STM-D-0920Paper2015Published and peer-reviewed

Coherent control of plasma dynamics by feedback-optimized wavefront manipulation

Z.-H. He · B. Hou · G. Gao · V. Lebailly · J. A. Nees · R. Clarke · K. Krushelnick · A. G. R. Thomas

Summary and citation · read the original at the source

In one page

Shine a short, intense laser pulse into a gas and it strips electrons loose and drives a wave through the plasma behind it — a wave whose electric field can accelerate electrons far harder than any metal cavity. The trouble is that nobody can calculate in advance what shape the incoming light should have, because the plasma reshapes the beam as the beam makes the plasma. So the Michigan group of Z.-H. He and colleagues stopped calculating and started searching. They put a deformable mirror in the beam, let an evolutionary algorithm bend it, and used the experiment’s own output — the electron beam itself — as the score to be improved. The mirror finds the wavefront no one could have written down. Applied to two experiments, electron acceleration in a plasma wave and self-compression of the pulse by the gas it is ionising, the search improved the beam’s charge, its divergence and its emittance by orders of magnitude. Steering a plasma by choosing the phase of the light is coherent control, now demonstrated on plasma.

Why it matters hereChapter 9 is about plasma that organises itself into structures, and this is the paper that shows those structures can be steered from outside by shaping the light that makes them, rather than merely observed. It is also chapter 10’s principle in a working laboratory: what is being adjusted is the phase front, and phase is the handle.

What it claims

01Plasmas generated by an intense laser pulse support coherent structures, such as a large-amplitude wakefield, and those structures can determine the outcome of an experiment.Abstract, sentence 1; Physics of Plasmas 22, 056704 (2015)
Published and peer-reviewed
02The method is coherent control by feedback-optimised wavefront manipulation: a deformable mirror shapes the phase front of the driving laser pulse, and the experimental outcome is used directly as the feedback signal in an evolutionary algorithm that searches for the optimum.Abstract, sentences 2 and 3
Published and peer-reviewed
03The same method was applied to two different experiments — acceleration of electrons in laser-driven plasma waves, and self-compression of optical pulses induced by the nonlinearity of ionisation — so the control technique is not specific to one target.Abstract, sentence 4
Published and peer-reviewed
04Manipulating the laser wavefront produced orders of magnitude of improvement in the electron beam properties: the peak charge, the beam divergence and the transverse emittance.Abstract, sentence 5
Published and peer-reviewed
05What to watch: the authors state that the demonstration of coherent control for plasmas opens new possibilities for future laser-based accelerators and their applications, and the measurement that turns that into engineering is whether a feedback-shaped wavefront holds a laser-plasma accelerator stable shot after shot at high repetition rate, on beam charge, divergence and emittance together, rather than optimising a single campaign.Abstract, final sentence
What to watch
06The improvement is not simply a matter of making the sharpest focus: in the group’s companion paper the highest-quality vacuum focal spot produced a greatly inferior electron beam, and the winning wavefronts were instead the particular laser phases that steer the plasma wave into a final state with optimal accelerating fields — which is what makes this coherent control rather than alignment.Companion paper, He, Hou, Lebailly, Nees, Krushelnick and Thomas, Coherent control of plasma dynamics, Nature Communications 6, 7156 (2015), abstract; preprint arXiv 1501.04117
Published and peer-reviewed

The way in

https://doi.org/10.1063/1.4921159SOURCE NOT REACHED IN FULL. AIP holds the article closed; Unpaywall and OpenAlex both report no open version, and the only repository record OpenAlex lists — the STFC ePubs entry, record 32640466 — carries the bibliographic details and the funding acknowledgement but no file. No text of the article is reproduced here. The summary and the first five claims are written from the authors’ own abstract as deposited with the article and indexed by OpenAlex, and from the Crossref record, which fixes the venue as Physics of Plasmas volume 22, issue 5, article 056704, May 2015; the sixth claim comes from the abstract of the companion paper named in its locator, which is open. Locators therefore point to sentences of the abstract rather than to numbered sections. The title as publishers and indexes carry it ends in a stray footnote mark, the letter a followed by a closing bracket, which is a reference to the article’s own first footnote and not part of the title; it is dropped here. Author names are given exactly as Crossref records them, with the affiliations there placing all but one author at the Center for Ultrafast Optical Science and the Department of Physics at the University of Michigan, Ann Arbor, and V. Lebailly at Polytech Paris-Sud, Université Paris-Sud, Orsay. The work was supported by the United States National Science Foundation under grants 0935197 and 1054164.

How to cite it

Z.-H. He, B. Hou, G. Gao, V. Lebailly, J. A. Nees, R. Clarke, K. Krushelnick, A. G. R. Thomas (2015) Coherent control of plasma dynamics by feedback-optimized wavefront manipulation. doi:10.1063/1.4921159

Where it sits in the curriculum

Plasmoids, charge clusters and the orbs Scalar waves and the field behind the fields