  We report on the design and whole characterization of low-noise and
affordable-cost Yb-doped double-clad fiber amplifiers operating at room
temperature in the near-infrared spectral region at pulse repetition rate of
160 MHz. Two different experimental configurations are discussed. In the first
one, a broadband seed radiation with a transform limited pulse duration of 71
fs, an optical spectrum of 20 nm wide at around 1040 nm, and 20 mW average
power is adopted. In the second configuration, the seed radiation is
constituted by stretched pulses with a time duration as long as 170 ps, with a
5-nm narrow pulse spectrum centered at 1029 nm and 2 mW average input power. In
both cases we obtained transform limited pulse trains with an amplified output
power exceeding 2 W. Furthermore, relative intensity noise measurements show
that no significant noise degradation occurs during the amplification process.
