# Nobel Prize for Physics: blink and you'll miss it

Experiments capturing the 'shortest of moments' were recognised this year...
06 October 2023

## EGG TIMER

Reporting on this year's Nobel Prize for Physics, Will Tingle:

Electrons are fundamental to electricity, magnetism, and processes in the cell, to name a few things. But they are very very small and very very fast. Anyone with a camera will tell you that taking a photo of a moving object with a long shutter speed means you get nothing but a blur. So, to have any hope of seeing electrons, you need a very short pulse of light. And that’s why this year’s Nobel Prize for Physics goes to three people: French-Swedish physicist Anne L'Huillier, French scientist Pierre Agostini and Hungarian-born Ferenc Krausz. With their powers combined, they have demonstrated how to create pulses of light so short that they can observe the way in which electrons move.

How short? Attosecond short. A billionth of a billionth of a second. There are more attoseconds in one second than there are seconds in the current age of the universe. How could you possibly hope to capture any sort of image in that short of a timeframe?

Well, you need to do some clever stuff with light.

Light is an electromagnetic wave. So the shortest pulse of light must consist of at least one full oscillation of the electromagnetic field.

Imagine a sine wave: that’s up, down, then up again. Traditional lasers can create a one wavelength pulse just fine.

But these lasers typically operate in the near-infrared region of the electromagnetic spectrum, where the wavelength is much longer than the scale of atoms. So seeing electrons is out of the question. A much shorter wavelength is needed.

The breakthrough came when it was discovered that an infrared laser, passed through gaseous atoms, interacts with these atoms and causes overtones.

Overtones are waves that complete a number of oscillations for each oscillation in the original wave, meaning they have a shorter wavelength.

Under the right conditions, the cycles of these overtones coincide, like when the indicator lamps in a queue of waiting cars suddenly all appear to be blinking in sync.

The scientists managed to synchronise the higher frequency overtones generated when their infrared pulses interacted with the gas atoms; the result is pulses of light with a much higher frequency.

And this is what allowed them to observe electrons at intervals that are small enough for them not to be blurred.

So why does this matter? Well, to understand something, you need to know where it is. And being able to pulse light for such a short period of time makes this possible for the world of electrons inside atoms and molecules.

It takes electrons 150 billion billionths of a second to go around the nucleus of a hydrogen atom. Before this breakthrough, we could only see the outline of an atom’s nucleus, but now we have the ability to see electron positions around atoms. And who knows, we could even start to manipulate where electrons go, which could have huge implications for stuff like solar energy.

Congratulations to Anne, Pierre, and Ferenc for their hard earned prize, and also thanks to Ioan Notingher of Nottingham University for helping me understand the science, which, I would argue, is an equally impressive task!