On October 3, the 2023 Nobel Prize in Physics was awarded to Anne L’Huillier, Ferenc Krausz, and Pierre Agostini for making it possible to use attosecond lasers in the lab, allowing physicists to study some of the fastest known phenomena in physics — the movement of electrons. 

On the attosecond

An attosecond represents a billionth of a billionth of a second. This is an incomprehensibly small amount of time. In fact, there are more attoseconds in a single second than there have been seconds in existence since the beginning of the universe 13.8 billion years ago. 

Atoms, the particles that make up all matter, are composed of a nucleus made up of subatomic particles called protons and neutrons surrounded by electrons. The nucleus of an atom is significantly larger and bulkier than the electrons surrounding it. Atoms move and turn at a timescale of a millionth of a billionth of a second — also called a femtosecond. The electrons move 1000 times faster than atoms in a timescale that can only be observed in attoseconds. Because of how fast electrons move, directly observing them was thought to be impossible. 

Scientists use pulses of light to capture images of atoms. The fastest pulse or ‘shutter speed’ that was previously thought to be possible was in the femtoseconds timescale, which is able to capture atomic movements but not the movements of electrons. 

L’Huillier, Krausz, Agostini, and their colleagues’ pioneering research has now made it possible to generate pulses of light that are attoseconds long, and physicists can therefore directly observe electrons for the first time ever. 

Generating attosecond long pulses of light

Why is this jump from femtoseconds to attoseconds so impressive? Prior to 2001, lab lasers were not able to create wavelengths that are shorter than a femtosecond. Therefore, generating pulses of light in attoseconds was significantly more difficult.

In 1987, L’Huillier discovered that shooting an infrared laser beam at a noble gas — a really stable gas — resulted in the emission of shorter ‘overtones,’ or multiples of the initial wave. These emitted overtones can interact with each other to create pulses of varying sizes. Similar to how ripples in water originating from two different points can cancel each other out or add onto each other, waves that are superimposed on each other can add up to a giant wave when their crests align or decrease in amplitude when a trough and crest align. Therefore, by reflecting and adding up different waves of light, it is possible to create new waves that are even shorter. 

In 2001, Krausz and Agostini, in their respective labs, used this discovery to figure out an arrangement of overlapping overtones that would result in pulses that were in the attosecond timescale. Now, physicists can produce a pulse of just a few dozen attoseconds using their methods. 

Why studying electrons is important 

Having a way to directly observe electrons opens avenues in pretty much every scientific field, from electronics to medicine. Electrons are the fundamental wheel on which matter interactions turn. Chemical reactions result from electron interactions; molecular interactions in our bodies result from electron interactions. Our very phones and their touch screens use electrons.

Having a precise way to study such an important part of matter interactions opens doors to developing better technologies, better diagnoses, and more. It is also possible to no longer just observe reactions but also control them by nudging electrons using these attosecond pulses of light with unprecedented precision. 

Electrons are the gods upon which life rests, and thanks to L’Huillier, Krausz, Agostini, and their colleagues, we finally have a way to observe and precisely interact with them, which is incredible.