The Royal Swedish Academy of Sciences announced that the 2023 Nobel Prize in Physics will be awarded to Pierre Agostini, Ferenc Kraus and Anne Lullier for their experimental method of generating attosecond light pulses It is used to study the electron dynamics of matter and provides new tools for humans to explore the electronic world within atoms and molecules.
Agostini is a professor at Ohio State University in the United States; Krause is the director of the Max Planck Institute for Quantum Optics in Germany and a professor at the University of Munich in Germany; Lullier is a professor at Lund University in Sweden.
A hummingbird can beat its wings 80 times per second, and at this time the hummingbird’s wings are completely invisible to the human eye.
Humans can use high-speed cameras to capture phenomena and details that cannot be tracked by the naked eye. The faster the action, the higher the shutter speed of the photo is required to capture the moment.
If we look at the atomic level, we will find that atoms move incredibly fast. In molecules, atoms move and rotate in units of quadrillionths of a second (10-15 seconds, also known as femtoseconds).
However, if we focus on the electrons inside the atom, femtoseconds can no longer catch up with the movement of the electrons. On the femtosecond scale, electron motion appears blurry—electrons move and change speeds between 1 and hundreds of attoseconds. 1 attosecond = 10-18 seconds. What is this concept?
The number of attoseconds contained in 1 second is equivalent to the number of seconds contained in the entire age of the universe (1018 seconds)!
So, how to capture traces of attoseconds? This requires the help of laser pulse technology.
Light is composed of waves, which are vibrations in electric and magnetic fields. Light moves faster than anything else in a vacuum. Different wavelengths of light show different colors. For example: red light has a wavelength of 700 nanometers and a width of Equivalent to 1/100 of a hair.
In the past, the wavelength of ordinary lasers could not be lower than femtoseconds, which was considered the limit of laser pulses. However, scientists are not satisfied with this.
Any waveform can be formed using enough sizes, wavelengths and amplitudes. Shorter pulses can be made by combining more shorter wavelengths. To observe electron motion at the atomic scale requires short enough light pulses, which means combining short waves of many different wavelengths.
1987, Annie? Lullier conducted an interesting experiment. She used femtosecond lasers to illuminate some rare gases and found that these gases would emit light of many different colors. She discovered that when a femtosecond laser passes inside an atom, it can push electrons in the gas around, just like playing with a glass ball. When the laser passes through, the electrons will return to their original positions and at the same time release the energy they just obtained in the form of light. The different degrees of “twitching” of the electrons when the laser passes through will make the wavelengths of these harmonic lights different.
This discovery has scientists excited. If you superimpose these harmonic light combinations, you can create the effect of alternating variations and darkening, like a shutter in a camera. In this way, they can use this light pulse to observe the movement of electrons.
However, it takes a long time from theoretical conception to experimental success. It wasn’t until 2001 that Pierre Agostini and his French research team successfully created and studied a series of continuous light pulses, like a train with carriages. They used some special gear and techniques to put “pulse trains” together with delayed portions of the original laser pulses to see how the overtones combined with each other. They also measured the duration of the pulses in the “pulse train” and successfully generated pulsed light lasting 250 attoseconds, which is equivalent to achieving a shutter speed of four quadrillionths of a second!
Meanwhile, Ferenc Krauz and his team in Austria worked on a technique that could achieve a single pulse, like a carriage decoupling from a train and switching to another track. They successfully isolated a pulse of light lasting 650 attoseconds.
Chinese scientists also attach great importance to the research of attosecond light pulses. In 2013, Wei Zhiyi’s research group generated and measured an isolated attosecond pulse of 160 attoseconds for the first time in China. It is currently developing further towards shorter pulse width, higher energy and higher repetition frequency.
Now, people have access to the attosecond world, and these short pulses of light can be used to study the movement of electrons. Today scientists can generate light pulses as low as tens of attoseconds, and the technology continues to evolve.
With attosecond pulses, it is possible to measure the time it takes for an electron to be pulled away from an atom and study the relationship between the time it takes for an electron to be pulled away from the atom and how tightly the electron is bound to the nucleus. At present, attosecond pulse technology has been used to explore detailed physical processes of atoms and molecules, and is expected to be applied in condensed matter physics, atomic and molecular physics, chemistry, biomedicine, information, energy and other fields.

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