Blanc SIMI 9 - Blanc - SIMI 9 - Sciences de l'ingéniérie, matériaux, procédés, énergie

Wavefront-controlled femtosecond multicore fiber amplifier – MultiFemto

Submission summary

High energy ultrafast lasers, emitting laser pulses with temporal duration of hundred of femtoseconds, are acquiring increasing interest in the industrial and scientific areas owing to the impressive progress they have recently experienced, and unlocking numerous applications such as secondary radiation laser sources (e. g. EUV generation through high-harmonic generation), micromachining, scribing for the production of solar cells, cost-effective mask repairs for the semiconductor industry, and so on. Almost all these applications require a high energy per pulse, good spatial quality to allow proper focusing of the beam, in conjunction with a high repetition rate in order to become really effective. This can be rephrased as a need for ultrafast laser sources that can deliver high average and high peak power simultaneously in a diffraction-limited beam.

The peak power that can be achieved by a laser system depends on several characteristics of the source, namely gain bandwidth, level of spatial and temporal nonlinearities, material damage threshold, and saturation fluence of the gain medium. All these elements depend both on material aspects and system design, and are related with one another.

On the other hand, the average power than can be generated by a short pulse system is limited by quite different physical effects: availability of pump power, overall efficiency, thermal properties. These effects depend both on material properties (thermal conductivity) and on the amplifier geometry. In particular, the surface to volume ratio is of utmost importance to allow good heat exchange.

These sets of constraints for average/peak power performance are extremely demanding and have in the past been met only separately, by Ti:Sa lasers for the peak power, and by fiber lasers for the average power. Fiber lasers also have the great advantage of being very reliable, potentially compact and highly integrable. In order to break the barrier of the achievable peak power set by nonlinear effects and damage thresholds in fibers, a lot of research effort has recently been made mostly in two directions: first, the design of large mode area fibers that retain the transverse singlemode property, and second, the coherent combining of several fiber amplifiers.

This project is located at the intersection of these two solutions to overcome the power or energy limitation encountered in single mode or large mode area fibers: the main idea consists in the use of multicore fibers to amplify femtosecond pulses. Multicore fibers can be seen as large mode area fibers in the sense that the dimension of one core is limited by current day fiber manufacturing technology, but the number of cores can be arbitrarily large, thereby providing potentially a very large global mode area, hence pulse energy. However, the use of such fibers will require some phase control of each core in order to provide a diffraction limited output beam, therefore presenting similarities with coherent beam combining systems. As opposed to existing combining systems, however, the multicore solution is monolithic and integrated, which allows to retain one of the major advantage of fiber amplifiers.

The MultiFemto project will address all scientific and technical aspects of the use of multicore fibers for femtosecond pulse amplification. The aspects to be addressed are optimal multicore fiber design and fabrication, femtosecond pulse propagation in these complex guiding objects, wavefront control architectures adapted to the multicore geometry, and implementation of a demonstrator. Finally, since the femtosecond amplifier architecture will be based on the chirped-pulse amplification principle where pulses are stretched and compressed in time by controlling their spectral phase, this project constitutes a step forward in the full control of spatial / temporal phase of ultrafast beams.

Project coordination

Marc HANNA (INSTITUT D'OPTIQUE) – marc.hanna@institutoptique.fr

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

ONERA OFFICE NATIONAL D'ETUDES ET DE RECHERCHES AEROSPATIALES
PhLAM CENTRE NATIONAL DE LA RECHERCHE SCIENTIFIQUE (CNRS) - DELEGATION REGIONALE NORD-PAS-DE-CALAIS ET PICARDIE
LCFIO INSTITUT D'OPTIQUE
XLIM UNIVERSITE DE LIMOGES

Help of the ANR 549,594 euros
Beginning and duration of the scientific project: October 2011 - 36 Months

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