Let there be light

Source: The post is based on the article “Let there be light” published in “The Hindu” on 5th October 2023

What is the News?

The Nobel Prize in Physics 2023 has been awarded to Pierre Agostini, Ferenc Krausz and Anne L’Huillier for experimental methods that generate attosecond pulses of light for the study of electron dynamics in matter.

Why is it difficult to observe electrons?

Electrons, the negatively charged particles within atoms, were not directly observable by scientists initially.Instead, their properties were understood through averages. 

Imagine taking a picture of a fast-moving race car.If the camera’s exposure time is long, the image becomes blurry.But with a shorter exposure time, you get a sharper image. 

Similarly, electrons move so rapidly that they would appear blurred to a camera without the ability to capture images in attoseconds (10^-18 seconds).

How did these three scientists make their contributions?

Electron dynamics are incredibly fast, operating on the order of attoseconds, which are a billionth of a billionth of a second. 

In comparison, the movement of atoms in molecules can be studied using femtosecond pulses, which are a millionth of a billionth of a second.

By the 1980s, scientists had developed technology to create femtosecond light pulses, but they needed even shorter pulses to “see” electrons. 

Anne L’Huillier and her colleagues in France discovered a method in 1987. They passed an infrared laser beam through a noble gas, which generated overtones of light waves with wavelengths that were integer fractions of the original beam’s wavelength.

These overtones of ultraviolet light interacted with each other. When the peaks of two overtones aligned, they created more intense light through constructive interference. Conversely, when a peak aligned with a trough, they canceled each other out through destructive interference.

Researchers realized they could fine-tune this setup to create intense attosecond-long pulses of light through constructive interference. 

Pierre Agostini’s group in France successfully produced 250-attosecond light pulses in 2001, and Ferenc Krausz’s team in Austria isolated individual 650-attosecond pulses.These attosecond pulses enabled rapid experiments and measurements of electron behavior in atoms.