Scientists make a new type of optical device using alumina
Date:
January 27, 2022
Source:
Kavli Institute for the Physics and Mathematics of the Universe
Summary:
Researchers have developed an alumina short-wavelength absorber
patterned with moth eye-like structures. These new anti-reflective
structures will improve the performance of telescopes studying
radiation from the Big Bang.
FULL STORY ========================================================================== Scientists from the Kavli Institute for the Physics and Mathematics of the Universe and the University of Minnesota, Tomotake Matsumura and Shaul
Hanany, and their collaborators have made a new type of optical element
that will improve the performance of telescopes studying radiation from
the Big Bang.
==========================================================================
The cosmic microwave background (CMB) is a relic radiation remnant
from the big bang. It reaches our telescopes after traveling 14 billion
years since the birth of the Universe. Studying the properties of this radiation, scientists infer the physics of the big bang, how clusters of galaxies form, and the matter and energy content in the Universe. Four
Nobel prizes have been awarded for past studies of the CMB.
To study the CMB, telescopes must be tuned to wavelengths in which it is
most intense, about 1-3 mm, and they must separate out shorter wavelength radiation that the atmosphere and Milky Way emit. Among the most effective optical elements that absorbs the short wavelength radiation but lets
the CMB pass through is alumina, a material made of aluminum and oxygen
and that is second in hardness only to diamond. One challenge with using alumina is that it also reflects almost 50% of the radiation impinging
on it. Matsumura and Hanany have now come up with a new way to fabricate anti-reflective structures that reduce reflections fifty-fold.
The researchers partnered with Mark Devlin and Simon Dicker, colleagues at
the University of Pennsylvania who are operating the MUSTANG2 instrument,
which is coupled to the Green Bank Telescope in Virginia. Hanany and
Matsumura provided the MUSTANG2 team with an alumina short-wavelength
absorber that has the new anti-reflective structures. The MUSTANG2
instrument is now conducting sky observations with the new technology, demonstrating for the first time its success.
The researchers patterned the alumina with small pyramidal structures,
which are about one millimeter tall (0.04 inch) and repeat across
the 30 cm (one foot) diameter with a periodicity of just less than one millimeter. It has long been known that incorporating such structures on
the surfaces of materials reduces reflections. With the small pyramids,
light enters and is leaving the material more gradually, leading to much
lower reflection. Matsumura and Hanany's innovation is in the way they patterned the alumina, which is too hard to be machined with standard
tools. They used ultra-short pulsed laser, with pulses few trillionths
of a second long and reaching 100 megawatts each, to ablate the material
away and to shape the surface relief to its optimal anti- reflective
shape. Within about four days the laser process produced 320,000 pyramids
on both sides of the alumina disc. The researchers measured the properties
of the alumina sample and showed that it reflects less than 1% of the
incident radiation. This is the first time such an optical element has
been fabricated and coupled to an operating instrument, and it is the
largest sample of alumina to have been laser-ablated.
This innovation will lead to more efficient instruments peering back in
time and revealing the physical process at the Big Bang and throughout
the evolution of the universe.
========================================================================== Story Source: Materials provided by Kavli_Institute_for_the_Physics_and_Mathematics_of_the Universe. Note:
Content may be edited for style and length.
========================================================================== Journal Reference:
1. Ryota Takaku, Qi Wen, Scott Cray, Mark Devlin, Simon Dicker, Shaul
Hanany, Takashi Hasebe, Teruhito Iida, Nobuhiko Katayama, Kuniaki
Konishi, Makoto Kuwata-Gonokami, Tomtoake Matsumura, Norikatsu Mio,
Haruyuki Sakurai, Yuki Sakurai, Ryohei Yamada, Junji Yumoto. A
Large Diameter Millimeter-Wave Low-Pass Filter Made of Alumina
with Laser Ablated Anti-Reflection Coating. Optics Express, 2021;
DOI: 10.1364/ OE.444848 ==========================================================================
Link to news story:
https://www.sciencedaily.com/releases/2022/01/220127103944.htm
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