$7\times 7$ Multicore Fiber, Nanosecond Laser System Delivering 60 mJ Pulse Energy

Multicore fibers (MCF) offer a groundbreaking method that allows compact setups with an unprecedented number of channels [1]. In fact, MCFs offer an opportunity to integrate the parallel amplifiers in one fiber with a shared pump cladding and sharing amplification load across multiple cores. Therefore, MCFs are potential option in many applications, such as generation of extreme UV, incoherent beam combination, and pump source for other lasers. MCFs have scalable performance by the number of amplifying cores. While $4\times 4$ MCFs already provided high pulse energy [2] and high average power [3] with a diffraction limit beam quality, $7\times 7$ MCFs are the new generation of these systems and have the potential for J-class fiber laser amplifiers. In this work, a rod-type Ytterbium doped $7\times 7$ MCF is used both as an oscillator and amplifier in a Master Oscillator Power Amplifier (MOPA) system. The employed fibers are based on a step-index design with shared pump cladding and a rectangular core arrangement. This optical system containing 49 cores generates up to 10-mJ pulse energy as a seed for the amplifier (see Fig. 1).