Scientists develop new, cheap way to make radially polarised white light

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Scientists from the UK have developed a new, low-cost method for creating radially polarised white light, which could lead to scientific advances in astronomy and microscopy. 

The team from the University of Glasgow’s School of Physics and Astronomy in Scotland discovered the new technique for producing radially polarised beams by using broadband white light rather than single frequency beams, and reflecting the light from a glass cone. 

It was found that if white light with a uniform polarisation across the whole beam is reflected back from a small glass cone, the light becomes an optical vortex – for example with polarisation always pointing to the centre.  Such light can be focused on a much smaller scale than was previously thought possible. 

Until now, scientists created radially polarised beams using nano-fabricated devices, which are extremely expensive and tend to use single frequency light.  

A cheaper way of producing beams using broadband light could be useful in microscopy, allowing scientists to record images with a much better resolution, and also in astronomy, where so-called vortex coronagraphs can be used to see faint objects from light years away that are normally obscured by near, very bright stars. 

Dr Neal Radwell, the lead author of the paper published in Nature Communications, said: ‘Scientists can make these kinds of beams already but we have found the first way of making radial polarisation using white light – light that contains all different colours – rather than lasers and light of a very particular frequency.' 

‘What we have proved is not that you can focus these beams better, that has been shown before, but we have found a new way to make those beams.’ 

Dr Sonja Franke-Arnold, who devised the glass cone technology, added: ‘This doesn’t allow you to do things you couldn’t do before but it does give us a new way to create these beams, which is potentially cheaper and it is broadband as it works with white light. That is why it has potential application not only in microscopy but also astronomy where researchers are interested in star light across the whole visual spectrum.’  

As yet the commercial uses of these radially polarised beams from glass cones are still relatively unclear, but Dr Radwell explained: ‘It wasn’t our intent to realise commercial applications during this research, it was purely for scientific applications and inspired by scientific curiosity.’

Further information 

University of Glasgow’s School of Physics and Astronomy