Intense light-matter interactions for source development

Intense light-matter interactions for source development

Novel wave-mixing techniques can be used for the generation of ultrashort pulses in the VUV (<200nm) region of the spectrum.  This project will investigate the development of new light sources, based on our existing expertise and capabilities at 5th and 6th harmonic generation. These processes make use of a high-power 800nm femtosecond laser on the back-end, and involve multiple stages of non-linear wave-mixing in crystals and gases. The generation of tunable VUV is of particular interest.

For more on our work with VUV so far, see:
Time-resolved multi-mass ion imaging: femtosecond UV-VUV pump-probe spectroscopy with the PImMS camera
Ruaridh ForbesVarun MakhijaKévin VeyrinasAlbert StolowJason W. L. LeeMichael BurtMark BrouardClaire VallanceIain WilkinsonRune LaustenPaul Hockett
arXiv 1702.00744 (2017)The Journal of Chemical Physics 147, 013911 (2017), DOI: http://dx.doi.org/10.1063/1.4978923

 

Press Release: The Inner Lives of Molecules

Press Release: The Inner Lives of Molecules

Our latest work with the PImMS camera, femtosecond VUV pulses, and velocity-map imaging, has been picked up for a press release by AIP.

The Inner Lives of Molecules

New method takes 3-D images of molecules in action

WASHINGTON, D.C., April 4, 2017 — Quantum mechanics rules. It dictates how particles and forces interact, and thus how atoms and molecules work — for example, what happens when a molecule goes from a higher-energy state to a lower-energy one. But beyond the simplest molecules, the details become very complex.

“Quantum mechanics describes how all this stuff works,” said Paul Hockett of the National Research Council of Canada. “But as soon as you go beyond the two-body problem, you can’t solve the equations.” So, physicists must rely on computer simulations and experiments.

Now, he and an international team of researchers from Canada, the U.K. and Germany have developed a new experimental technique to take 3-D images of molecules in action. This tool, he said, can help scientists better understand the quantum mechanics underlying bigger and more complex molecules.

The new method, described in The Journal of Chemical Physics, from AIP Publishing, combines two technologies. The first is a camera developed at Oxford University, called the Pixel-Imaging Mass Spectrometry (PImMS) camera. The second is a femtosecond vacuum ultraviolet light source built at the NRC femtolabs in Ottawa.

Mass spectrometry is a method used to identify unknown compounds and to probe the structure of molecules. In most types of mass spectrometry, a molecule is fragmented into atoms and smaller molecules that are then separated by molecular weight. In time-of-flight mass spectrometry, for example, an electric field accelerates the fragmented molecule. The speed of those fragments depends on their mass and charge, so to weigh them, you measure how long it takes for them to hit the detector.

Most conventional imaging detectors, however, can’t discern exactly when one particular particle hits. To measure timing, researchers must use methods that effectively act as shutters, which let particles through over a short time period. Knowing when the shutter is open gives the time-of-flight information. But this method can only measure particles of the same mass, corresponding to the short time the shutter is open.

The PImMS camera, on the other hand, can measure particles of multiple masses all at once. Each pixel of the camera’s detector can time when a particle strikes it. That timing information produces a three-dimensional map of the particles’ velocities, providing a detailed 3-D image of the fragmentation pattern of the molecule.

To probe molecules, the researchers used this camera with a femtosecond vacuum ultraviolet laser. A laser pulse excites the molecule into a higher-energy state, and just as the molecule starts its quantum mechanical evolution — after a few dozen femtoseconds –another pulse is fired. The molecule absorbs a single photon, a process that causes it to fall apart. The PImMS camera then snaps a 3-D picture of the molecular debris.

By firing a laser pulse at later and later times at excited molecules, the researchers can use the PImMS camera to take snapshots of molecules at various stages while they fall into lower energy states. The result is a series of 3-D blow-by-blow images of a molecule changing states.

The researchers tested their approach on a molecule called C2F3I. Although a relatively small molecule, it fragmented into five different products in their experiments. The data and analysis software is available online as part of an open science initiative, and although the results are preliminary, Hockett said, the experiments demonstrate the power of this technique.

“It’s effectively an enabling technology to actually do these types of experiments at all,” Hockett said. It only takes a few hours to collect the kind of data that would take a few days using conventional methods, allowing for experiments with larger molecules that were previously impossible.

Then researchers can better answer questions like: How does quantum mechanics work in larger, more complex systems? How do excited molecules behave and how do they evolve?

“People have been trying to understand these things since the 1920s,” Hockett said. “It’s still a very open field of investigation, research, and debate because molecules are really complicated. We have to keep trying to understand them.”

Text reproduced from AIP.

The article, Time-resolved multi-mass ion imaging: femtosecond UV-VUV pump-probe spectroscopy with the PImMS camera, is now published in the Journal of Chemical Physics, and also available via the arXiv 1702.00744 and Authorea (original text), DOI: 10.22541/au.149030711.19068540.

The full dataset and analysis scripts are available via OSF, DOI: 10.17605/OSF.IO/RRFK3.

Time-resolved multi-mass ion imaging: femtosecond UV-VUV pump-probe spectroscopy with the PImMS camera

Time-resolved multi-mass ion imaging: femtosecond UV-VUV pump-probe spectroscopy with the PImMS camera

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:

Time-resolved multi-mass ion imaging: femtosecond UV-VUV pump-probe spectroscopy with the PImMS camera

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);
DOI: http://dx.doi.org/10.1063/1.4978923

Also on Authorea, DOI: 10.22541/au.149030711.19068540

 

 

PImMS camera with VUV light

PImMS camera with VUV light

UPDATE April 2017 – Some of this work is now published, and data is also available, see Time-resolved multi-mass ion imaging: femtosecond UV-VUV pump-probe spectroscopy with the PImMS camera for details.

Last week was a busy week, with Prof. Claire Vallance (and two colleagues) visiting to help with technology transfer for our Direct Ion Detection project, based on their previous work in this area. As well as preparing some scintillator coatings, we also had the opportunity to try out another flavour of the new detector technologies they’ve been developing, in the form of the time-resolved PImMS camera. The goal for future detector development is to combine these technologies for a single, on-chip, ion detection solution.

The images below show the camera attached to our velocity-map imaging (VMI) chamber and VUV source.


The endless possibilities of space (pt II)

The endless possibilities of space (pt II)

Not the most scientifically exciting post, granted, but how can you think about the new before clearing out the old…?  And, as a bonus, it’s ridiculously satisfying to take down old set-ups which haven’t been touched for some time.

In this space, the new VUV set-up will be created.

It will be beautiful.

And then there will be some physics.

Reading today…

Reading today…

Vacuum-ultraviolet to infrared supercontinuum in hydrogen-filled photonic crystal fiber

Optica, Vol. 2, Issue 4, pp. 292-300 (2015)
doi: 10.1364/OPTICA.2.000292

A nice demonstration of ultra-broadband supercontinuum generation, right down into the VUV range for the first time, based around a kagomé fibre.

VUV chambers, mk. II

VUV chambers, mk. II

New vacuum chambers for generation of light  in the vacuum ultraviolet (VUV) range (<190 nm, e.g. 5th, 6th and 7th harmonics of an 800 nm field).

Milled from a single piece of aluminium, breadboard mount points, and ports for light, vacuum and motion control.

Modular, shiny, beautiful.