We report on the experimental demonstration of a fiber laser array composed by 7-elements coherently combined to obtain a total power up to 10kW. The architecture is based on a narrow line single mode master oscillator whose emission is modulated to widen the linewidth up to 47 GHz. The large-linewidth seed is then split in multiple replicas that can be amplified up to 2kW each. Then, a hexagonal array of collimated laser beams is realized by means of a custom opto-mechanical tiled aperture structure. Finally, the beams are overlapped by means of an optical system and coherently combined controlling the single source phases through Lithium-Niobate phase modulators, whose correction signals are computed by a proprietary hill-climbing algorithm.
With the developed system it was possible to carry out a characterization campaign to evaluate the vulnerability of different targets, materials and surface finishes, together with the definition of the relevant damage assessment criteria. Some of the most notable results will be presented. The laser Facility, built for this purpose, where the demonstrator has been integrated and tested will be presented too.
Coherent beam combining techniques aim to obtain high-power laser beams with good quality and thus enabling several specific applications such as long-range communications, remote power delivering or L-DEW applications. They have received a renewed interest given the very good performances obtainable with high power fiber lasers adopting MOPA architectures and phase locking feedback loops. In the case of fiber lasers, the specific power of a single amplifier is limited by the deleterious effect of SBS. One can enhance the threshold of SBS widening the bandwidth of the field in the amplifier but this contrasts with the need of a spectrally pure field for the adoption of CBC architectures based on phase detection. Arrays with a large number of elements have been demonstrated for narrow-band systems, while wideband phase locking has been reported only in the case of a limited number of elements. The adoption of multi-KW fiber laser amplifiers requires bandwidths of the order 30 GHz. In this paper, we report on the experimental demonstration of a 7-element array coherently combined up to a spectral bandwidth of 47 GHz. The architecture is based on a narrow line single mode master oscillator whose emission is phase modulated to widen the bandwidth. Amplified fields are summed in a tiled aperture geometry and far field PIB is adopted as a metrics for a perturbation hill-climbing algorithm. Phase-locking results and convergence dynamics are analyzed in relation to the bandwidth properties of the oscillator modulation.
Plasma wakefield acceleration is the most promising acceleration technique known nowadays, able to provide very high accelerating fields (> 100 GV/m), enabling acceleration of electrons to GeV energy in few centimeters. Here we present all the plasma related activities currently underway at SPARC LAB exploiting the high power laser FLAME. In particular, we will give an overview of the single shot diagnostics employed: Electro Optic Sampling (EOS) for temporal measurement and optical transition radiation (OTR) for an innovative one shot emittance measurements. In detail, the EOS technique has been employed to measure for the first time the longitudinal profile of electric field of fast electrons escaping from a solid target, driving the ions and protons acceleration, and to study the impact of using different target shapes. Moreover, a novel scheme for one shot emittance measurements based on OTR, developed and tested at SPARC LAB LINAC, will be shown.
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