World's highest gain high-power laser amplifier developed

The world's highest gain high-power laser amplifier, which could amplify sounds from rustling of leaves to that of a jumbo jet, has been developed in the UK, an advance that may result in new radiotherapy modalities for the treatment of cancer.

The laser developed at the University of Strathclyde works on a relatively long, high-energy laser pulse that is made to collide in plasma with a short, very low energy pulse.

At the point where they collide they produce a beat wave, much like that of the two colliding water waves. The light pressure of the beat pattern drives plasma electrons into a regular pattern or echelon that mimics the beat wave.

"The Raman amplification in plasma is a fascinating concept that combines the ideas of Nobel Physics laureate C V Raman with plasma, optical and laser physics," said Professor Dino Jaroszynski of Strathclyde's Department of Physics who led the research.

These lasers will lead to new science and technology that could, for example, transform our understanding of high field physics and result in new radiotherapy modalities for the treatment of cancer.

Over the course of two pioneering experiments at the CLF, the scientists worked to adapt the 'Vulcan laser' so that two different colour lasers could exchange energy in a plasma.

The measured gain coefficient of 180 cm-1 is more than 100 times larger than achievable from existing high-power laser system amplifiers based on solid-state media.

The research was published in the journal Scientific Reports.

The colliding point acts as a very high reflectivity, time-varying mirror that sweeps up the energy of the high- energy pulse reflecting it into the low energy pulse, thus amplifying the low energy pulse and compressing its energy into an ultra-short duration pulse of light.

"Our results are very significant in that they demonstrate the flexibility of the plasma medium as a very high-gain amplifier medium. We also show that the efficiency of the amplifier can be quite large, at least 10 per cent, which is unprecedented and can be increased further," Jaroszynski said.

However, it also shows what still needs to be understood and controlled in order to achieve a single stage high-gain, high-efficiency amplifier module.

"One example of the challenges that we still face is how to deal with amplification of 'noise' produced by random plasma fluctuations, which is exacerbated by the extremely high gain. This leads to undesirable channels for the energy to go. We are making excellent progress and believe that we are in an excellent position to solve these problems in our next experimental campaigns," he said.

"Plasma is a very attractive medium to work with. It has no damage threshold since it is already a fully broken-down medium, therefore we can use it to amplify short laser pulses without the need for stretching and re-compressing," said Gregory Vieux who led the research team working at the CLF.

Laser amplifiers are devices that amplify light.Plasma, the ubiquitous medium of the universe, offers a way around this limitation because it is very robust and resistant to damage - plasma can be seen as a matter that has already been broken down into its smallest constituent elements: electrons and ions.

This is a very worthy goal because very intense laser pulses can be used for fundamental studies, such as accelerating particles, helping drive nuclear fusion or even extracting particles from vacuum and recreating the conditions inside stars or the primordial condition of the universe in the laboratory.

The highest power lasers in the world will be available for use at three research centres that are part of the European Extreme Light Infrastructure (ELI) project. It was funded by the Engineering and Physical Sciences Research Council.