50 W low-noise single-frequency thulium-doped fiber amplifier at 1844 nm

In this work, we present a 50 W laser amplifier architecture operating at 1844 nm, encompassing a three-stage amplification architecture. The first two stages rely on core-pumping, while the final stage employs high-power cladding pumping. Core-pumping at 1560 nm enables a tunable output power of 2 W between 1830 nm and 1880 nm at the output of the second preamplifier. An integrated spectral filter comprising a circulator and a fiber Bragg grating (FBG) centered at 844 nm is used. Cladding pumping at 793 nm is implemented for power scaling, achieving over 50 W of output power with an optical signal-to-noise ratio (OSNR) exceeding 60 dB. The amplifier exhibits low intensity noise, with an RMS noise of 0.006% in the 1 kHz-10 MHz range, without any sign of Stimulated Brillouin Scattering (SBS). These results highlight the amplifier's suitability for demanding industrial and scientific applications, including quantum computing, where narrowband emission, low Relative Intensity Noise (RIN), and reliability are critical.