An ultrafast laser delivering 10.4 kW average output power based on a coherent combination of 12 step-index fiber amplifiers is presented. The system emits close-to-transform-limited 254 fs pulses at an 80 MHz repetition rate, and has a high beam quality (M2≤1.2) and a low relative intensity noise of 0.56% in the frequency range of 1 Hz to 1 MHz. Automated spatiotemporal alignment allows for hands-off operation.

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10.4 kW coherently combined ultrafast fiber laser

Coherent polarization beam combining (CPBC) of fiber lasers has the potential to scale the output total power while simultaneously maintaining good beam quality. In this paper, we will present the very recent technical advance in a single-channel coherently combinable linearly polarized narrow-linewidth fiber amplifier and high-power CPBC system. The noise property of a recently developed near 2 kW fiber amplifier and its feasibility in a CPBC system, CPBC of four 500-W-level fiber amplifiers and two kilowatt fiber amplifiers are demonstrated for the first time, which is also the first result for a 2 kW CPBC system. We have also performed numerical analysis on the performance scaling of CPBC, and deduced handy design guidelines for CPBC of a 64-element high-power system.

High-power coherent beam polarization combination of fiber lasers: progress and prospect [Invited]

Author(s): Albert, F; Couprie, ME; Debus, A; Downer, MC; Faure, J; Flacco, A; Gizzi, LA; Grismayer, T; Huebl, A; Joshi, C; Labat, M; Leemans, WP; Maier, AR; Mangles, SPD; Mason, P; Mathieu, F; Muggli, P; Nishiuchi, M; Osterhoff, J; Rajeev, PP; Schramm, U; Schreiber, J; Thomas, AGR; Vay, JL; Vranic, M; Zeil, K | Abstract: Plasma-based accelerators use the strong electromagnetic fields that can be supported by plasmas to accelerate charged particles to high energies. Accelerating field structures in plasma can be generated by powerful laser pulses or charged particle beams. This research field has recently transitioned from involving a few small-scale efforts to the development of national and international networks of scientists supported by substantial investment in large-scale research infrastructure. In this New Journal of Physics 2020 Plasma Accelerator Roadmap, perspectives from experts in this field provide a summary overview of the field and insights into the research needs and developments for an international audience of scientists, including graduate students and researchers entering the field.

2020 roadmap on plasma accelerators

This report presents the conceptual design of a new European research infrastructure EuPRAXIA. The concept has been established over the last four years in a unique collaboration of 41 laboratories within a Horizon 2020 design study funded by the European Union. EuPRAXIA is the first European project that develops a dedicated particle accelerator research infrastructure based on novel plasma acceleration concepts and laser technology. It focuses on the development of electron accelerators and underlying technologies, their user communities, and the exploitation of existing accelerator infrastructures in Europe. EuPRAXIA has involved, amongst others, the international laser community and industry to build links and bridges with accelerator science — through realising synergies, identifying disruptive ideas, innovating, and fostering knowledge exchange. The Eu-PRAXIA project aims at the construction of an innovative electron accelerator using laser- and electron-beam-driven plasma wakefield acceleration that offers a significant reduction in size and possible savings in cost over current state-of-the-art radiofrequency-based accelerators. The foreseen electron energy range of one to five gigaelectronvolts (GeV) and its performance goals will enable versatile applications in various domains, e.g. as a compact free-electron laser (FEL), compact sources for medical imaging and positron generation, table-top test beams for particle detectors, as well as deeply penetrating X-ray and gamma-ray sources for material testing. EuPRAXIA is designed to be the required stepping stone to possible future plasma-based facilities, such as linear colliders at the high-energy physics (HEP) energy frontier. Consistent with a high-confidence approach, the project includes measures to retire risk by establishing scaled technology demonstrators. This report includes preliminary models for project implementation, cost and schedule that would allow operation of the full Eu-PRAXIA facility within 8—10 years.

EuPRAXIA Conceptual Design Report

We report on the coherent beam combining of 61 femtosecond fiber chirped-pulse amplifiers in a tiled-aperture configuration along with an interferometric phase measurement technique. Relying on coherent beam recombination in the far field, this technique appears suitable for the combination of a large number of fiber amplifiers. The 61 output beams are stacked in a hexagonal arrangement and collimated through a high fill factor hexagonal micro-lens array. The residual phase error between two fibers is as low as λ/90 RMS, while a combining efficiency of ∼50% is achieved.

https://hal.archives-ouvertes.fr/hal-02995221/document

Coherent beam combining of 61 femtosecond fiber amplifiers.

Coherent beam combining in the femtosecond regime of a record number of 19 fibers is demonstrated. The interferometric phase measurement technique, particularly well suited to phase-lock a very large number of fibers, is successfully demonstrated in the femtosecond regime. A servo loop is implemented to control piezoelectric fiber stretchers for both phase and delay variation compensation. The residual phase errors are below λ/60  rms. Nearly 50% of the total energy is contained in the far-field central lobe. After compression, we obtain a combined pulse width of 300 fs identical to the master oscillator pulse width.

Highly scalable femtosecond coherent beam combining demonstrated with 19 fibers.

The XCAN collaboration program between the Ecole Polytechnique and Thales aims at developing a laser system based on the coherent combination of several tens of laser beams produced through a network of amplifying optical fibers [1]. As a first step this project aspires to demonstrate the scalability of a combining architecture in the femtosecond regime providing high peak power with high repetition rate and high efficiency. The initial system will include 61 individual phased beams aimed to provide 10 mJ, 350 fs pulses at 50 kHz.

XCAN – A coherent amplification network of femtosecond fiber chirped-pulse amplifiers

Coherent beam combining of a record number of 19 fibers is demonstrated with 300fs pulses. This result is achieved by controlling both phase and delay variations on each fiber channel in an interferometric measurement setup.

Coherent beam combining of 19 fibers in femtosecond regime

Coherent beam combining (CBC) [1] of fiber amplifiers provides an attractive mean of reaching simultaneously the high peak and high average powers required for various industrial, scientific and defense applications. By using this technique, the highest energy provided by an ultrafast fiber laser system was recently established [2]. For much higher energies, architecture has to be compatible with very large number of fibers [3]. Thus, the goal of the XCAN project is to overcome all the key scientific and technological barriers to the design and development of an experimental laser demonstrator with 61 fiber amplifiers coherently combined.

J. Le Dortz

Papers

Highly scalable femtosecond coherent beam combining demonstrated with 19 fibers.

XCAN – A coherent amplification network of femtosecond fiber chirped-pulse amplifiers

Coherent beam combining of 19 fibers in femtosecond regime

Highly scalable femtosecond coherent beam combining