Bootstrapping to the Molecular Frame with Time-domain Photoionization Interferometry

Bootstrapping to the Molecular Frame with Time-domain Photoionization Interferometry

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:

Bootstrapping to the Molecular Frame with Time-domain Photoionization Interferometry

 

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.

Trans jacket inscription of FBGs

Trans jacket inscription of FBGs

Using pulses from the 30fs amplified laser system in the femtolabs, and fibre writing equipment from the Fibre Photonics lab, this project focusses on developing methods for inscription of Fibre Bragg Gratings (FBGs) through the polyimide fibre cover. Through the use of short focal length acylindrical optics, the laser spot-size on the cover is much larger than in the core. This along with the very short pulses allows us to work in a regime where we can still write strong gratings through multiphoton dielectric modification, without damaging the cover (through two photon absorption).

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.

Reading today…

Reading today…

Nonlinear quantum optics mediated by Rydberg interactions

O Firstenberg, C S Adams and S Hofferberth

Published 30 June 2016© 2016 IOP Publishing Ltd
Journal of Physics B: Atomic, Molecular and Optical Physics, Volume 49, Number 15
Special Issue on Rydberg Atomic Physics

By mapping the strong interaction between Rydberg excitations in ultra-cold atomic ensembles onto single photons via electromagnetically induced transparency, it is now possible to realize a medium which exhibits a strong optical nonlinearity at the level of individual photons. We review the theoretical concepts and the experimental state-of-the-art of this exciting new field, and discuss first applications in the field of all-optical quantum information processing.

DOI: 10.1088/0953-4075/49/15/152003

Fascinating insight into the topic, which utilises the properties of Rydberg matter to enable traditional non-linear optics to cross over to the quantum regime. From the intro:

One remarkable success of advances in ultra-cold Rydberg physics is the realization of a medium with a large optical nonlinearity at the single photon level [1–3]. Highly excited Rydberg atoms bring something new to the history of optics as they enable quantum nonlinear media where photons are strongly interacting!

Recommended.

Reading today…

Reading today…

First On-Sky Fringes with an Up-Conversion Interferometer Tested on a Telescope Array

P. Darré, R. Baudoin, J.-T. Gomes, N. J. Scott, L. Delage, L. Grossard, J. Sturmann, C. Farrington, F. Reynaud, and T. A. Ten Brummelaar
Phys. Rev. Lett. 117, 233902 – Published 29 November 2016

10.1103/PhysRevLett.117.233902

The Astronomical Light Optical Hybrid Analysis project investigates the combined use of a telescope array interferometer and nonlinear optics to propose a new generation of instruments dedicated to high-resolution imaging for infrared astronomy. The nonlinear process of optical frequency conversion transfers the astronomical light to a shorter wavelength domain. Here, we report on the first fringes obtained on the sky with the prototype operated at 1.55μm in the astronomical H band and implemented on the Center for High Angular Resolution Astronomy telescope array. This seminal result allows us to foresee a future extension to the challenging midinfrared spectral domain.

This is quite interesting as an application of photon up-conversion at low-light levels – in this case for interferometric IR telescope arrays.  The demo in the paper doesn’t show any improvement on the existing configuration (i.e. no non-linear optical step), but in principle could: once one factors in not just lossy detection in the IR, but also lossy beam transport (in the conceptually similar VLTI system it’s about 10% efficient).

The header image shows fig. 1 from the paper.

Reading today…

Reading today…

Quantum imaging with undetected photons

Gabriela Barreto Lemos, Victoria Borish, Garrett D. Cole, Sven Ramelow, Radek Lapkiewicz & Anton Zeilinger

Nature 512, 409–412 (2014)

doi:10.1038/nature13586

Interferometric imaging based on photon pairs, from the intro:

Information is central to quantum mechanics. In particular, quantum interference occurs only if there exists no information to distinguish between the superposed states. The mere possibility of obtaining information that could distinguish between overlapping states inhibits quantum interference1, 2. Here we introduce and experimentally demonstrate a quantum imaging concept based on induced coherence without induced emission3, 4. Our experiment uses two separate down-conversion nonlinear crystals (numbered NL1 and NL2), each illuminated by the same pump laser, creating one pair of photons (denoted idler and signal). If the photon pair is created in NL1, one photon (the idler) passes through the object to be imaged and is overlapped with the idler amplitude created in NL2, its source thus being undefined. Interference of the signal amplitudes coming from the two crystals then reveals the image of the object. The photons that pass through the imaged object (idler photons from NL1) are never detected, while we obtain images exclusively with the signal photons (from NL1 and NL2), which do not interact with the object. Our experiment is fundamentally different from previous quantum imaging techniques, such as interaction-free imaging5 or ghost imaging6, 7, 8, 9, because now the photons used to illuminate the object do not have to be detected at all and no coincidence detection is necessary. This enables the probe wavelength to be chosen in a range for which suitable detectors are not available. To illustrate this, we show images of objects that are either opaque or invisible to the detected photons. Our experiment is a prototype in quantum information—knowledge can be extracted by, and about, a photon that is never detected.

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.