Photon frequency doubler is controlled by light

21 Jan 2020

Doubling up: Georgia Tech researchers Kyu-Tae Lee (left) and Mohammad Taghinejad demonstrate frequency doubling on a slab of titanium dioxide using a red laser to create nonlinear effects with tiny triangles of gold. The blue beam shows the frequency-doubled light and the green beam controls the hot-electron migration. (Courtesy: Rob Felt/Georgia Tech)

A way of using light to convert a normal optical material into a frequency doubler has been developed by Mohammad Taghinejad and colleagues at the Georgia Institute of Technology. The technique could have a range of applications from creating all-optical information-processing devices to studying quantum-mechanical tunnelling.

Frequency doubling is an optical effect that occurs in spatially asymmetrical materials that have a second-order nonlinear susceptibility. Two photons with the same frequency can interact with the material and combine to form a single photon with twice the frequency of the original photons. While most crystalline materials do not have the appropriate asymmetry in the bulk, frequency doubling can occur at surfaces and interfaces. However, relying on these very thin regions is not ideal for creating practical devices.

Artificial intelligence reveals how light flows around nanoparticles

23 Jan 2020

Making connections: artificial intelligence has been used to predict how light flows around nanoparticles. (Courtesy: University of Southampton)

Artificial intelligence has been used to quickly and accurately model the 3D flow of light around arbitrarily shaped nanoparticles. Peter Wiecha and Otto Muskens at the University of Southampton in the UK demonstrated the modelling approach using a neural network that required just a single training procedure. Their technique could be used to design a wide range of optical devices that control the paths taken by light.

When light interacts with nanostructures that are smaller in size than the wavelength of the light, the result can be very different from how light interacts with larger structures and continuous media. The field of nanophotonics seeks to exploit this by designing nanoparticles with particular shapes and compositions with the aim of manipulating light in specific ways.

Forbidden nuclear transition sheds light on how some stars die

Forbidden nuclear transition sheds light on how some stars die

23 Jan 2020

Exploded star: the crab nebula is believed to have been created by the explosion of an intermediate-mass star. (Courtesy: NASA/ESA/ J Hester and A Loll, Arizona State University)

Intermediate-mass stars expire via thermonuclear explosions, rather than gravitational collapse, according to experiments and calculations done by an international team of astrophysicists led by Oliver Kirsebom at Dalhousie University in Canada. By measuring the rate of a “forbidden” nuclear decay that transforms fluorine-20 into neon-20, they were able to work out the rate at which neon-20 in a star will capture electrons in a stellar environment. This rate was much higher than previously thought, leading the team to conclude that such stars are more likely to expire in thermonuclear explosions.

ΤΑ ΚΟΥΝΟΥΠΙΑ

ΤΑ ΚΟΥΝΟΥΠΙΑ

Ο βιολογικός κύκλος του κουνουπιού αποτελείται από το αβγό, τα προνυμφικά στάδια (προνύμφη), τη νύμφη και τέλος το ακμαίο. Εκτός από το τελευταίο στάδιο (ακμαίο-το γνωστό ενοχλητικό κουνούπι που μας τσιμπά) όλα τα άλλα διαβιούν στο νερό.

Η διάρκεια του βιολογικού κύκλου των κουνουπιών εξαρτάται κυρίως από τη θερμοκρασία. Η διάρκεια της ζωής των ενηλίκων κουνουπιών (ακμαίων) εξαρτάται συνήθως από διάφορους παράγοντες όπως πχ θερμοκρασία, υγρασία, το φύλο του κουνουπιού και την εποχή του χρόνου. Τα αρσενικά ακμαία ζουν για περίπου μία εβδομάδα ενώ τα θηλυκά ζουν περισσότερο και ανάλογα με τους παραπάνω παράγοντες το διάστημα αυτό μπορεί να φτάσει έως και ένα μήνα. Τα κουνούπια, εκτός της όχλησης που προκαλούν, είναι οι φορείς αρκετών ασθενειών για τον άνθρωπο όπως ελονοσία (malaria), Δάγκειος αιμορραγικός πυρετός (dengue hemorrhagic fever), κίτρινος πυρετός (Yellow fever virus), τσικουνγκούνια (chikungunya) και ο ιός του Δυτικού Νείλου (West Nile virus). 

Ancient rings surrounding the Sun could have divided the solar system

16 Jan 2020

Stellar rings: an infrared image of rings around a star that was taken by ALMA. (Courtesy: ALMA/ESO/NAOJ/NRAO)

The clear divide between the inner and outer solar system is the legacy of a ring structure that existed a very long time ago in the planet-forming disc that surrounded the Sun. That is the conclusion of Ramon Brasser at Tokyo Institute of Technology and Stephen Mojzsis at the University of Colorado Boulder, who have combined computer simulations of Jupiter’s formation with observations of the discs surrounding young stars.

The solar system is clearly divided between the inner rocky planets and asteroids, and the outer gas giants – with the border between the two regions lying between Jupiter and the asteroid belt. This difference can be quantified in terms of carbon – with the element being much more abundant in the outer part of the solar system than it is in the inner rocky planets and asteroids. The difference is so stark that astronomers now widely believe that material in the newly-formed Sun’s planet-forming circumstellar disc was similarly divided in terms of its composition.

For some reason, carbon-rich material from the outer solar system has been prevented from migrating into the inner solar system. One explanation for this barrier is that it arose during formation of Jupiter. As the gas giant gathered mass, the theory proposes, it prevented carbon-rich dust and sub-metre “pebbles” from reaching the inner solar system.

‘Physical cryptography’ uses neutrons to compare nuclear warheads

26 Sep 2016 Hamish Johnston

No knowledge: the weapons-verification-technique set-up

A new technique for comparing physical objects – while keeping the composition of the objects secret – has been demonstrated by physicists in the US and Italy. Based on a scheme for cryptography, the method involves comparing how radiation is transmitted through two targets and could be used to verify the presence of nuclear weapons in warheads.

Future agreements on the control of nuclear weapons could require that all nuclear warheads be accounted for, including those in storage. This would rely on inspectors being able to tell a real nuclear warhead apart from a fake one. This is important because it would prevent a country from secretly stashing away some of its declared warheads and replacing them with fakes.

Lithium-6 enriched semiconductor is efficient detector of thermal neutrons

Lithium-6 enriched semiconductor is efficient 

detector of thermal neutrons15 Jan 2020 Hamish Johnston

Compact and efficient: prototype of a working, pocket-sized neutron detector made with semiconductor rich in lithium-6. (Courtesy: Northwestern University/Argonne National Laboratory)

A semiconductor material containing lithium-6 shows great promise for creating highly-efficient detectors of thermal neutrons. The 2D layered material was created and tested by scientists in the US and could someday be used in detectors at neutron scattering facilities – boosting the efficiency and spatial resolution of experiments. Devices based on the semiconductor material could also be developed as personal radiation monitors and have security applications such as detecting radioactive materials like plutonium.