0.0000000000000000005 seconds – physicists generate one of the shortest signals ever produced by humans

Scientists from the University of Konstanz have developed a method that uses femtosecond flashes of light to generate electronic pulses with a duration of about five attoseconds. This achievement, which provides higher temporal resolution than light waves, paves the way for observing ultrafast phenomena, such as nuclear reactions.

Physicists from the University of Konstanz have generated one of the shortest signals ever produced by humans.

Molecular or solid-state processes in nature can sometimes occur on time frames as short as femtoseconds (quadrillionths of a second) or attoseconds (quintillionths of a second). Nuclear reactions are faster. Now, Maxim Tsarev, Johannes Thurner and Peter Baum, scientists from the University of Konstanz, use a new experimental set-up to achieve signals with a duration of attoseconds, i.e. billionths of a nanosecond, opening new horizons in the field of ultrafast phenomena.

Not even light waves can achieve such time resolution because a single oscillation takes too long to do so. Electrons provide a cure here, because they allow much higher temporal resolution. In their experimental setup, the Konstanz researchers used pairs of femtosecond light flashes from a laser to generate extremely short electron pulses in a free-space beam. The results are published in the journal Nature physics.

How did scientists go about this?

Similar to water waves, light waves can also overlap to form the crests and troughs of stationary or traveling waves. Physicists chose incidence angles and frequencies so that the electrons involved in propagation, which fly through a vacuum at half the speed of light, overlap the crests and troughs of light waves at exactly the same speed.

What is known as the deep driving force pushes the electrons towards the trough of the next wave. Thus, after a short interaction, a series of electron pulses is generated that is very short in time – especially in the middle of the pulse train, where the electric fields are very strong.

For a short time, the duration of electron pulses is only about five attoseconds. In order to understand this process, the researchers measured the speed distribution of the electrons that remained after compression. “Instead of a very uniform speed of the output pulses, you see a very broad distribution that results from the strong deceleration or acceleration of some of the electrons during compression,” explains physicist Johannes Thurner. “But not only that: the distribution is not smooth. Instead, it consists of thousands of speed steps, since only an integer number of pairs of light particles can interact with electrons at a time.

Importance of research

The scientist says that quantum mechanics is a time superposition (overlap) of electrons with themselves, after experiencing the same acceleration at different times. This effect is relevant to quantum mechanics experiments, for example, the interaction of electrons and light.

It is also striking: Plane electromagnetic waves, such as a light beam, cannot normally cause permanent changes in the speed of electrons in a vacuum, because the total energy and total momentum of a massive electron and a light particle have zero mass (Photon) cannot be saved. However, the presence of two photons simultaneously in a wave traveling at a speed slower than the speed of light solves this problem (the Kapitza-Dirac effect).

For Peter Baum, professor of physics and head of the Light and Matter Group at the University of Konstanz, these results are still clearly basic research, but he underscores the great potential for future research: “If a substance collides with two of our short pulses and at variable time intervals, the first pulse can trigger To change the second pulse can be used for surveillance – similar to a camera flash.

From his point of view, the great advantage is that there is no matter involved in the empirical principle, and everything occurs in free space. In principle, lasers of any power could be used in the future to obtain stronger pressure. “Our new photon pressure allows us to move into new dimensions of time and perhaps even image nuclear reactions,” Baum says.

Reference: “Nonlinear optical quantum control of free electronic matter waves” by Maxim Tsarev, Johannes W. Thurner and Peter Baum, 12 June 2023, Nature physics.
doi: 10.1038/s41567-023-02092-6

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