Smuggling light through opaque materials
Newly proven physics opens chalcogenide glasses to applications at
visible and ultraviolet wavelengths

Date:
October 5, 2021
Source:
Duke University
Summary:
Electrical engineers have discovered that changing the physical
shape of a class of materials commonly used in electronics can
extend their use into the visible and ultraviolet parts of the
electromagnetic spectrum.

Already commercially used in detectors, lenses and optical fibers,
chalcogenide glasses may now find a home in applications such as
underwater communications, environmental monitoring and biological
imaging.



FULL STORY ========================================================================== Electrical engineers at Duke University have discovered that changing the physical shape of a class of materials commonly used in electronics and
near- and mid-infrared photonics -- chalcogenide glasses -- can extend
their use into the visible and ultraviolet parts of electromagnetic
spectrum. Already commercially used in detectors, lenses and optical
fibers, chalcogenide glasses may now find a home in applications such
as underwater communications, environmental monitoring and biological
imaging.


==========================================================================
The results appear online on October 5 in the journal Nature
Communications.

As the name implies, chalcogenide glasses contain one or more chalcogens
- - chemical elements such as sulfur, selenium and tellurium. But
there's one member of the family they leave out: oxygen. Their material properties make them a strong choice for advanced electronic applications
such as optical switching, ultra-small direct laser writing (think
tiny rewritable CDs) and molecular fingerprinting. But because they
strongly absorb wavelengths of light in the visible and ultraviolet
parts of electromagnetic spectrum, chalcogenide glasses have long
been constrained to the near- and mid-infrared with respect to their applications in photonics.

"Chalcogenides have been used in the near- and mid-IR for a long time,
but they've always had this fundamental limitation of being lossy at
visible and UV wavelengths," said Natalia Litchinitser, professor of
electrical and computer engineering at Duke. "But recent research
into how nanostructures affect the way these materials respond to
light indicated that there might be a way around these limitations."
In recent theoretical research into the properties of gallium arsenide
(GaAs), a semiconductor commonly used in electronics, Litchinitser' s collaborators, Michael Scalora of the US Army CCDC Aviation and Missile
Center and Maria Vincenti of the University of Brescia predicted that nanostructured GaAs might respond to light differently than its bulk or
even thin film counterparts.

Because of the way that high intensity optical pulses interact with the nanostructured material, very thin wires of the material lined up next
to one another might create higher-order harmonic frequencies (shorter wavelengths) that could travel through them.

Imagine a guitar string that is tuned to resonate at 256 Hertz --
otherwise known as middle C. The researchers were proposing that if
fabricated just right, this string when plucked might also vibrate at frequencies one or two octaves higher in small amounts.



========================================================================== Litchinitser and her PhD student Jiannan Gao decided to see if the same
might be true for chalcogenide glasses. To test the theory, colleagues
at the Naval Research Laboratory deposited a 300-nanometer-thin film of
arsenic trisulfide onto a glass substrate that was next nanostructured
using electron beam lithography and reactive ion etching to produce
arsenic trisulfide nanowires of 430 nanometers wide and 625 nanometers
apart.

Even though arsenic trisulfide completely absorbs light above 600 THz - - roughly the color of cyan -- the researchers discovered their nanowires
were transmitting tiny signals at 846 THz, which is squarely in the
ultraviolet spectrum.

"We found that illuminating a metasurface made of judiciously designed nanowires with near-infrared light resulted in generation and transmission
of both the original frequency and its third harmonic, which was very unexpected because the third harmonic falls into the range where the
material should be absorbing it," Litchinitser said.

This counterintuitive result is due to the effect of nonlinear
third harmonic generation and its "phase locking" with the original
frequency. "The initial pulse traps the third harmonic and sort of tricks
the material into letting them both pass through without any absorption," Litchinitser said.

Moving forward, Litchinitser and her colleagues are working to see if
they can engineer different shapes of chalcogenides that can carry these harmonic signals even better than the initial nanostrips. For example,
they believe that pairs of long, thin, Lego-like blocks spaced certain distances apart might create a stronger signal at both third and second harmonic frequencies. They also predict that stacking multiple layers
of these metasurfaces on top of one another might enhance the effect.

If successful, the approach could unlock a wide range of visible
and ultraviolet applications for popular electronic material and
mid-infrared photonic materials that have long been shut out of these
higher frequencies.

This work was supported by Office of Naval Research (N00014-19-1-2163,
N00014- 20-1-2558), the Army Research Laboratory Cooperative Agreement (W911NF-20-2- 0078), and the National Science Foundation (ECCS-1846766, OMA-1936276).

========================================================================== Story Source: Materials provided by Duke_University. Original written
by Ken Kingery. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Jiannan Gao, Maria Antonietta Vincenti, Jesse Frantz, Anthony
Clabeau,
Xingdu Qiao, Liang Feng, Michael Scalora, Natalia
M. Litchinitser. Near- infrared to ultra-violet frequency conversion
in chalcogenide metasurfaces. Nature Communications, 2021; 12 (1)
DOI: 10.1038/s41467- 021-26094-1 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/10/211005124739.htm

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