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

Experimental results are reported for the noise characteristics of an Yb-doped fibre amplifier pumped at 975 nm, used as a booster of a low-noise narrow-linewidth single-frequency 1083-nm wavelength laser diode. The maximum output power of the amplifier is 1.2W with a gain larger than 30 dB. An increase of the intensity-noise spectral density relative to the signal, by approximately 6.5 dB, is in introduced by the amplification process, due to signal-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. The spectral broadening due to am amplifier phase noise was measured to be less than 300 Hz with a 5-kHz-linewidth Nd:YAG laser and that for the 300-kHz-linewidth diode laser at 1083 nm is therefore expected to be in the same range.