High-power and highly efficient amplification of a radially polarized beam using an Yb-doped double-clad fiber.

We demonstrated the amplification of a radially polarized beam by using an Yb-doped double-clad fiber. The output power of the amplified beam reached 21 W at pump power of 30 W. The generation of amplified spontaneous emission was suppressed by applying a seed beam with sufficient power. Although the intensity distribution of the seed beam was well maintained after the amplification, partial transformation of radial polarization to azimuthal polarization was observed.