BLANC - Blanc

Coherent Amplification Network – CAN

Submission summary

We are proposing to study a new amplifying laser concept based on Coherent Amplification Network (CAN). The final objective is to produce pulses with intensity in the relativistic regime at very high repetition rates key to real world applications for relativistic optics. This implies to produce simultaneously high peak and high average power. Let's recall that today, TW peak power can be produced with only 10 W average power, i.e. low repetition rates (few kHz). For many real world applications of relativistic optics like particle acceleration and generation of x-ray and gamma- ray sources, much higher average power from kW to MW are required. The philosophy behind the approach is to build a laser system with the maximum surface area, required to dissipate the heat deposited in the amplifying medium. The ideal system will be built out of single mode amplifying fibers. Because of their very favorable volume to surface area ratio, extremely high average power can be generated by one fiber in excess of the kW. However, in order to be in the relativistic regime, i.e. greater than 10^18W/cm2, average power is not sufficient. We need to produce joule to kilojoule energy per ultrashort pulse, which implies to combine many fibers coherently. As a rule of thumb we assume around 1mJ per pulse and per fiber. As we will see later, we are contemplating at systems with 10^3-10^6 amplifying fibers to form a Coherent Amplifying Network (CAN). The construction of such a system will rely on massive manufacturing of small telecommunication parts. Telecommunication parts such as diode-pumped fibers are very efficient, reliable, low cost, and rugged. The CAN's philosophy departs from the conventional 'open' cavity's one with less but non identical parts. Besides the possibility to simultaneously provide high peak and high average power with high efficiency, the technique gives independent control of the output beam spatial and temporal coherence. In addition to be rugged CAN offers the additional benefit to be inexpensive and low maintenance. It could be extended to very large N=10^6 to solve very challenging problems like the next CERN Linear Collider (CLIC). We want to study in this proposal the possibility to coherently add a large number N of single mode fibers, with N>50. If this goal is achieved we understand that by phasing n fiber bundles we could phase an arbitrarily large number of fibers, up to N^n. Several techniques have been proposed for coherent combining. This includes beam combining by nonlinear effects, self-organized cavity and beam combining by active phase control. This later technique offers the advantage of being scalable because the energy and/or the power seen by one fiber can be maintained below the damage threshold of the fiber. The very large intensity can be then obtained by additioning a very large number of fiber amplifiers. Up to know, beam combining by active phase control of fiber amplifiers has been demonstrated with a relatively small number of fibers. The aim of the CAN project is now to study and demonstrate beam combining of a large number of fibers which has not been addressed in previous studies. The goal is to make a proof-of-concept at a limited cost. Consequently passive fibers will be used. On the other hand, in order to address all the aspects of coherent beam combining with amplifying fibers, the phase fluctuations in a single high-power fiber amplifiers will be theoretically and experimentally studied to determine the typical characteristic times and amplitudes of these fluctuations for different operating regimes including the femtosecond regimes. The expected results of the CAN project is to have a clear picture of all the key parameters for producing intensity in the relativistic regime based on the coherent combining of a large number of fiber amplifiers. In this project the fundamental physics of the phase fluctuations in a single high-power fiber amplifiers will be addressed. This study will impact on the whole system characteristics an the required performances of the phase analysis and control feedback loop. All the specific technologies entering in the combining system compatible with a large number of fibers will be analyzed and compared in order to identify the best methods. These includes new methods for collective measurement of the phase of the beam from each fiber, a new high speed phase modulator technology based on electrooptic ceramics for controlling the phase of each fibers and optimized electronic feedback loop. In this project, a complete laboratory demonstrator with N=64 passive fibers will be realized. To our knowledge, this will be the beam combining system with the largest number of fibers ever made. The CAN project is of first importance to obtain a clear roadmap for future development of compact and efficient fiber-based laser to achieve in the future intensity in the relativistic regime.

Project coordination

Gérard MOUROU (Autre établissement d’enseignement supérieur)

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.

Partner

OFFICE NATIONAL D'ETUDES ET DE RECHERCHES AEROSPATIALES (O.N.E.R.A.)

Help of the ANR 350,000 euros
Beginning and duration of the scientific project: - 24 Months

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