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‘Be passionate, be bold and be willing to think outside the box,’ says Gérard Mourou, the French physicist awarded the 2018 Nobel Prize in Physics, along with Donna Strickland and Arthur Ashkin.
Together with Strickland, Mourou invented ‘chirped pulse amplification,’ a pioneering technique that paved the way for revolutionary ultrashort-pulse, very high-intensity lasers with extremely high energies beyond the physical limits of conventional technologies.
‘At the time, it seemed a very simple idea, and I was surprised no one else had thought of it first. With Donna, we took up the challenge, and by thinking outside the box and approaching the problem from a different angle, we achieved something remarkable,’ Mourou says. ‘It took three years for other researchers to replicate our work.’
In creating ultrashort high-intensity laser pulses without destroying the amplifying material, Mourou and Strickland first stretched the laser pulses in time to reduce their peak power, amplified and then compressed them. This breakthrough enabled a thousand-fold increase in peak power compared to previous pulsed laser techniques.
Today, after much refinement, the technology is used by millions of people every year undergoing corrective eye surgery with pinpoint laser accuracy. It is also playing a key role in the development of innovative radiography systems for medical imaging, and is leading to novel radiation therapies to treat cancer.
In the future, short-pulse, high-intensity lasers will push the frontiers of high-energy and particle physics, underpinning new particle accelerators that will use potent laser beams to deepen our knowledge of the physical world and unlock the mysteries of the universe.
Powerful influence
One key step on that path was the ICAN project. Gérard Mourou, a professor at École Polytechnique in France, led the EU-funded research infrastructure initiative which brought together scientists from across Europe to investigate how to harness the efficiency, controllability and high-power capability of fibre lasers. In addition to contributing to the development of next-generation particle accelerator technologies, the work is supporting ongoing research into important medical applications for isotope identification, nuclear pharmacology and proton therapy.
‘Chirped pulse amplification had given us high peak power, but for accelerator applications we also needed to improve average power and especially the efficiency. Chirped pulse amplification was only 0.1 % efficient: no one would build a particle accelerator with that degree of efficiency – the energy demands would be inconceivable,’ Mourou explains.
‘Therefore, the idea was to use fibres to carry the pulses. With the method developed in ICAN, we achieved efficiencies of 30 % to 40 %, and by using lasers, instead of needing kilometres like conventional particle colliders, we could accelerate particles in just centimetres.’
Because a single fibre can carry only a fraction of the energy that would be needed for future particle accelerators, the ICAN researchers also solved the problem of phasing the pulses across multiple fibres, synchronising 64 fibres in all.
‘A thousand or 10 000 fibres might be needed for high-energy physics applications, but the concept works – it is just a question of scaling it up and finding the resources to do so,’ Mourou says. ‘It’s important in science to take one incremental step at a time and projects such as ICAN are important building blocks in that process.’
Illumination
Mourou’s inspirational, albeit incremental, approach is reflected in another initiative: the Extreme Light Infrastructure (ELI). Mourou first proposed the idea for ELI in 2005 and launched an initiative by the European laser community to greatly expand research into advanced laser science.
‘We published our research paper on chirped pulse amplification in 1985. In the 35 years since, there has been enormous progress in laser science and its applications. The science hasn’t stood still and neither has my passion for it,’ Mourou says.