. R. Lucchese and Gianturco 2016). ePS is a powerful computational engine for solving scattering problems, but its inherent complexity, combined with additional post-processing requirements, ranging from simple visualizations to more complex processing involving further calculations based on ePS outputs, present a significant barrier to use for most researchers. ePSproc aims to lower this barrier by providing a range of functions for reading, processing and plotting outputs from ePS. Since ePS calculations are currently finding multiple applications in AMO physics (see below), ePSproc is expected to have significant reuse potential in the community, both as a basic tool-set for researchers beginning to use ePS, and as a more advanced post-processing suite for those already using ePS. ePSproc is currently written for Matlab/Octave, and distributed via Github: https://github.com/phockett/ePSproc.
New paper in Optics Letters:
Optical quantum memories are an important component of future optical and hybrid quantum technologies. Raman schemes are strong candidates for use with ultrashort optical pulses due to their broad bandwidth; however, the elimination of deleterious four-wave mixing noise from Raman memories is critical for practical applications. Here, we demonstrate a quantum memory using the rotational states of hydrogen molecules at room temperature. Polarization selection rules prohibit four-wave mixing, allowing the storage and retrieval of attenuated coherent states with a mean photon number 0.9 and a pulse duration 175 fs. The 1/𝑒 memory lifetime is 85.5 ps, demonstrating a time-bandwidth product of ≈480 in a memory that is well suited for use with broadband heralded down-conversion and fiber-based photon sources.
We’ve just finished a manuscript summarising our early work with the Hololens, including data visualization and interdisciplinary work. This is a little different in flavour to our usual work, but will provide a solid foundation for more advanced work with the Hololens, including lab uses and more advanced data visualization.
Paul Hockett & Tim Ingleby
Early hands-on experiences with the Microsoft Hololens augmented/mixed reality device are reported and discussed, with a general aim of exploring basic 3D visualization. A range of usage cases are tested, including data visualization and immersive data spaces, in-situ visualization of 3D models and full scale architectural form visualization. Ultimately, the Hololens is found to provide a remarkable tool for moving from traditional visualization of 3D objects on a 2D screen, to fully experiential 3D visualizations embedded in the real world.
The manuscript is currently available on Authorea, and the arxiv.