EAST LANSING, Mich. (AP) - Compared with Harold Edgerton’s electronic stroboscope, the mechanical shutters on even the fastest cameras moved at a glacial pace.
The microsecond flashes of light from the device Edgerton began working on in the 1920s as a graduate student at MIT sliced time thinner, making visible a world that happened too fast for the naked eye to register.
Edgerton’s iconic photographs revealed the architecture of milk droplets, hummingbirds frozen in flight, bullets at the instants they tore through apples and light bulbs and playing cards.
The microscope that Chong-Yu Ruan’s laboratory is developing at Michigan State University works on similar principles, though his objects of interest are far smaller and the seconds sliced even narrower, according to the Lansing State Journal ( https://on.lsj.com/1nJWIPN ).
It is fast enough to capture the rupture or formation of a chemical bond, the fleeting deformation of a single molecule.
Which has the potential to refine or remake our understanding of the basic mechanisms of chemistry, to open up new possibilities in materials science and medicine and nanotechnology.
Imaging materials in transformation, capturing the process of change, “is really important for understanding the inner workings of micro- and nanostructures,” Ruan said.
“This allows you to look at many open questions that people have been debating over the years.”
Conventional electron microscopes can produce images at atomic scales, of course. The problem is that those images require millisecond-long exposures or longer.
A millisecond is a fraction of the blink of an eye (the average eye blink lasts about 300 milliseconds), but “it’s like a billion years for a molecule,” said Ruan, who is a professor in the Department of Physics and Astronomy.
The final images are averages, akin to the way a human eye sees the fluttering of a dragonfly’s wing or a pencil wobbled in the hand until it appears to bend.
Electron microscopes typically use a filament to emit the electrons needed for imaging. They come out at random.
Ruan’s Ultrafast Electron Microscope, a cascade of wires and tubes, foil-wrapped parts and control modules that takes up of Ruan’s laboratory, uses a femtosecond laser to trigger the electron pulses.
A femtosecond is 0.000000000000001 seconds. Put differently, a femtosecond is to a second what a second is to 32 million years.
The laser with its ultrafast pulses is Ruan’s stroboscope.
Imaging technologies have allowed us to see faster than our own eyes since former California governor Leland Stanford hired Eadweard Muybridge to photographically settle the question of whether all four of a racehorse’s hooves leave the ground simultaneously at some point during its gallop.
On a June day in 1878, with a dozen cameras hooked up to trip wires strung across a racetrack, Muybridge showed that they did.
His cameras, state of the art at the time, managed all 12 shots in the less than a second.
But faster targets require faster speeds. The femtosecond, “actually really matches the time scale of molecular motion,” Ruan said. It takes about 10 femtoseconds for a molecular bond to break and form.
Much of what we know about what happens at the smallest scales is inference, from the minute deformations and interactions that make photosynthesis possible to the way that proteins recognize other molecules to the point of minuteness at which a material starts to lose the properties it has in bulk, when lead stops acting like lead or gold like gold.
“Having the ability to understand the event as it happens is very important,” Ruan said.
MSU has applied for a patent on the microscope. He’s working now to make it more robust, to turn it into “a turn-key device, as much as we can.”
He sees it being manufactured as an add-on to existing electron microscopes, a way to update and repurpose costly but aging equipment, for as little $500,000. (An electron microscope typically costs between $1 million and $10 million.)
In a sense, Ruan’s work on the microscope began in the early 2000s, when he was a post-doctoral researcher at the California Institute of Technology working with Ahmed Zewail, who received the Nobel Prize in chemistry for his pioneering work of fundamental chemical reactions using ultrashort laser flashes.
Zewail’s lab is still working on similar problems in microscopy, though the approach is slightly different.
“There is a growing community of people who are working in this direction,” said Hrvoje Petek, a University of Pittsburgh physicist who conducts research ultrafast microscopy, though, given the costs and the present funding climate and the particular expertise involved “only a few groups in the United States have the capability.”
“The work that Chong-Yu is doing combines the best parts of the lasers and the electron-based techniques,” he said. “It’s, in a sense, a marriage of techniques and coming together of different communities, which is starting to enable research in these time and spatial scales.”
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Information from: Lansing State Journal, https://www.lansingstatejournal.com
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