2023 Nobel Prize in physics: Seeing electrons in brief flashes of light

Subject: Science and Tech

Section: Msc

Source: TH

Context:

The 2023 Nobel Prize for Physics was shared by three scientists—Pierre Agostini, Ferenc Krausz and Anne L’Huillier—for their “experimental methods that generate attosecond pulses for the study of electron dynamics in matter.”

Attosecond:

An attosecond (symbol as) is a unit of time in the International System of Units (SI) equal to 1×10¹⁸of a second (one quintillionth of a second).
- For comparison, an attosecond is to a second what a second is to about 31.71 billion years.
- An attosecond is equal to 1000 zeptoseconds, or 1⁄1000 of a femtosecond.

Attophysics:

Attosecond physics, also known as attophysics, is a branch of physics that deals with light-matter interaction phenomena wherein attosecond (10¹⁸ s) photon pulses are used to unravel dynamical processes in matter with unprecedented time resolution.
- Attosecond physics gives us the opportunity to understand mechanisms that are governed by electrons.
Their experiments have allowed scientists to produce ultra-short pulses of light, with which they can finally ‘see’ directly into the super-fast world of electrons.

Why electrons weren’t ‘seen’ before:

Electrons which are negatively charged particles of an atom, move very fast in the nucleus of an atom. To see the sharper and clear movement of electrons we need a camera with exposure time to the order of attoseconds.

How fast is electron dynamics?

The movement of an atom in a molecule can be studied with the very shortest pulses produced by a laser. These movements and changes in the atoms occur on the order of femtoseconds—a millionth of a billionth of a second. But electrons are lighter and interact faster, in the attosecond realm.
All light consists of waves of electric and magnetic energy. Each wave has a sinusoidal shape—starting from a point, going up to a peak, dipping into a trough, and finally getting back to the same level as the starting point.
By the 1980s scientists produced light pulses whose duration was a few femtoseconds. But seeing electrons required an even shorter flash of light and scientists were unable to produce a pulse of light shorter than a femtosecond.

How can even shorter pulse be created?

In 1987, Anne L’Huillier and her colleagues noticed the ‘overtones’ (waves of light whose wavelength was an integer fraction of the beam) after passing an infrared laser beam through a noble gas.

How is an attosecond pulse created?

Physicists found that the overtones emitted were in the form of ultraviolet light. As multiple overtones were created in the gas, they began to interact with each other.
- When the peak of one overtone merges with the peak of another, they produce an overtone of greater intensity, through constructive interference. But when the peak of an overtone merges with the trough of another, they cancel each other out, in destructive interference.
Scientists realized that it should be possible to create intense pulses of light each a few attoseconds long (due to constructive interference), with destructive interference ensuring that they didn’t last for longer.
In 2001,Pierre Agostini and his research group in France successfully produced and investigated a series of 250-attosecond light pulses, or a pulse train.
In the same year, Ferenc Krausz and his team in Austria developed a technique to separate an individual 650-attosecond pulse from a pulse train.
Using that, the researchers were able to measure the energy of some electrons released by some krypton atoms.

What are the applications of attosecond physics?

It allows scientists to capture ‘images’ of activities that happen in incredibly short time spans.
Scientists can use such pulses to explore short-lived atomic and molecular processes implicated in fields like materials science, electronics, and catalysis.
For medical diagnostics,attosecond pulses can be used to check for the presence of certain molecules based on their fleeting signatures.
These pulses could also be used to develop faster electronic devices, and better telecommunications, imaging, and spectroscopy.