This July 21, 2021 news item on Nanowerk is all about laser pulses and tiny timescales.
Cornell researchers have developed nanostructures that enable record-breaking conversion of laser pulses into high-harmonic generation, paving the way for new scientific tools for high-resolution imaging and studying physical processes that occur at the scale of an attosecond – one quintillionth of a second [emphasis mine].
High-harmonic generation has long been used to merge photons from a pulsing laser into one, ultrashort photon with much higher energy, producing extreme ultraviolet light and X-rays used for a variety of scientific purposes. Traditionally, gases have been used as sources of harmonics, but a research team led by Gennady Shvets, professor of applied and engineering physics in the College of Engineering, has shown that engineered nanostructures have a bright future for this application.
A July 21, 2021 Cornell University news release by Syl Kacapyr (also on EurekAlert), which originated the news item, provides more detail about the nanostructures,
The nanostructures created by the team make up an ultrathin resonant gallium-phosphide metasurface that overcomes many of the usual problems associated with high-harmonic generation in gases and other solids. The gallium-phosphide material permits harmonics of all orders without reabsorbing them, and the specialized structure can interact with the laser pulse’s entire light spectrum.
“Achieving this required engineering of the metasurface’s structure using full-wave simulations,” Shcherbakov [Maxim Shcherbakov] said. “We carefully selected the parameters of the gallium-phosphide particles to fulfill this condition, and then it took a custom nanofabrication flow to bring it to light.”
The result is nanostructures capable of generating both even and odd harmonics – a limitation of most other harmonic materials – covering a wide range of photon energies between 1.3 and 3 electron volts. The record-breaking conversion efficiency enables scientists to observe molecular and electronic dynamics within a material with just one laser shot, helping to preserve samples that may otherwise be degraded by multiple high-powered shots.
The study is the first to observe high-harmonic generated radiation from a single laser pulse, which allowed the metasurface to withstand high powers – five to 10 times higher than previously shown in other metasurfaces.
“It opens up new opportunities to study matter at ultrahigh fields, a regime not readily accessible before,” Shcherbakov said. “With our method, we envision that people can study materials beyond metasurfaces, including but not limited to crystals, 2D materials, single atoms, artificial atomic lattices and other quantum systems.”
Now that the research team has demonstrated the advantages of using nanostructures for high-harmonic generation, it hopes to improve high-harmonic devices and facilities by stacking the nanostructures together to replace a solid-state source, such as crystals.
Here’s a link to and a citation for the paper,
Generation of even and odd high harmonics in resonant metasurfaces using single and multiple ultra-intense laser pulses by Maxim R. Shcherbakov, Haizhong Zhang, Michael Tripepi, Giovanni Sartorello, Noah Talisa, Abdallah AlShafey, Zhiyuan Fan, Justin Twardowski, Leonid A. Krivitsky, Arseniy I. Kuznetsov, Enam Chowdhury & Gennady Shvets. Nature Communications volume 12, Article number: 4185 DOI: https://doi.org/10.1038/s41467-021-24450-9 Published: 07 July 2021
This paper is open access.