Nav: Home

Scientists find holes in light by tying it in knots

August 01, 2018

A research collaboration including theoretical physicists from the University of Bristol and Birmingham has found a new way of evaluating how light flows through space - by tying knots in it.

Laser light may appear to be a single, tightly focused beam. In fact, it's an electromagnetic field, vibrating in an ellipse shape at each point in space. This multidirectional light is said to be 'polarised'.

The effect can be seen with polarised sunglasses, which only allow one direction of light to penetrate. By holding them up to the sky and rotating them, viewers will see darker and brighter patches as light flowing in different directions appears and disappears.

Now, scientists have been able to use holographic technology to twist a polarised laser beam into knots.

Professor Mark Dennis, from the University of Bristol's School of Physics and University of Birmingham's School of Physics and Astronomy, led the theoretical part of the research.

He said: "We are all familiar with tying knots in tangible substances such as shoelaces or ribbon. A branch of mathematics called 'knot theory' can be used to analyse such knots by counting their loops and crossings.

"With light, however, things get a little more complex. It isn't just a single thread-like beam being knotted, but the whole of the space or 'field' in which it moves.

"From a maths point of view, it isn't the knot that's interesting, it's the space around it. The geometric and spatial properties of the field are known as its topology."

In order to analyse the topology of knotted light fields, researchers from universities in Bristol, Birmingham, Ottowa and Rochester used polarised light beams to create structures known as 'polarisation singularities'.

Discovered by Professor John Nye in Bristol over 35 years ago, polarisation singularities occur at points where the polarisation ellipse is circular, with other polarisations wrapping around them. In 3 dimensions, these singularities occur along lines, in this case creating knots.

The team were able to create knots of much greater complexity than previously possible in light and analysed them in fine detail.

Professor Dennis added: "One of the purposes of topology is to talk about showing data in terms of lines and surfaces. The real-world surfaces have a lot more holes than the maths predicted."
-end-
The work, which was funded by a Leverhulme Trust Research Project Grant, is an important step forward in the study of optics and polarisation, and, say researchers, could lead to the creation of new devices which process information through customised complex light structures.

University of Bristol

Related Research Articles:

More Research News and Research Current Events

Trending Science News

Current Coronavirus (COVID-19) News

Top Science Podcasts

We have hand picked the top science podcasts of 2020.
Now Playing: TED Radio Hour

Climate Mindset
In the past few months, human beings have come together to fight a global threat. This hour, TED speakers explore how our response can be the catalyst to fight another global crisis: climate change. Guests include political strategist Tom Rivett-Carnac, diplomat Christiana Figueres, climate justice activist Xiye Bastida, and writer, illustrator, and artist Oliver Jeffers.
Now Playing: Science for the People

#562 Superbug to Bedside
By now we're all good and scared about antibiotic resistance, one of the many things coming to get us all. But there's good news, sort of. News antibiotics are coming out! How do they get tested? What does that kind of a trial look like and how does it happen? Host Bethany Brookeshire talks with Matt McCarthy, author of "Superbugs: The Race to Stop an Epidemic", about the ins and outs of testing a new antibiotic in the hospital.
Now Playing: Radiolab

Speedy Beet
There are few musical moments more well-worn than the first four notes of Beethoven's Fifth Symphony. But in this short, we find out that Beethoven might have made a last-ditch effort to keep his music from ever feeling familiar, to keep pushing his listeners to a kind of psychological limit. Big thanks to our Brooklyn Philharmonic musicians: Deborah Buck and Suzy Perelman on violin, Arash Amini on cello, and Ah Ling Neu on viola. And check out The First Four Notes, Matthew Guerrieri's book on Beethoven's Fifth. Support Radiolab today at Radiolab.org/donate.