Single-photon transistor plans unveiled

Physicists in the US and Denmark have unveiled plans for an all-optical transistor-like device that can be turned on by a single photon.

A UK-led team of scientists has won European Union approval to prepare the ground for a laser-based nuclear fusion facility. The HiPER (high-energy laser fusion research) team will now start a three-year project to define the technologies that will be used to build an experimental prototype.

“Getting the laser technology right will be critical for the whole project,” Anne-Marie Clarke, HiPER’s project manager, told “We need to decide whether to use existing laser-based fusion techniques, such as those used in the Laser Mégajoule in France, or whether to develop new diode-pumped solid-state laser technology.”

Other large-scale laser facilities, such as Mégajoule and the National Ignition Facility now being constructed in Livermore, California, have been designed for military applications, but the primary purpose of HiPER will be to generate energy from nuclear fusion. The team is therefore focusing on the development of an all-optical “fast ignition” fusion process that it believes will be more suitable for commercial power generation plants.

This fast ignition is a two-step process. First, a laser that can deliver 0.2-0.3 MJ within a few nanoseconds is directed at a fuel pellet two millimeters across. This creates enough pressure to compress the pellet to a diameter of few microns and to generate temperatures of tens of millions of degrees. Ophir Optronics Ltd

Second, a short-pulse high-power laser (70-100 kJ in 10 ps) is used to ignite the gas. The fast-ignition technique is expected to require a smaller laser than conventional laser-fusion approaches – which typically demand several megajoules of laser energy to create the conditions needed for fusion – and should also ease the tolerances on the laser profile.

According to HiPER project co-ordinator Mike Dunne, the laser physics behind fast ignition is now being investigated by researchers around the world. The ultimate aim for the HiPER project is to develop the technology needed for a commercial power generation plant.

One of the goals of this three-year “preparatory” project will be to decide where to site the facility. The UK is currently the front runner, but Clarke says that HiPER would welcome bids from other member nations.

Another key objective will to pull together a consortium of nations and funding agencies that will contribute to the facility’s construction costs, currently estimated at $1 bn. The HiPER project is already formally supported by seven European nations, including the UK, the Czech Republic, France, Greece, Italy, Portugal and Spain, and endorsement by the European Commission will now allow the team to put all the elements in place to enable a decision on whether to build the facility. If approved, the HiPER team estimates that the prototype will take 4-5 years to build.

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