High Energy Pulsed Operation of a Yb Fibre MOPA with Amplified Spontaneous Emission Output

High energy pulsed fibre lasers are attractive to numerous applications in areas including industry, science, metrology and defense due to their excellent characteristics such as high average powers, a diffraction-limited beam quality, compactness and high flexibility in operation. However, their pulse energy is often limited by nonlinear optical phenomena, such as SBS (Stimulated Brillouin Scattering), SRS (Stimulated Raman scattering), self-focusing, etc., due to the small core size, resulting in unstable operation and catastrophic damage of the fibre. Enlarging the core size along with shortening the fibre length is a simple and straightforward way to overcome this problem, but at the expense of beam quality degradation and increased thermal effects. Fibre-based superfluorescent sources (FSS), sometimes referred to as amplified-spontaneous-emission (ASE) fibre light sources, can be an alternative way to achieve higher pulse energy from a typical step-index fibre while preserving the good beam characteristics of the fibre laser. Since the FSS has a broad spectrum without longitudinal modes, its spectral power is smaller than that of the fibre laser, increasing SBS threshold and, hence, generation of a high energy pulse. In this study, we report pulsed operation of the fibre-based superfluorescent light source. From a Yb fibre MOPA using an ASE source as a seed, we successfully generated high energy superfluorescent light pulses and investigated its performance for different repetition rates, pulse widths, and spectral linewidths. Furthermore, the results were compared with those of a Yb fibre laser.