Noise characteristics of a high-power ytterbium-doped fibre amplifier at 1083 nm

Experimental results are reported for the noise characteristics of an Yb-do ped fibre amplifier pumped at 975 nm, used as a booster of a low-noise narr ow-linewidth single-frequency 1083-nm wavelength laser diode. The maximum o utput power of the amplifier is 1.2W with a gain larger than 30 dB. An incr ease of the intensity-noise spectral density relative to the signal, by app roximately 6.5 dB, is in introduced by the amplification process, due to si gnal-amplified spontaneous-emission (ASE) beat noise. A remarkable increase of the noise level with decreasing frequency is observed below approximate to 35 kHz, probably due to technical noise of the amplifier pump diodes. T he spectral broadening due to am amplifier phase noise was measured to be l ess than 300 Hz with a 5-kHz-linewidth Nd:YAG laser and that for the 300-kH z-linewidth diode laser at 1083 nm is therefore expected to be in the same range.