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A Revolutionary Architecture to solve Grand Scientific and Societal Challenges: the Coherent Amplifying Network Laser


The future may be fiber accelerator

The challenge of producing the next generation of particle accelerators, for both fundamental research at laboratories such as CERN and more applied tasks such as proton therapy and nuclear transmutation, has been taken up by the high-intensity laser community. A consortium of physicists led by Gérard Mourou of École polytechnique proposes a revolutionary laser infrastructure inspired by the telecommunication technology. This new laser architecture composed of massive arrays of thousands of fiber lasers could be the driving force behind next generation particle accelerators. After having worked on a feasibility study, the International Coherent Amplification Network (ICAN) consortium firmly believes so. The results of this study are published today in Nature Photonics.

Ultrahigh power lasers: an efficient way to accelerate particles

Laser can provide in a very short time measured in femtoseconds, bursts of energy of formidable power counted in petawatts or thousand times the power of all the power plants in the world. One important application demonstrated today has been the possibility to accelerate particles to high energy over very short distances measured in centimeters rather than kilometers as it is the case with today conventional technology. This feature is of paramount importance when we know that today high energy physics is limited by the prohibitive size of accelerators, tens of kilometers and cost billions of euros. Reducing the size and cost by a large amount is of critical importance for the future of high energy physics.

Compact accelerators are also of great societal importance for applied tasks in medicine such as a unique way to democratize proton therapy for cancers treatment, or the environment where it offers the prospect to reduce lifetime of dangerous nuclear waste by in some cases from 100 thousand years to tens of years or even less.

How can we make the high-intensity laser work at high repetition rate and efficient?

As of today, there are two major hurdles that prevent the high-intensity laser from becoming a viable and widely generalized technology in the future. First, the high-intensity laser can today only operate at a rate of one laser pulse per second, when for practical applications it needs to operate at 104 times per second. The second is, ultra intense lasers are notorious for being very inefficient, as they require much more energy than they deliver (typically the efficiency is of 10-3 to 10-4). Most applications demand average power in the range of 10kW to tens of Megawatt, which means that it is economically not feasible to produce this power with such a poor efficiency. So, in spite of impressive acceleration performance, these two reasons still preclude laser acceleration to be considered for fundamental or societal applications.

Bridging the technology divide

To bridge the formidable technology divide, the ICAN consortium initiated and coordinated by the Ecole polytechnique, composed by ORC, Jena, and CERN, as well as 12 other prestigious laboratories around the world, proposed to the European Union to explore a revolutionary laser architecture that could fulfill all the desired conditions. The basic idea of this consortium is to replace the conventional monolithic single rod amplifier that typically equips lasers by a network of fiber amplifiers and telecommunication components, a radically novel architecture called CAN for Coherent Amplifying Network.

A typical CAN laser for high-energy physics will utilize 100 thousand fibers, each carrying a small amount of laser energy. It offers the advantage of relying on well tested telecommunication elements such as fiber lasers and other components. The fiber laser offers an excellent efficiency (>30%) due to laser diode pumping. It also provides a much larger surface cooling area and therefore makes possible high repetition rate operation. The most stringent difficulty is to phase the lasers within a fraction of a wavelength. This difficulty seemed insurmountable but a major roadblock has in fact been solved: preliminary proof of concept suggest that 100 thousand fibers can be controlled to provide a laser output powerful enough to accelerate electrons to energies of several GeV at 10 kHz repetition rate - an improvement of at least 100 thousand times over today’s state of the art

Beyond electron Acceleration: laser Driven transmutation and medical Applications

Such a combined fiber–laser system should provide the necessary power and efficiency that could make economical the production of a large flux of relativistic protons over millimeter lengths as opposed to few hundred meters. One important societal application of such a source is to transmute the waste products of nuclear reactors, which at present have half-lives of hundreds of thousands of years, into materials with much shorter lives, on the scale of tens of years, thus transforming dramatically the problem of nuclear waste management. CAN technology could also find important applications in areas of medicine such as proton therapy, where reliability and robustness of fiber technology could be decisive features.

ICAN requires expertise in many walks of science and technology, which has been sourced from around the world. The four main project partners are:
- Ecole polytechnique in Paris, France, led by the ICAN project leader Gerard Mourou ;
- the optical fibre laser groups at the Fraunhofer Institute for Applied Optics and Precision Engineering and the Institute of Applied Physics of Friedrich-Schiller University in Jena, Germany, (Andreas Tünnermann) ;
- ORC, University of Southampton in the UK (David Payne) ;

Experts from other related and famous organizations such as KEK (Japan), MPQ Garching, ONERA, Institut d’Optique (France), University of Michigan, and University of Oxford (UK) bring their own areas of expertise to the project.

A series of workshops and conferences will be held until July 2013, at which stage the first hardware designs will be summarized for a single-stage demonstrator laser system aiming for >10 J per pulse, >10 kHz performance with pulses of 100–200 fs. The main results of the work done by the ICAN consortium will be announced and discussed at a conference taking place at the CERN on June 27-28, with the participation of prominent academic institutions as well as industrial companies, among which is Thales.

Gerard Mourou, Bill Brocklesby, Toshiki Tajima and Jens Limpert, The future is fibre accelerators, Nature Photonics, VOL 7 | APRIL 2013

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About the École Polytechnique
Widely internationalized (30% of the student body, 23% of faculty members), École Polytechnique combines research, education and innovation at the highest scientific and technological level. Its three degree programs – ingénieur polytechnicien, Master’s and PhD – are highly selective and promote a culture of excellence with a strong emphasis on science, combined with humanist traditions.
École Polytechnique educates responsible men and women who are prepared to lead complex and innovative activities which respond to the challenges of 21st century society. With its 20 laboratories, all joint research facilities with the National Center for Scientific Research (CNRS), the École Polytechnique Research Center works to expand the frontiers of knowledge in the major interdisciplinary issues facing science, technology and society.
As a ParisTech member institute, École Polytechnique is also one of the driving forces behind the Paris Saclay Campus project, along with its 22 academic and scientific partners.