High energy multi-mode nanosecond pulsed fiber amplifier based on the 940 nm LD pumping with effective suppression of the ASE and the SRS effect

We demonstrated, for the first time, an amplified spontaneous emission (ASE) and stimulated Raman scattering (SRS) free multi-mode nanosecond pulsed fiber amplifier based on the 940 nm LD pumping. The maximum pulse energy reached 15.3 mJ at the average output power of 306 W using a 100/400 Yb-doped extremely large mode area fiber. A near top-hat beam with M2 = 10.4 was achieved. This is the highest pulse energy generated from the 940 nm LD pumped multi-mode nanosecond pulsed fiber amplifier. In addition, comparative experiments based on the conventional 915 nm LD pumping and the 976 nm LD pumping were conducted. The results showed that the 915 nm LD pumping lead to intensive forward 1030 nm ASE, and the 976 nm LD pumping was limited by strong backward ASE power. These confirmed that the 940 nm LD pumping provided an effective method to suppress the ASE and the SRS effect in the high energy multi-mode nanosecond pulsed fiber amplifier.