To catch an electron in the act and watch it scurry away from a pulse of light, milliseconds (thousandths of a second) just aren’t good enough. Neither are microseconds (one millionth), nanoseconds (one billionth), or even picoseconds (one trillionth).
To understand the behavior of some tiny particles and proteins, scientists are splitting time into the tiniest fractions they can — with femtoseconds and even down into attoseconds, a billionth of a billionth of a second.
At MIT, researchers are pushing the boundaries of measuring time as part of their quest to understand topological insulators (TI), a class of exotic materials discovered only a few years ago. When electrons interact with these insulators, they behave in odd ways that lead scientists to think that TIs could be used to make advanced electronics. Says MIT News:
Electrons normally have mass, just like many other fundamental particles, but when moving along the surface of TIs they move as if they were massless, like light — one of the extraordinary characteristics that give these new materials such promise for new technologies.
To understand the unusual and seemingly contradictory qualities of TIs, the MIT scientists led by Yihua Wang and Nuh Gedik wanted to watch the electrons move on and inside the material. But the only way to capture the particles’ ultra-quick motion is through pulses of femtosecond lasers, which can fire pulses of light that last for just a million of a billionth of a second.
Just how minute are those slices of time? They’re tiny fractions of a femtosecond, which itself passes in much less than the blink of an eye, MIT news explains:
In one femtosecond, light travels just 300 nanometers — about the size of the biggest particle that can pass through a HEPA filter, and just slightly larger than the smallest bacteria. Another way of thinking about the length of a femtosecond is this: One femtosecond is to one second as one second is to about 32 million years.
The femtosecond lasers worked: they fired two laser pulses — one to scatter the electrons and another to capture the image. (They call it the pump-probe technique.) The result is a series of three-dimensional images that document the electrons’ movement, and combine to form the first 3D ‘movies’ of these particles moving through TIs.
As impressive as a femtosecond laser is, though, scientists have been able to produce pulses this short for more than a decade. Pushing the boundaries of physics requires even more minuscule slices of time. Fully understanding electrons — and then even smaller particles such as quarks — will require pulses in the next range after femtoseconds — attoseconds. (The shortest pulse ever measured is now 80 attoseconds.) It may be time for zany-sounding units of time like zeptoseconds and yoctoseconds.
The work was published in Physical Review Letters this week.
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