Tag Archives: attosecond science

Attosecond imaging technology with record high-harmonic generation

This July 21, 2021 news item on Nanowerk is all about laser pulses and tiny timescales.

Cornell researchers have developed nanostructures that enable record-breaking conversion of laser pulses into high-harmonic generation, paving the way for new scientific tools for high-resolution imaging and studying physical processes that occur at the scale of an attosecond – one quintillionth of a second [emphasis mine].

High-harmonic generation has long been used to merge photons from a pulsing laser into one, ultrashort photon with much higher energy, producing extreme ultraviolet light and X-rays used for a variety of scientific purposes. Traditionally, gases have been used as sources of harmonics, but a research team led by Gennady Shvets, professor of applied and engineering physics in the College of Engineering, has shown that engineered nanostructures have a bright future for this application.

llustration of an infrared laser hitting a gallium-phosphide metsurface, which efficiently produces even and odd high-harmonic generation. Credit: Daniil Shilkin/Provided

A July 21, 2021 Cornell University news release by Syl Kacapyr (also on EurekAlert), which originated the news item, provides more detail about the nanostructures,

The nanostructures created by the team make up an ultrathin resonant gallium-phosphide metasurface that overcomes many of the usual problems associated with high-harmonic generation in gases and other solids. The gallium-phosphide material permits harmonics of all orders without reabsorbing them, and the specialized structure can interact with the laser pulse’s entire light spectrum.

“Achieving this required engineering of the metasurface’s structure using full-wave simulations,” Shcherbakov [Maxim Shcherbakov] said. “We carefully selected the parameters of the gallium-phosphide particles to fulfill this condition, and then it took a custom nanofabrication flow to bring it to light.”

The result is nanostructures capable of generating both even and odd harmonics – a limitation of most other harmonic materials – covering a wide range of photon energies between 1.3 and 3 electron volts. The record-breaking conversion efficiency enables scientists to observe molecular and electronic dynamics within a material with just one laser shot, helping to preserve samples that may otherwise be degraded by multiple high-powered shots.

The study is the first to observe high-harmonic generated radiation from a single laser pulse, which allowed the metasurface to withstand high powers – five to 10 times higher than previously shown in other metasurfaces.

“It opens up new opportunities to study matter at ultrahigh fields, a regime not readily accessible before,” Shcherbakov said. “With our method, we envision that people can study materials beyond metasurfaces, including but not limited to crystals, 2D materials, single atoms, artificial atomic lattices and other quantum systems.”

Now that the research team has demonstrated the advantages of using nanostructures for high-harmonic generation, it hopes to improve high-harmonic devices and facilities by stacking the nanostructures together to replace a solid-state source, such as crystals.

Here’s a link to and a citation for the paper,

Generation of even and odd high harmonics in resonant metasurfaces using single and multiple ultra-intense laser pulses by Maxim R. Shcherbakov, Haizhong Zhang, Michael Tripepi, Giovanni Sartorello, Noah Talisa, Abdallah AlShafey, Zhiyuan Fan, Justin Twardowski, Leonid A. Krivitsky, Arseniy I. Kuznetsov, Enam Chowdhury & Gennady Shvets. Nature Communications volume 12, Article number: 4185 DOI: https://doi.org/10.1038/s41467-021-24450-9 Published: 07 July 2021

This paper is open access.

Attosecond science impacts femtochemistry

An Aug. 17, 2016 news item on Nanowerk reveals the latest about attoscience and femtochemistry (Note: A link has been removed),

Attosecond Science is a new exciting frontier in contemporary physics, aimed at time-resolving the motion of electrons in atoms, molecules and solids on their natural timescale. Electronic dynamics derives from the creation and evolution of coherence between different electronic states and proceeds on sub-femtosecond timescales. In contrast, chemical dynamics involves position changes of atomic centers and functional groups and typically proceeds on a slower, femtosecond timescale inherent to nuclear motion.

Nonetheless, there are exciting ways in which chemistry can hugely benefit from the technological developments pushed forward in the vibrant field of Attosecond Science. This was exploited in the work recently published by Lorenz Drescher and coworkers (“XUV transient absorption spectroscopy of iodomethane and iodobenzene photodissociation”).

