̽��ֱ�� of Cambridge - KU Leuven

Colour-changing magnifying glass gives clear view of infrared light

sc604 — Thu, 02 Dec 2021 19:00:00 +0000

Detecting light beyond the visible red range of our eyes is hard to do, because infrared light carries so little energy compared to ambient heat at room temperature. This obscures infrared light unless specialised detectors are chilled to very low temperatures, which is both expensive and energy-intensive.

Now researchers led by the ̽��ֱ�� of Cambridge have demonstrated a new concept in detecting infrared light, showing how to convert it into visible light, which is easily detected.

In collaboration with colleagues from the UK, Spain and Belgium, the team used a single layer of molecules to absorb the mid-infrared light inside their vibrating chemical bonds. These shaking molecules can donate their energy to visible light that they encounter, ‘upconverting’ it to emissions closer to the blue end of the spectrum, which can then be detected by modern visible-light cameras.

̽��ֱ��results, reported in the journal Science, open up new low-cost ways to sense contaminants, track cancers, check gas mixtures, and remotely sense the outer universe.

̽��ֱ��challenge faced by the researchers was to make sure the quaking molecules met the visible light quickly enough. “This meant we had to trap light really tightly around the molecules, by squeezing it into crevices surrounded by gold,” said first author Angelos Xomalis from Cambridge’s Cavendish Laboratory.

̽��ֱ��researchers devised a way to sandwich single molecular layers between a mirror and tiny chunks of gold, only possible with ‘meta-materials’ that can twist and squeeze light into volumes a billion times smaller than a human hair.

“Trapping these different colours of light at the same time was hard, but we wanted to find a way that wouldn’t be expensive and could easily produce practical devices,” said co-author Dr Rohit Chikkaraddy from the Cavendish Laboratory, who devised the experiments based on his simulations of light in these building blocks.

“It’s like listening to slow-rippling earthquake waves by colliding them with a violin string to get a high whistle that’s easy to hear, and without breaking the violin,” said Professor Jeremy Baumberg of the NanoPhotonics Centre at Cambridge’s Cavendish Laboratory, who led the research.

̽��ֱ��researchers emphasise that while it is early days, there are many ways to optimise the performance of these inexpensive molecular detectors, which then can access rich information in this window of the spectrum.

From astronomical observations of galactic structures to sensing human hormones or early signs of invasive cancers, many technologies can benefit from this new detector advance.

̽��ֱ��research was conducted by a team from the ̽��ֱ�� of Cambridge, KU Leuven, ̽��ֱ�� College London (UCL), the Faraday Institution, and Universitat Politècnica de València.

̽��ֱ��research is funded as part of a UK Engineering and Physical Sciences Research Council (EPSRC) investment in the Cambridge NanoPhotonics Centre, as well as the European Research Council (ERC), Trinity College Cambridge and KU Leuven.

Jeremy Baumberg is a Fellow of Jesus College, Cambridge.

Reference:
Angelos Xomalis et al. ‘Detecting mid-infrared light by molecular frequency upconversion with dual-wavelength hybrid nanoantennas’, Science (2021). DOI: 10.1126/science.abk2593

By trapping light into tiny crevices of gold, researchers have coaxed molecules to convert invisible infrared into visible light, creating new low-cost detectors for sensing.

It’s like listening to slow-rippling earthquake waves by colliding them with a violin string to get a high whistle that’s easy to hear, and without breaking the violin

Jeremy Baumberg

NanoPhotonics Cambridge /Ermanno Miele, Jeremy Baumberg

Nano-antennas convert invisible infrared into visible light

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. Images, including our videos, are Copyright © ̽��ֱ�� of Cambridge and licensors/contributors as identified. All rights reserved. We make our image and video content available in a number of ways – as here, on our main website under its Terms and conditions, and on a range of channels including social media that permit your use and sharing of our content under their respective Terms.

Yes

Taming the multiverse: Stephen Hawking’s final theory about the big bang

sc604 — Wed, 02 May 2018 10:47:29 +0000

̽��ֱ��theory, which was submitted for publication before Hawking’s death earlier this year, is based on string theory and predicts the universe is finite and far simpler than many current theories about the big bang say.

Professor Hertog, whose work has been supported by the European Research Council, first announced the new theory at a conference at the ̽��ֱ�� of Cambridge in July of last year, organised on the occasion of Professor Hawking’s 75^th birthday.

