High Energy (100 mJ) and High Peak Power (8 MW) Nanosecond Pulses Delivered by Fiber Lasers and Self-Focusing Analysis Based on a Novel Mode Decomposition Method

Nanosecond (~10 ns) laser pulses with high peak power of 8 MW and high energy of 100 mJ are reported, which are generated by a cascaded pulsed Yb-doped fiber amplifier system working at a repetition frequency of 10 Hz. The peak power that is higher than the self-focusing threshold for Gaussian beams is achieved for the first time in the fiber lasers. To analyze the self-focusing threshold for multimode lasers in fibers, a novel mode decomposition based on the beam quality measurements is introduced. Based on the mode decomposition and nonlinear laser propagation simulations, the threshold of self-focusing for our case is estimated.