An Aug. 17, 2016 (?) Forschungsverbund Berlin press release, which originated the news item, provides more detail about the work,

Attosecond pulses are generated in the process of High Harmonic Generation (HHG), in which infrared photons are upconverted to the extreme ultraviolet (XUV) frequency domain in a highly non-linear interaction of intense coherent light and matter. The short duration of attosecond pulses implies a frequency spectrum with photon energies spanning from a few electron volts (eV) to hundreds of eV. Such broad and continuous frequency spectra are ideally suited for core shell absorption measurements in molecules.

Core shell to valence shell transitions are a unique probe of molecular structure and dynamics. Core-to-valence transitions are element specific, due to the highly localized nature of core orbitals on specific atoms. On the other hand the intramolecular local environment of specific atomic sites is encoded, since an electron is lifted from a core orbital to a hole in the valence shell, affected by chemical bonding (…). Importantly, these transitions typically correspond to very short lifetimes of only a few femtoseconds. The use of ultrashort XUV pulses hence gives a new twist to the ultrafast studies of chemistry: It allows to probe chemical dynamics, initiated by a UV pump laser pulse, from the perspective of different reporter atoms within a molecule in an XUV transient absorption experiment. This is now beginning to be explored by a number of groups around the world.

In the experiment carried out by Drescher and coworkers at the MBI, photodissociation of iodomethane (CH3I) and iodobenzene (C6H5I) was studied with time-resolved XUV transient absorption spectroscopy at the iodine pre-N4,5 edge, using femtosecond UV pump pulses and XUV probe pulses from HHG (…). For both molecules the molecular core-to-valence absorption lines were found to fade immediately, within the pump-probe time-resolution. Absorption lines converging to the atomic iodine product however emerge promptly in CH3I but are time-delayed in C6H5I. In CH3I, we interpret this observation as the creation of an instantaneous new target state for XUV absorption by the UV pump pulse, which is then subject to relaxation of the excited valence shell as the molecule dissociates. This relaxation shows in a continuous shift in energy of the emerging atomic absorption lines in CH3I, which we measured in the experiment. In contrast, the delayed appearance of the absorption lines in C6H5I is indicative of a UV created vacancy, which within the molecule is initially spatially distant from the iodine reporter atom and has to first travel intramolecular before being observed. This behaviour is attributed to the dominant π → σ* UV excitation in iodobenzene, which involves the π orbital of the phenyl moiety.

While in the current work only a simplistic independent particle model was used to rationalize the observed experimental findings, MBI with its newly created theory department provides unique opportunities for joint experimental and theory studies on XUV transient absorption of photochemical processes. This will involve a new theoretical approach developed recently by researchers from MBI together with colleagues in Canada, the UK and Switzerland, which was recently submitted as a publication.

Here’s a link to and a citation for the paper,

Communication: XUV transient absorption spectroscopy of iodomethane and iodobenzene photodissociation by L. Drescher, M. C. E. Galbraith, G. Reitsma, J. Dura, N. Zhavoronkov, S. Patchkovskii, M. J. J. Vrakking, and J. Mikosch. J. Chem. Phys. 145, 011101 (2016); http://dx.doi.org/10.1063/1.4955212

This paper appears to be open access.

All about time, metronomes, and attoseconds

Apparently there’s a metronome (the world’s most accurate) which makes it possible to get slow-motion videos/movies of atoms and molecules. The Jan. 16, 2012 news item on Nanowerk offers this,

The world’s most accurate metronome keeps stroke to an incredible 10 quintillionth of a second. The device enables slow-motion pictures from the world of molecules and atoms, scientists from the Center for Free-Electron Laser Science (CFEL) in Hamburg, Germany, and the Massachusetts Institute of Technology (MIT) report. The metronome, an ultrashort pulse laser, acting as an optical flywheel, is currently the most precise clock generator on short time scales, writes the research team headed by DESY scientist Prof. Franz X. Kärtner in the journal Nature Photonics (“Optical flywheels with attosecond jitter”). CFEL is a joint venture of DESY, the German Max Planck Society and the University of Hamburg.

I find this prospect gobsmacking (quite stunning), from the news item,

The accuracy of the laser beat is ten attoseconds (quintillionth of a second), or 0.000 000 000 000 000 01 seconds. [emphasis mine] Atomic clocks achieve a higher precision, yet on longer time scales. Only with this accurate laser beat it is possible to take motion pictures of the nanocosm, as the movement of electrons in molecules and atoms take place on time scales of some 100 attoseconds to femtoseconds. [emphasis mine] “That is about the time an electron needs for orbiting a hydrogen nucleus or for the electric charge to move through a molecule during photosynthesis,” Kärtner explains. With novel light sources, so-called free-electron lasers, researchers expect fundamental new insights into those processes.

