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:
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.
Supplementary material (theory, data and code) available at DOI: 10.6084/m9.figshare.4480349.
Photoionization is a complex quantum mechanical process, with a range of interfering channels playing a role in even the simplest case. For problems in quantum metrology and sensing, a detailed understanding of the process is desirable for accurate measurements; quantum control is also a possible outcome of such understanding. New research in this area will build on recent cutting-edge work at NRC (see below), which probed the fundamental quantum physics of photoionization in atoms and molecules, and metrology work which demonstrated the retrieval of electron wavefunctions via interferometric time-domain measurements.
Four areas of photoionization interferometry are the target of current research:
- Metrology and control with rotational wavepackets.
- Metrology and control with shaped laser pulses.
- Quantum dynamics probed via photoionization interferometry.
- Fundamental properties of photoion and photoelectron coherence.
Depending on interests and experience, project work will be in one (or more) of these areas.
An introduction to this topic, and recent work, can be found in Paul’s DAMOP 2017 talk Phase-sensitive Photoelectron Metrology (below), and via our blog.
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.
See also the recent AR-RABBIT presentation for a brief intro to this topic.
The above image shows simulated velocity map images (left, middle) and angle and time-resolved measurements (right) for angle-resolved RABBIT measurements. In this type of measurement, XUV and IR pulses are combined, and create a set of 1 and 2-photon bands in the photoelectron spectrum. The presence of multiple interfering pathways to each final photoelectron band (energy) results in complex and information rich interferograms, with both angle and time-dependence.
A manuscript detailing this work is currently in preparation, and a recent presentation detailing some aspects of the work can be found on Figshare.
Update 24th March – new manuscript, Angle-resolved RABBIT: theory and numerics, pre-print available.
UPDATE March 2016 – The article has been chosen for the JPB Highlights of 2015 selection, which features articles selected for their “outstanding quality and impact within the field”. The articles in the collection will be open access for the year.
Our recent paper on coherent control & quantum metrology is now published in J. Phys. B:
Coherent control of photoelectron wavepacket angular interferograms
P Hockett, M Wollenhaupt and T Baumert
J. Phys. B: At. Mol. Opt. Phys. 48 (2015) 214004.
Coherent control over photoelectron wavepackets, via the use of polarization-shaped laser pulses, can be understood as a time and polarization-multiplexed process, where the final (time-integrated) observable coherently samples all instantaneous states of the light–matter interaction. In this work, we investigate this multiplexing via computation of the observable photoelectron angular interferograms resulting from multi-photon atomic ionization with polarization-shaped laser pulses. We consider the polarization sensitivity of both the instantaneous and cumulative continuum wavefunction; the nature of the coherent control over the resultant photoelectron interferogram is thus explored in detail. Based on this understanding, the use of coherent control with polarization-shaped pulses as a methodology for a highly multiplexed coherent quantum metrology is also investigated, and defined in terms of the information content of the observable.
The work is part of the special issue on Coherence and Control in the Quantum World.
UPDATE Nov. 2015 – Chosen for the cover of the 14th November 2015 print edition.
Two new articles, on quantum metrology via polarization-shaped pulses (mostly theory) and maximum-information photoelectron metrology via tomographic measurements (mostly experiment), have just been published in PRA.
P. Hockett, M. Wollenhaupt, C. Lux, and T. Baumert
Phys. Rev. A 92, 013411 – Published 13 July 2015
(also available at arXiv:1503.08247 (2015))
Phys. Rev. A 92, 013412 – Published 13 July 2015
(also available at arXiv:1503.08308 (2015))