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.
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.
The research is detailed in the paper “Generation of Even and Odd High
Harmonics in Resonant Metasurfaces Using Single and Multiple Ultra-Intense
Laser Pulses,” published on July 7, 2021, in Nature Communications. Maxim
Shcherbakov, who conducted the research as a Cornell postdoctoral associate
before becoming an assistant professor at the University of California,
Irvine, is the lead author.
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 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.
Reference:
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 and Gennady Shvets, 7 July 2021, Nature
Communications.