I can hardly wait to see my first nanocosm in motion. There’s no word as to when this might be possible in either the news item on Nanowerk or on the Center for Free-Electron Laser Science (CFEL) announcement page.

At the atto scale

Earlier this week, a team of Canadian scientists announced that they were able to observe a chemical bond as it broke. From the news item on physorg.com,

Scientists at the National Research Council of Canada (NRC) and the University of Ottawa (uOttawa) enjoyed a bird’s eye view of a chemical bond as it breaks.

The making and breaking of chemical bonds underlie the biochemical processes of life itself. A greater understanding of the quantum processes that lead to chemical reactions may lead to new strategies in the design and control of molecules — ultimately leading to scientific breakthroughs in health care and diagnostic medicine, quantum computing, nanotechnology, environmental science and energy.

The NRC-uOttawa team, led by Dr. David Villeneuve, achieved their feat using a technique developed several years ago at NRC in which an image was obtained of a single electron orbiting a molecule. In the current experiment, which is reported in the July 29th edition of Nature, scientists injected bromine gas into a vacuum chamber. There, an ultra brief ultraviolet light pulse caused the bromine molecules to separate into their individual atoms (a bromine molecule is composed of two bromine atoms).

A few femtoseconds later, an intense infrared laser pulse caused the molecule to emit an attosecond-duration X-ray burst that contained a snapshot of the atom’s position as the molecule fell apart and revealed how the electrons rearranged themselves.

The interference of the x-rays emitted by the two quantum states of the molecule was used to find the location of the atoms and to watch over a period of only 200 femtoseconds as it progressed from being a molecule to being two separate atoms. The experiment reached a precision below 500 zeptoseconds in clocking the emitted x-ray bursts. [emphases mine]

I’ve highlighted the units of measurement because they fascinate me in and of themselves. (I hadn’t encountered zeptos before although I have blogged about attoseconds,  May 13, 2009 posting).

Here are official designations starting with the nanoscale and dropping down to the smallest unit to date (from the US National Institute of Standards and Technology, Technology Services, Weights and Measures page),

nano, (n), meaning 10-9
pico, (p), meaning 10-12
femto, (f), meaning 10-15
atto, (a), meaning 10-18
zepto, (z), meaning 10-21
yocto, (y), meaning 10-24

If nano is the science of small, what will the others be?

Canadian attosecond researcher wins medal

The Natural Sciences and Engineering Research Council (NSERC)  awarded Dr. Paul Corkum at the University of Ottawa with $1M in funding and the Gerhard Herzberg Canada Gold Medal for Science and Engineering. Corkum’s work is in the field of attosecond science.

I looked up attosecond to find out that it is one quintillionth of a second or one thousandth of a femtosecond. I found the description of the work a little more helpful (from Attosecond science researcher wins Gerhard Herzberg Canada Gold Medal),

Dr. Paul Corkum and his team at NRC used the world’s fastest laser light pulses to capture the first image of an electron, one of the smallest bits of matter in the universe.

And this helped too,

Dr. Paul Corkum and his team … used the world’s fastest laser light pulses to capture the first image of an electron, one of the smallest bits of matter in the universe. This manipulation of electrons could lead to breakthroughs in fields as diverse as computing, engineering and medicine.

I’m still trying to find ways to describe nanotechnology and now there’s attosecond science. Not to mention synthetic biology (I’m still not sure I can define the difference between that and biotechnology). Btw, there’s a Project on Emerging Nanotechnologies event, Synthetic Biology: The Next Biotech Revolution Is Brewing on Wednesday, March 25, 2009 from 9:30 am to 10:30 am PST. It will be webcast live and posted on their website a few days later. If you’re in the Washington, DC area and want to attend please RSVP by clicking on the event title link. The event features Michael Rodemeyer from the University of Virginia. He’s the author of a report titled New Life, Old Bottles: Regulating First-Generation Products of Synthetic Biology and will be discussing the US regulatory framework for biotechnology and whether synthetic biology can be contained within that framework.