Ultranarrow-linewidth, efficient amplification of low-power seed sources by a fiber amplifier

We report efficient amplification of an external cavity diode laser in the 1.06-microm range. The diode laser radiation is coupled into a Nd-doped silica fiber. The fiber is pumped by a diode array with up to 6.15 W of power. After a single pass of the seed radiation through the fiber amplifier, we observe up to 1.74 W of single-mode, narrow-linewidth laser radiation that is tunable over a relatively wide range of 1.060-1.067 microm. The output from our amplifier has the same spectral characteristics as the seed beam.