A fully optical attoclock to image tunnelling wavepackets

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Attoclocks, or attosecond clocks, are instruments that can measure time intervals on the attosecond scale by measuring the time it takes for electrons to tunnel out of atoms. The attosecond procedure was introduced in 2008 by Ursula Keller.

A new, all-optical attoclock has recently been developed by researchers. This clock could be used to collect time-resolved measurements in Condensed-matter systems, which have never been achieved before.

Ihar Babushkin, one of the researchers who carried out the study, saidTunneling is an inherently quantum-mechanical process. The field can be made so strong that it can tear off electrons from atoms.

The process of tunnelling happens very quickly. Physicists tried to test the hypothesis that during tunneling electrons travel faster than light by using existing attoclock measurement tools.

The current fastest time that can be measured is around one second.

Researchers used to try to catch electrons after they leave atoms. This method is very complex and expensive to implement, while not examining tunneling directly.

An alternative method for studying tunnelling directly was introduced in the paper by Babushkin and his colleagues. The new method looks at the radiation released by electrons during the tunnelling process.

The method is very unusual from the point of view of normal intuition. Suppose you want to measure the flap of a butterfly's wings. You need a clock that works faster than the flap. If you try to use an ancient sun clock, which can measure hours, but not minutes and not seconds, what will happen? The period of light waves that we catch up to measure the attosecond time scales is 10 times larger than the attosecond time scales. But, as we showed, this is possible.

The attoclock was developed by Babushkin and his colleagues as a way to measure the light coming from electrons. The strong electric field leaving the atom had to vary in time and be circularly polarized for it to work as a clock.

The electric field rotates with time as a hand of a clock if the light is circularly polarized. With this, the response of the electron can be in the range of 1 to 12 Terahertz.

The researchers were able to see the dynamics of the terahertz radiation by measuring its polarization. The result was unexpected as the attosecond time scales differ by nine orders of magnitude.

The optical attoclock can be much more precise than the usual attoclock procedure because of the more precise measurement of the light polarization.

The researchers were able to measure something that had never been detected using the traditional attoclock method. In the future, they believe it could be used to collect time-resolved measurements in systems where electrons can't be detected.

Due to their high fabrication costs, attoclocks can only be produced in a few laboratories. The system created by Babushkin and his colleagues was built using less expensive components than the ones underpinning other realizations of the attoclock, which could lead to the collection of attoclock measurements in more institutes worldwide.

The attoclock could have many different applications. The traditional attoclock procedure does not work here. We believe that our new tool will help to gather a lot of interesting information, as the processes excited by strong optics fields are on the edge of the attosecond science.

More information: All-optical attoclock for imaging tunnelling wavepackets. Nature Physics(2022). DOI: 10.1038/s41567-022-01505-2.

There are attosecond and tunnelling delays in Helium. Science. There is a science.

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