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Optical physics

Flash Physics: Photons could interact in tiny silicon voids, plasma drives high-gain laser amplifier

31 May 2017 Hamish Johnston

Flash Physics is our daily pick of the latest need-to-know developments from the global physics community selected by Physics World‘s team of editors and reporters

Tiny voids: computer simulation of the electric field at a nanometre-sized cavity

Photons could interact in tiny silicon voids

Photons in relatively weak beams of light could be made to interact with each other by shining them through a piece of silicon with a specific set of voids cut through it. That is the conclusion of Hyongrak Choi, Mikkel Heuck, and Dirk Englund of the Massachusetts Institute of Technology in the US. They have done calculations that suggest a weak beam of light can create strong electric fields within a piece of silicon that contains a precise arrangement of nanometre-sized voids. The field can be as much as 10,000 times the strength of the electric field normally associated with such light. The presence of such a field would allow a photon to modify the index of refraction in the region that surrounds it. A second photon travelling through this region would be affected by this change – the result being an interaction between the photons. Normally, extremely intense laser light is required to create this effect. The ability to interact photons within much weaker light beams could lead to the development of new types of switches and other devices to create fast and energy-efficient optical communications networks that do not require electrical components. The effect is described in Physical Review Letters and could even be used to create devices for quantum computers in which information is encoded into photons.

Plasma drives high-gain laser amplifier

A plasma-based amplifier of laser light is described by its creators as having the highest ever gain. Built by an international team led by Dino Jaroszynski at the University of Strathclyde, the system takes picosecond-duration laser pulses carrying just a few picojoules of energy and boosts them up to about 100 mJ – which is a gain of about 100 million. The amplifier uses high-energy 100 J laser pulses at the Vulcan laser at the UK’s Central Laser Facility in Oxfordshire to create a plasma by firing the laser at a jet of hydrogen gas. The picojoule laser pulse to be amplified is fired at the plasma, where it collides with a high-energy laser pulse. The collision produces a beat wave of light that drives plasma electrons into a regular pattern that mimics the beat wave. This wave sweeps up the energy of the high-energy pulse and outputs it into the low energy pulse, resulting in a huge amplification of the low-energy pulse. An important feature of the amplification process is that the duration of the low-energy laser pulse is not increased significantly during the amplification process. “Our results are very significant in that they demonstrate the flexibility of the plasma medium as a very high gain amplifier medium,” says Jaroszynski. “We also show that the efficiency of the amplifier can be quite large, at least 10%, which is unprecedented and can be increased further.” However, he points out that random fluctuations in the plasma are also amplified, which contributes to noise in the amplified pulse. The team believes that plasma-based amplifiers could play important roles in the development of the next generation of high-power lasers. The research is described in Scientific Reports.


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