FEATURE SCIENTIFIC LASERS
Attosecond
In the hands of the few, attosecond pulses have already provided glimpses of fundamental ultrafast processes. Benjamin Skuse asks: what might be achieved if access were broadened to the wider world?
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n the attoworld, ‘in the blink of an eye’ doesn’t cut it as a description for just how rapid processes are. If an attosecond were stretched out to a second, a blink would take almost the entire age of the Universe. It’s a billionth of a billionth of a second, a nano nanosecond. What is the purpose of detecting such
unfathomably fast processes? It just so happens that the attosecond is the natural timescale of electron motion in atoms,
20 Electro Optics November 2022
science for all
molecules and solids. “We’re talking about not only very short timescales, but also very small spatial scales,” says Michael Chini , from the University of Central Florida, USA. “And what that means is that attosecond science is fundamentally a science that involves quantum mechanics.” Directly measuring quantum processes is now possible. Attosecond science may even one day provide the means of controlling them. As a result, attosecond science is widely
regarded as having huge potential to advance fundamental research, not only in quantum physics but also in biology, chemistry, medicine and others. More generally, the scientific community is in agreement that attosecond tools open up new possibilities in various critical sectors. Already, researchers have probed the fast
interactions of electrons in, for example, organic photovoltaic materials, which hold promise as new solar cell materials or catalysts but are currently either unstable or inefficient. A detailed understanding of the charge transfer pathway could help optimise such next-generation photosensitive elements. Another promising application is
electronics. In today’s electronic circuits, electrons are driven by microwave voltages to switch the current on and off in a fraction of a nanosecond. Theoretically, the fastest switching time possible is the time it takes an electron to travel between neighbouring atoms, a process occurring at the attosecond scale. For this reason, smaller structures allowing faster switching speeds are being explored with the overarching aim of realising petahertz electronics, in which the direction of electric current can be changed several trillion times per second; roughly 100,000 times faster than permitted by today’s electronics.
Towards attosecond science What has made such feats enter the realm of possibility has been advances in photonics. From the 1960s onwards, laser pulse durations shrank from roughly microsecond durations to nanoseconds and, by the mid- 1980s, the several femtosecond regime. There, progress stagnated for a decade and a half. But in the meantime, the foundations for attosecond science were being laid. Among numerous advances, chirped pulse amplification (CPA) stands out as being
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