We report on a high-energy, all-fiber nanosecond laser system seeded by a laser diode driven by 1.3 kHz electrical pulses and pumped by a 10 Hz synchronized pulsed pumping scheme. In the main amplifier, two stages of M-type 100-μm-core-diameter Yb-doped fibers (YDFs) were employed for mode homogenization, followed by the final amplification stage utilizing a 200-μm high-absorption YDF. A maximum pulse energy of 81 mJ and a peak power of 12.1 MW were achieved, corresponding to a slope efficiency of 34.2%. Notably, no significant stimulated Raman scattering component was observed in the output spectrum. The entire system featured an all-fiber-based architecture equipped with a low-repetition-rate pulse-picking amplification system. To the best of our knowledge, these results represent the highest peak power and pulse energy reported currently for a low-repetition-rate nanosecond all-fiber-based master oscillator power amplifier laser operating at 1064 nm.

High-energy nanosecond pulses at wavelengths beyond 2.5 μm in the mid-infrared (mid-IR) region are of significant interest for applications such as polymer processing, minimally invasive surgery, laser ranging and infrared countermeasures. While rare-earth-doped fluoride fibers provide a compact and robust platform for mid-IR pulse generation, achieving millijoule (mJ)-level nanosecond pulses beyond 3 μm remains challenging. In this work, we demonstrate high-energy nanosecond pulse generation at 3.17 μm using a master oscillator power amplifier based on a 980 nm diode-pumped Er3+/Dy3+ co-doped fluoride fiber. Seeded by an actively Q-switched oscillator operating at a 1 kHz repetition rate, the system delivers 0.68 mJ of pulse energy with a pulse width of 132 ns and a peak power of 4.8 kW, while maintaining single-transverse-mode operation (M2 = 1.2–1.3). To the best of our knowledge, this work represents the first report on mJ-level nanosecond pulse generation beyond 3 μm from a fiber-based system.

Based on a 4f system, a 0° reflector and a single laser diode side-pump amplifier, a new amplifier is designed to compensate the spherical aberration of the amplified laser generated by a single laser diode side-pump amplifier and enhance the power of the amplified laser. Furthermore, the role of the 4f system in the passive spherical aberration compensation and its effect on the amplified laser are discussed in detail. The results indicate that the amplification efficiency is enhanced by incorporating a 4f system in a double-pass amplifier and placing a 0° reflector only at the focal point of the single-pass amplified laser. This method also effectively uses the heat from the gain medium (neodymium-doped yttrium aluminium garnet) of the amplifier to compensate the spherical aberration of the amplified laser.

High-power femtosecond mid-infrared (MIR) lasers are of vast importance to both fundamental research and applications. We report a high-power femtosecond master oscillator power amplifier laser system consisting of a single-mode Er:ZBLAN fiber mode-locked oscillator and pre-amplifier followed by a large-mode-area Er:ZBLAN fiber main amplifier. The main amplifier is actively cooled and bidirectionally pumped at 976 nm, generating a slope efficiency of 26.9%. Pulses of 8.12 W, 148 fs at 2.8 μm with a repetition rate of 69.65 MHz are achieved. To the best of our knowledge, this is the highest average power ever achieved from a femtosecond MIR laser source. Such a compact ultrafast laser system is promising for a wide range of applications, such as medical surgery and material processing.