Modern theories of the big bang predict that our local universe came into existence with a brief burst of inflation – in other words, a tiny fraction of a second after the big bang itself, the universe expanded at an exponential rate. It is widely believed, however, that once inflation starts, there are regions where it never stops. It is thought that quantum effects can keep inflation going forever in some regions of the universe so that globally, inflation is eternal. ̽��ֱ��observable part of our universe would then be just a hospitable pocket universe, a region in which inflation has ended and stars and galaxies formed.

“ ̽��ֱ��usual theory of eternal inflation predicts that globally our universe is like an infinite fractal, with a mosaic of different pocket universes, separated by an inflating ocean,” said Hawking in an interview last autumn. “ ̽��ֱ��local laws of physics and chemistry can differ from one pocket universe to another, which together would form a multiverse. But I have never been a fan of the multiverse. If the scale of different universes in the multiverse is large or infinite the theory can’t be tested. ”

In their new paper, Hawking and Hertog say this account of eternal inflation as a theory of the big bang is wrong. “ ̽��ֱ��problem with the usual account of eternal inflation is that it assumes an existing background universe that evolves according to Einstein’s theory of general relativity and treats the quantum effects as small fluctuations around this,” said Hertog. “However, the dynamics of eternal inflation wipes out the separation between classical and quantum physics. As a consequence, Einstein’s theory breaks down in eternal inflation.”

“We predict that our universe, on the largest scales, is reasonably smooth and globally finite. So it is not a fractal structure,” said Hawking.

̽��ֱ��theory of eternal inflation that Hawking and Hertog put forward is based on string theory: a branch of theoretical physics that attempts to reconcile gravity and general relativity with quantum physics, in part by describing the fundamental constituents of the universe as tiny vibrating strings. Their approach uses the string theory concept of holography, which postulates that the universe is a large and complex hologram: physical reality in certain 3D spaces can be mathematically reduced to 2D projections on a surface.

Hawking and Hertog developed a variation of this concept of holography to project out the time dimension in eternal inflation. This enabled them to describe eternal inflation without having to rely on Einstein’ theory. In the new theory, eternal inflation is reduced to a timeless state defined on a spatial surface at the beginning of time.

“When we trace the evolution of our universe backwards in time, at some point we arrive at the threshold of eternal inflation, where our familiar notion of time ceases to have any meaning,” said Hertog.

Hawking’s earlier ‘no boundary theory’ predicted that if you go back in time to the beginning of the universe, the universe shrinks and closes off like a sphere, but this new theory represents a step away from the earlier work. “Now we’re saying that there is a boundary in our past,” said Hertog.

Hertog and Hawking used their new theory to derive more reliable predictions about the global structure of the universe. They predicted the universe that emerges from eternal inflation on the past boundary is finite and far simpler than the infinite fractal structure predicted by the old theory of eternal inflation.

Their results, if confirmed by further work, would have far-reaching implications for the multiverse paradigm. “We are not down to a single, unique universe, but our findings imply a significant reduction of the multiverse, to a much smaller range of possible universes,” said Hawking.

This makes the theory more predictive and testable.

Hertog now plans to study the implications of the new theory on smaller scales that are within reach of our space telescopes. He believes that primordial gravitational waves – ripples in spacetime – generated at the exit from eternal inflation constitute the most promising “smoking gun” to test the model. ̽��ֱ��expansion of our universe since the beginning means such gravitational waves would have very long wavelengths, outside the range of the current LIGO detectors. But they might be heard by the planned European space-based gravitational wave observatory, LISA, or seen in future experiments measuring the cosmic microwave background.

Reference:
S.W. Hawking and Thomas Hertog. ‘A Smooth Exit from Eternal Inflation?’’ Journal of High-Energy Physics (2018). DOI: 10.1007/JHEP04(2018)147

Professor Stephen Hawking’s final theory on the origin of the universe, which he worked on in collaboration with Professor Thomas Hertog from KU Leuven, has been published in the Journal of High Energy Physics.

We are not down to a single, unique universe, but our findings imply a significant reduction of the multiverse, to a much smaller range of possible universes.

Stephen Hawking

Andre Pattenden

Stephen Hawking

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. For image use please see separate credits above.

Yes