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Lenses produced for less than a penny

Australian scientists have developed a way to create inexpensive lenses that cost less than a penny to produce. The new approach has allowed the team from the Australian National University (ANU) to build a 3D printed lens attachment that turns a smartphone camera into a dermascope, a tool to diagnose skin diseases like melanoma, which could be commercially available within the next few months. The work, published in The Optical Society’s (OSA) journal Biomedical Optics Express, could also be used in the future for applications such as scientific research in the lab, devices to detect diseases in the field, and optical lenses and microscopes for education in classrooms. With the new method, the researchers harvest solid lenses of varying focal lengths by hanging and curing droplets of a gel-like material, a simple and inexpensive approach that avoids costly or complicated machinery.

‘What I did was to

systematically fine-tune the curvature that’s formed by a simple droplet with the help of gravity, and without any moulds,’ said Dr Steve Lee from the Research School of Engineering at Australian National University (ANU), who invented the technique.

The process requires an

oven, a microscope glass slide and a common, gel- like silicone polymer called polydimethylsiloxane (PDMS). First, a drop of PDMS is added onto the slide. Then, it is heated at 70°C to harden it, creating a base.

Another drop of PDMS is added onto the base and turned over, and gravity pulls the new droplet down into a parabolic shape. The droplet is then heated again to solidify the lens. More drops can be added to hone the shape of the lens that also greatly increases the imaging quality of the lens. ‘It’s a low-cost and easy lens- making recipe,’ said Lee.


Proving the impossible: experiment devised to convert light into matter


practical experiment to prove Breit and Wheeler’s theory that it would be possible to convert light into matter

has been devised by Imperial College London physicists after an 80-year wait. While the theory is accepted to be true, it was initially said to be impossible to prove under laboratory conditions. However, in just one day, three physicists have managed to calculate a way of physically proving the hypothesis, which has been published in the journal, Nature Photonics.

By colliding two photons together, the theory

states, an electron and a positron can be created. The method suggests a photon-photon collider and would open up an entire new type of experimental high-energy physics.

created would then be detectable as they exited the hohlraum.

Lead researcher Oliver Pike said: ‘Although the theory is conceptually simple, it has been very difficult to verify experimentally. We were able to develop the idea for the collider very quickly, but the experimental design we propose can be carried out with relative ease and with existing technology.’

The scientists suggest colliding high-energy photons within a small gold container called a hohlraum. A high-energy beam is produced by accelerating electrons to close to the speed of light and firing them into a slab of gold. This would create a beam of photons which, the university said, is a billion times more energetic than visible light. A high-energy laser is used to create a thermal radiation field, which contains light similar to that emitted by stars, by directing the beam at the inside of the hohlraum.

‘ By colliding two photons, the theory states, an electron and a positron can be created’

The scientists had been investigating problems with fusion energy when they realised what they were working on could be applied to the Breit-Wheeler theory. The breakthrough was achieved in collaboration with a fellow theoretical physicist from the Max Planck Institute for Nuclear Physics, who happened to be visiting Imperial. Pike continued: ‘Within a few

hours of looking for applications of hohlraums outside their traditional role in fusion energy research, we were astonished to find they provided the perfect conditions for creating a photon collider. The race to carry out and complete the experiment is on!’ Demonstrating the Breit-Wheeler theory would

The beam from the gold slab is then directed through the centre of the can where the photons then collide with the photons from the thermal radiation field.

The electrons and positrons which are

provide the final jigsaw piece of a physics puzzle which describes the simplest ways in which light and matter interact. The six other pieces in that puzzle, including Dirac’s 1930 theory on the annihilation of electrons and positrons and Einstein’s 1905 theory on the photoelectric effect, are all associated with Nobel Prize- winning research.

World’s first photonics crystal laser created

A next-generation semiconductor laser light source has been developed by Hamamatsu Photonics and Kyoto University’s Photonics and Electronics Science and Engineering Center in Japan. The watt-level photonics crystal laser, described in journal Nature Photonics, was shown to operate continuously at room temperature, generating a power output of 1.5W while maintaining a beam spread of less than three degrees. The team of researchers also demonstrated the utility of the laser’s high brightness and

high output by showing how it can burn through a substance through direct, lens-less irradiation. These results are a significant milestone for laser-based manufacturing in Japan, as they lay the groundwork for the future adoption of this new type of laser for laser excitation, wavelength conversion, biotechnology, analytical chemistry, and other applications. Results have already been published in the electronic version of Nature Photonics, and will appear in the May issue of the publication.

@electrooptics |

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