High-power single-frequency 1014.8 nm Yb-doped fiber amplifier working at room temperature

A single-frequency 1014.8 nm Yb-doped fiber amplifier working at room temperature was investigated in detail with respect to gain fiber length, fiber geometry, and fiber host material, which can be frequency quadrupled to 253.7 nm for laser cooling of mercury. After optimization, an up to 8.06 W laser was achieved with a single-stage amplifier, and 19.3 W power was obtained with another boost amplifier, using polarization-maintaining Yb-doped single-mode fiber with a 10 μm core and 125 μm inner clad. The amplified spontaneous emission was 25 dB lower than the signal in the final output of the laser system. The laser has a linewidth of ~24 kHz without noticeable broadening after amplification. Further power scaling is limited by stimulated Brillouin scattering.