Double beam dream

Researchers at Rutherford Appleton Laboratory in Oxfordshire, UK, are developing what they claim to be the ’most intense laser in the world’. To help them in their goal they have been awarded a ?3m grant from the Council for the Central Laboratory of the Research Councils (CCLRC). Over a period of three years, scientists working at the Astra laser facility intend to upgrade the existing single-beam 10 terawatt system into a dual-beam facility which they claim will deliver a total power of 1 petawatt (10¹⁵ watts).

John Collier came up with the idea of a dual-beam laser when he took on the role of Astra group leader last March. Since then a team of researchers has been working on the project. ’To the best of my knowledge, what we have proposed is unique. Single beam petawatt level Titanium Sapphire systems are being developed around the world, but none that I know like this or with such an emphasis on scientific flexibility,’ says Collier.

Having two beams makes the laser facility far more flexible, he explains. ’There is a wealth of interesting experiments which could be performed in all sorts of geometries. For example, pump-probe experiments, whereby one beam could be used to "create" a situation, such as a shock wave in a lattice, and the other beam would be used to create a unique probe’. Both beams will be ’independently configurable and focusable’. The system should be capable of firing once every minute, compared with the current petawatt facility rate of one shot every 30 minutes.

The dual beam could enable scientists to investigate extreme conditions such as high temperatures and colossal magnetic fields in a controlled way in the laboratory.

When a laser beam is brought into focus to produce a plasma (a state of matter characterised by unbound negative and positive ions), it has a very high optical density, which approaches 10²² W cm^-2. Collier puts this into context: ’When light has an optical intensity of about 10¹⁶ W cm ^-2, the electric field of the light is comparable to the classical electric field between an electron and a proton in a hydrogen atom. Above 10¹⁹ W cm^-2, the acceleration and deceleration of an electron bathed in this field over an optical cycle become so extreme that it is governed by the Theory of Relativity. At 10²² W cm^-2 the plasma is so-called strongly relativistic and extreme conditions exist - huge magnetic and electric fields, enormous pressures, currents and temperatures’.

Under such conditions, ’you can drive nuclear fusion and nuclear fission reactions, and produce very high energy particles’, notes Collier.

Emma Davies