1.7-2.5 μm ns-pulsed amplified spontaneous emission in cryogenic silica Tm-doped fiber

We report a cryogenic, cavityless, gain-switched broadband ns-pulsed amplified spontaneous emission (ASE) source in a short single-mode silica thulium-doped fiber (TDF) cooled by liquid nitrogen (LN₂). Under the pump of a 1.55-μm ns-pulsed fiber laser with a maximum average power of 687 mW, broadband ASE spans 1750-2475 nm (20-dB bandwidth) with 140-mW average output power and 0.6 mW/nm spectral density at 2.3 μm. The broadband ASE originates from cooperative transitions at 1.9 μm and 2.3 μm and cavityless configuration. The filtered 2.3-μm output shows significantly enhanced slope efficiency of 30% at 77 K, due to the suppression of high-phonon-energy-assisted non-radiative quenching processes on ³H₄ level.